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Transcript
COLLEGE OF NATURAL
RESOURCES
Student Handout
MODULE: Fundamentals of Plant Protection
UNIT: Entomology
Year 1 Semester
Compiled by: Karma Penjore & Dr. Jamba Gyeltshen
August 2009
CONTENT
Introduction to entomology ............................................ 3
A Class of Distinction ................................................................................................ 3
The Dominance of Insects ......................................................................................... 4
Why are insects so successful? .................................................................................. 5
Economic importance - how do insects affect us? ..................................................... 6
Features of Arthropods .............................................................................................. 7
Classification of Insects .................................................. 9
Insect orders ............................................................................................................... 9
Insect orders of agricultural importance .................................................................. 11
Insect morphology ........................................................ 13
Head ......................................................................................................................... 13
Antennae .............................................................................................................. 13
Eyes ...................................................................................................................... 15
Mouthparts ........................................................................................................... 16
The insect thorax ...................................................................................................... 19
Legs ...................................................................................................................... 20
Wings ................................................................................................................... 20
Abdomen and external genitalia .............................................................................. 24
Reproduction in insects ................................................ 26
How do insects find their mates? ............................................................................. 26
Types of reproduction in insects .............................................................................. 26
Insect growth and development .................................... 26
Insect life cycle ........................................................................................................ 27
Metamorphosis ......................................................................................................... 28
Insect seasonal cycles .............................................................................................. 30
Larval forms ............................................................................................................. 31
Pupal forms .............................................................................................................. 32
Insect Collection ........................................................... 34
Purpose of collecting and preserving insects ........................................................... 34
Insect collection equipment and materials ............................................................... 35
Preserving insects..................................................................................................... 38
Hard-Bodied Insects............................................................................................. 38
Soft-Bodied Insects .............................................................................................. 39
Pinning, mounting and displaying insects .................... 40
Equipment required .................................................................................................. 40
Pinning Insects ......................................................................................................... 40
Labeling Insects ....................................................................................................... 42
REFERENCE: .............................................................. 43
2
Introduction to entomology
Entomology is a branch of zoology that deals with the study of insects. The term is
derived from the Greek word Entomon = Insects and logos = study. Agricultural
Entomology deals with the study of insects that affect agriculture. There are other
branches of entomology, such as medical entomology, veterinary entomology, and
forensic entomology (study of insects inhabiting decomposing remains). With over
one million different species inhabiting the earth, insects make up more than 80% of
all described animal species and form a major component of the earth's biodiversity.
They have different roles: as plant consumers and herbivores, food source for other
organisms, scavengers and detritivores (feeding on decomposing organic matter),
predators and parasites. Insects also directly affect human welfare by competing with
us for food and transmitting diseases. However, not all insects are detrimental to us.
For example, bees are used to produce honey, silkworms to produce silk and similarly
numerous predatory species are used to control pests in our crops.
A Class of Distinction
Adapted from John R.Meyer,
(http://www.cals.ncsu.edu/course/ent425/library/tutorials/index.html)
We humans are such a self-centered species that we seldom stop to acknowledge or
appreciate the importance of other living organisms in our environment. Our prowess
in science and technology has given us unparalleled control over our physical
environment, and as a result, we have developed an inflated view of our own
importance in the web of life. Although we have learned to use tools, dam rivers,
level mountains, and harness atomic power, we are still dependent on Mother Nature
for the countless housekeeping chores that keep our environment stable and
healthy. Indeed, we are relatively minor players in the ecological drama that
continually unfolds all around us. If humans were to suddenly vanish from the planet,
there would be no ecological calamity, no massive extinctions, and no tears shed for
our demise. Remnants of human civilization would soon be smothered in vegetation,
the forests would reclaim our cities, and life would go on without us just as it did for
millions of years before our ancestors first reckoned the passage of time. Sadly, the
earth would probably be better off without us.
In simplest terms, life (as we know it) exists on planet earth because of a global cycle
of production and consumption that hinges almost exclusively on green plants as
primary producers and insects as primary consumers. These two life-forms
overshadow all other multi-cellular organisms in terms of abundance and
diversity. They are mutually dependant on one another for survival, and form a
nucleus around which all terrestrial and fresh-water ecosystems are built. Without
green plants and the organic molecules they produce through photosynthesis, all
animal life would collapse from starvation. Without insects and other decomposers,
green plants would quickly exhaust their nutrient supplies, dead organic matter would
Entomology handout
Page 3
accumulate in putrid, rotting heaps, and many species of flowering plants would
become extinct for lack of insect pollinators.
In a sense, we owe our very existence to members of the insect world -- creatures we
often fear or despise. We expend considerable resources trying to eliminate these
animals from every facet of our daily lives, but in fact, we could never hope to survive
without them -- they make the earth habitable for us. Like tiny maids and butlers,
they perform Nature's housekeeping tasks with competence and efficiency. Nothing
else -- animal, vegetable, or mineral -- could ever take their place. By virtue of their
diversity, their world-wide distribution, their ecological importance, and their impact
on other life-forms, the insects are indeed a class of distinction.
The Dominance of Insects


Figure 1
Number of Species
Entomologists estimate that over 800,000 insect species have been named and
described since Carolus Linnaeus (1707-1778) founded the modern system of
nomenclature (genus and species) for all plants and animals. The entire plant
kingdom, by comparison, contains between 400,000 and 500,000 species. Thus,
insects represent more than half (about 53%) of the 1.5 million species of living
organisms known to science (Figure 1).
Number of individuals
Another way to look at the dominance of insects is to consider the distribution and
density of individual species or populations. Because of their small size and high
reproductive potential, insect populations often grow to epic proportions. A single
colony of Australian termites can swell to several million individuals within an
4
earthen mound 20-25 feet tall. A swarm of migratory locusts may contain up to 10
billion individuals, cover an area of several thousand hectares, and have a total
biomass of over 30,000 metric tons. Above the arctic circle, hordes of mosquitoes
and black flies can make life miserable for any warm-blooded animal. In some cases,
these biting flies are so abundant and persistent that large animals, such as reindeer,
have been known to die from the massive loss of blood (desanguination). In the
tropics, ants are the most pervasive and diverse of all animal species. Colonies of
driver ants (Dorylus sp.) on the African savannah may contain 20 million individuals.
Distribution
A third way to assess the dominance of insects is to examine their abundance and
diversity in a wide range of ecological habitats. Indeed, insects are found in virtually
every terrestrial and fresh-water environment on the face of the earth. They live
everywhere from mountain tops in the Himalayas to tide pools at the
seashore. Dozens of eyeless species spend their entire lives in the total darkness of
underground caverns. At least 40 species live on the polar ice caps of Antarctica,
others exist on the surface of glaciers, or near the edge of melting snow fields. A few
species can survive in hot springs where the water temperature is 50oC; others inhabit
deserts where water is scarce and daytime temperatures exceed 60oC. Insects live
both above and below the surface of rivers, streams, lakes, and ponds. One species of
water strider makes its home among floating seaweed in the Sargasso Sea, nearly
2400 kilometers (1500 miles) from the nearest land mass. The petroleum fly
(Helaeomyia petrolei), develops in pools of crude oil in the California oil fields. A
related species, the brine fly (Ephydra cinera), thrives in the high salinity of Utah's
Great Salt Lake. In fact, the only place on earth where insects are not plentiful is in
the ocean depths. Most marine environments are filled by another successful group of
arthropods, the Crustacea.
Why are insects so successful?
There are many attributes of insects that have allowed for their success and
diversification.




Exoskeleton -this is a marvelous structure that not only gives shape and
support to the body's soft tissues, but also provides protection from attack or
injury, minimizes the loss of body fluids in both arid and freshwater
environments, and assures mechanical advantage to muscles for strength and
agility in movement.
Small size -there are many more niches for small organisms than for large
organisms. For instance, one insect could live solely on and in the seeds of a
specific plant.
Short life cycle - this allows many generations within a given time for
selection and evolution to take place.
Reproductive potential - large numbers of offspring are produced to
compensate the mortality due to adverse conditions. When large numbers of
offspring are produced, there are also large variation in the population for
natural selection and evolution to act upon. A honey bee queen lays as many
Entomology handout
Page 5





as 4,000 eggs a day, and an African termite queen can lay as many as 43,000
eggs a day.
Metamorphosis- Variation of life style of different stages in an insect's life
(e.g. caterpillar versus butterfly) reduces competition for resources within the
species.
Wings-the ability to fly are relatively rare outside insects and have allowed
them to colonize freely.
Adaptability - A combination of large and diverse populations, high
reproductive potential, and relatively short life cycles, has equipped most
insects with the genetic resources to adapt quickly in the face of a changing
environment.
Sensory sophistication - the sensory capabilities of insects surpasses most
other organisms.
Adaptation of appendages - mouthparts, wings and legs have often become
highly specialized.
Economic importance - how do insects affect us?
Insects affect us in different ways. Some are beneficial while some are harmful. The
beneficial and detrimental effects of insects are as discussed below.
Beneficial effects
1. Pollination- Insects such as honey bees, beetles and wasps aid in pollinating
our crops and fruit trees. Crops in Rosaceae, Cucurbitaceae and Leguminosae
are exclusively pollinated by bee. It is estimated that 80% of the commercial
food crops are pollinated by honey bees.
2. 2: Bio-control agents- Some parasitic and predatory insects are excellent biocontrol agents for controlling other injurious insects. Example Encarsia
formosa is an excellent bio-control agent for white flies on tomatoes and
potatoes.
3. Production of products - Honey, wax, silk (from Bombyx mori), shellac (from
Laccifer lacca) and cochineal (red dye widely used in cosmetics, medicinals
and food products) derived from, a scale insect, Dactylopius coccus.
4. Nutrient recycling - Insects feed on dead and decaying plants, animals and
animal excreta and help in recycling the nutrients. Some insects burrow into
soils and improve the soil structure and texture. Examples are dung feeders
and termites.
5. Source of food - over 500 species of insects are used as food by humans usually crickets, grasshoppers, beetle, wasp, butterfly larvae, bugs etc
6. Miscellaneous – Some insects are used for medicinal purpose, decoration,
hobby, and pets.
Detrimental effects
Destruction or spoilage of food (both fresh and stored) and crops (including
forests)
2. Damage to goods - leather, paper, textiles, (by beetles, cockroaches, silverfish
or moths), timber (by termites and different types of borers)
1.
6
3.
4.
5.
6.
7.
Transmits disease in plants and animals.
Possess venoms and cause allergies
Some insects are a nuisance to our well being -house flies, ants, mosquitoes
Cause phobias – fear of grisly caterpillars or spiders (arachnophobia)
Require use of pesticides and other poisons, which often harm other animals
Features of Arthropods
Arthropoda (from arthros = jointed, podos = foot) is the largest phylum in the Animal
Kingdom. Arthropods are segmented animals which have jointed appendages. All
arthropods have:
All arthropods possess :






Exoskeleton - a hard protective covering around the outside of the body
(divided by sutures into plates called sclerites)
Segmented body
Jointed limbs and jointed mouthparts - that allow extensive specialization
Bilateral symmetry - whereby a central line can divide the body into two
identical halves, left and right
Ventral nerve cord - as opposed to a vertebrate nerve cord which is dorsal
Dorsal blood pump
The Phylum Arthropoda includes the class Insecta and other classes like the
Arachnida, the Chilopoda, the Diplopoda and the Crustacea. It is with these groups
that the insects, especially the wingless ones, are most likely to be confused and the
main characters that are used to differentiate these classes are:
Entomology handout
Page 7
Class Arachnida (arachnids): spiders, scorpions, ticks, mites,
etc.
Arachnids possess:




2 body segments - cephalothorax and abdomen
8 legs
1 pair of chelicerae
no antennae
University of Sydney
Class Chilopoda (centipedes)
Chilipods are quick moving predators with poison glands which
possess:




body flattened and multi-segmented
1 pair of legs per body segment
1 pair of antennae
1st pair of legs modified into venomous “fangs”
University of Sydney
Class Diplopoda (millipedes)
Diplopods are slow moving vegetarians which possess:



Many body segments
2 pair of legs per body segment
1 pair of antennae
University of Sydney
Class Crustacea (crustaceans): crabs, shrimp, barnacles,
sowbugs, etc.
Crustaceans possess:



Two body regions – Cephalothorax and abdomen
2 pairs of antennae
Varied number of legs (usually five)
University of Sydney
Class Insecta (Insects); beetles, bugs, wasps, moths, flies, etc.
Insects possess:




3 body segments
6 legs
1 pair of antennae
Most flying insects possess two pairs of wings
8
University of Sydney
Classification of Insects
All living organisms are placed into certain groups or categories for classification and
identification. The seven most commonly used categories are:
Kingdom- Animal
Phylum - Arthropoda
Class – Insecta
Order – Lepidoptera (Butterflies and moths)
Family - Noctuidae
Genus - Helicoverpa
Species – armigera
The species is the basic taxonomic category and may be defined as groups of actually
interbreeding natural populations which are reproductively isolated from other such
groups. Closely related species are grouped together in the next higher category - the
genus. Related genera make up a family and related families are grouped into orders.
The scientific name of an organism consists of two words - the generic name and the
specific name. This system of naming insects is called the binomial system of
nomenclature.
Insect orders
Insects are among the most abundant and successful of terrestrial animals. They
include about three-fourths of all described species of animals and have become
adapted to a wide range of environments. No other group of living creatures has such
variety of form, colour, function and habitat. The classification of insects into various
orders is based on the presence or absence of wings, wing venation, the type of
metamorphosis, the type of mouth parts, the characters of antennae, tarsi, etc. Thus
we have:
Class INSECTA
Sub-class APTERYGOTA
(Wingless)
Sub-class PTERYGOTA
(Winged)
There are four orders in Apterygota, viz:
1. Collembola (Springtails)
2. Diplura
3. Protura
4. *Thysanura (Silverfish)
Entomology handout
Page 9
Here, none of them are of economic importance, except silverfish, which occasionally
damage book-bindings. The subclass PTERYGOTA is further divided into two
groups as:
PTERYGOTA
EXOPTERYGOTA
ENDOPTERYGOTA
exo=external; endo=internal
In Exopterygota, the wings develop externally and the young ones are called nymphs
and metamorphosis is in-complete (Hemimetabolous). The following orders are
included in this division:
5. Ephemeroptera (Mayflies)
6. Odonata (Dragonflies)
7. Blattodea (Cockroaches)
8. Isoptera (Termites)
9. Mantodea (Mantids)
10. Zoraptera
11. Gryllablattodea
12. Dermaptera (Earwigs)
13. Plecoptera (Stoneflies)
14* Orthoptera (Grasshoppers, Crickets etc.)
15. Phasmatodea (Stick insects)
16. Embioptera (Web-spinners)
17. Psocoptera (Psocids, Book lice)
18. Anoplura (Sucking lice)
19. Mallophaga (Biting lice)
20* Hemiptera (Bugs)
21* Thysanoptera (Thrips)
In Endopterygota, the development of wings occurs internally and transformation
from larva to adult form occurs during a quiescent pupal stage. They undergo
complete metamorphosis (Holometabolous). The following orders are included in
this division:
22.
23.
24*
25.
Megaloptera (Alder flies)
Neuroptera (Lace wings, Antlions)
Coleoptera (Beetles)
Strepsiptera (Stylops)
10
26.
27.
28*
29.
30*
31*
Mecoptera (Scorpion-flies)
Siphonaptera (Fleas)
Diptera (Flies, Mosquitoes)
Trichoptera (Caddisflies)
Lepidoptera (Moths, Butterflies)
Hymenoptera (Wasps, Bees, Ants)
Insect orders of agricultural importance
ORTHOPTERA: Includes grasshoppers, crickets, etc. Orthopterans have chewing
mouth types in both adult and immature stage. Most orthopterans have two pairs of
wings, the forewings being thickened and of leathery texture are called tegmina. The
hind wings are large and fanlike and are folded beneath the tegmina when not in use.
They have thread-like, filiform antennae. The hind legs are usually enlarged for
jumping.
THYSANOPTERA: (Thrips) - Thrips are small or minute insects, and have a rasping
- sucking mouth type. Many species are wingless but when wings are present, they
are long, narrow and fringed with hairs. Many species of thrips are phytophagous,
causing damage to a variety of plants.
HEMIPTERA: Hemipterans have piercing and sucking mouth type. The fore-wings
are called hemelytra and are normally held flat over the abdomen when at rest. The
basal portions of these wings are hardened in texture, while the apical portions are
membranous. The hind wings are membranous and folded beneath the hemelytra.
They have a segmented beak which arises ventrally from the front or anterior region
of the head.
HOMOPTERA: They have piercing and sucking mouth parts. The fore-wings are
uniformly membranous or slightly thickened and the wings are held roof-like or tentlike over their bodies when at rest. This order also includes wingless and short wing
insects. Their segmented beak arises ventrally from the posterior portion of the head.
The order includes aphids, hoppers, mealy bugs and scale insects.
COLEOPTERA: These are the beetles characterized by having fore-wings which are
thickened and hardened into elytra, which meet along the mid-lines of the dorsal
surface and which are used to protect the delicate, folded hind wings. Beetles have
chewing mouth types in both the immature and adult stages. This is the largest order
in the animal kingdom and the group exhibits great diversity of forms and habits.
Included in this order are a variety of harmful as well as beneficial insects.
LEPIDOPTERA: These are the moths and butterflies. Lepidopteran larvae have
chewing mouth types, while some adults have vestigial or non-functioning mouth
types and do not feed. Most adults, however, have a long coiled proboscis which is
used for siphoning plant nectar. They have two pairs of membranous wings and the
body and appendages are clothed in broad scales. The immature stages of
Lepidoptera, called caterpillars, can cause considerable damage by their feeding.
Entomology handout
Page 11
DIPTERA: These are the true flies, with a single pair of membranous wings, the hindwings being modified into club-shaped halteres. There is a variety of feeding habits
and mouth types associated with members of this order. Adult Diptera may have
sponging, lapping or piercing-sucking mouth types. Dipteran larvae are legless and
have a chewing mouth type.
HYMENOPTERA: This order includes sawflies, wasps, bees and ants. Larval
hymenoptera generally have a chewing mouth type. Adults have chewing mouth
parts but this may again be modified for specific functions. Only a few species from
this order are considered to be of economic importance but the majority of them are
beneficial insects
12
Insect morphology
Head
The head of an insect is composed of a
series of segments, which are
specialized for food gathering and
manipulation, sensory perception, and
neural integration. The head bears the
eyes (compound eyes and ocelli),
antennae, and mouthparts.
The
anterior part of the head is the frons.
The anterior area below the dorsum of
the head, between and behind the eyes
is the vertex. The area below the
compound eye, on the side of the head,
is the gena. The liplike sclerite is the
clypeus. The principle structures of an
insect head are given in figure 1.
Fig: 1 Principle parts of in insect head.
Source: http://basicentomology.ifas.ufl.edu/lab5.doc
Antennae
The antennae are the sensory organ of smell touch and hearing (auditory) in insects. It
is with the help of antenna that insects are able to locate food, find their mates, detect
danger, feel and find their way. The specialisation of the antenna for different
functions may vary from one type of insect to the other. For e.g. antenna of houseflies
have a strong sense of smell and that is why they can appear from anywhere if there is
a rotten smell of meat. The shape, size and length of antenna vary so much.
Cockroaches have very long antenna whereas the antenna of houseflies no matter how
big in size can hardly be seen. Depending upon the shape, antenna can be filiform
(thread-like), clavate (clubshaped), pectinate (comb-like), bipectinate (double comb
like), plumose (feather-like), serrated (sawtooth-like), lamellate (plate-like),
monoliform (bead-like), aristate (pouch-like).
Antennal segments
The paired antennae are made up of a number of individual joints. The first antennal
segment (closest to the head) is called the scape. The second antennal segment is
called the pedicel and the remainder of the antenna is collectively called the
flagellum.
The basic form of antenna is filiform. In this type there are many segments that are
more or less equal in size. Filiform antennae are seen in a wide variety of groups, such
as Dragonflies, Grasshoppers and Crickets, Book Lice, Biting Lice, Scorpion Flies
and Beetles. The length and number of joints varies much between them.
Entomology handout
Page 13
Types of antennae:
Name
Appearance
Example(s)
Setaceous -- bristle-like
Dragonflies
Filiform -- thread-like
Ground beetles and
Cockroaches
Moniliform -- bead-like
Termites
Serrate -- sawtoothed
Click beetles
Clavate -- gradually clubbed
Carrion beetles
Capitate -- abruptly clubbed
Butterflies
Lamellate -- nested plates
Scarab beetles
Pectinate -- comb-like
Fire-colored beetles
and
Male glow-worms
Plumose -- brush-like
Mosquitoes
Geniculate -- elbowed
Weevils and Ants
Aristate -- pouch-like with
lateral bristle
House flies
14
Eyes
Insects have usually 2 types of eyes. The pair of big eyes that are prominently seen in
most insects are known as the compound eyes. It is so named because of the fact that
the eyes are made of many units of photo receptors that are each individually
functioning like our human eye. These visual units that make up the compound eyes
are known as ommatidia (ommatidium sing.). There may be up to 30,000 ommatidia
in a compound eye. The number of ommatidium however varies from insect to insect
depending upon their habit. The predatory insects have very powerful eyes which
mean the number of ommatidia is very high. Insects like worker ants have very few
ommatidia. This type of eye gives less resolution than the vertebrate eye, but it gives
acute perception of movement which is important in flight.
Besides the compound eyes, insects do have simple eyes called ocelli, on their
forehead. They are less apparent and are seen only as dark shining patches (usually 3)
of epidermal cells. Higher insects have both types of eyes where as lower insects and
larvae have simple eyes only. They are not as sensitive as the compound eyes but can
detect the changes in the illumination or intensity of light. For example it can alert the
insect if a shadow of a predator falls on it. Cut worms which are nocturnal in habit
probably depend on these simple eyes.
Entomology handout
Page 15
Mouthparts
The most important way in which insects inflict losses and injury upon man and his
possessions is by eating or feeding. Since insects feed in various ways, it is evident
that knowledge of insect mouth parts is of prime importance in the study of
entomology. The mouth part of an insect can be classified in accordance with their
function. According to this scheme there are those are those intended for biting and
chewing (Mandibulate) like in grasshoppers, crickets, cockroaches, lacewings and
beetles; those that are primarily used for sucking liquids (Haustellate) like in
stinkbugs, aphids, mosquitoes, houseflies.
1. Mandibulate
Biting-chewing
2. Haustellate
a) Stylet
Piercing-sucking
b) Non-stylate
Siphoning
Sponging
Chewing-lapping
Rasping-sucking
Stylets are needle-like projections used to penetrate plant and animal tissue. The
modified mandibles, maxilla, and hypopharynx form the stylets and the feeding tube.
After piercing solid tissue, insects use the modified mouthparts to suck liquids from
the host.
1. Madibulate type- Biting-chewing mouthpart
Source: http://www.ndsu.edu/entomology/topics/heads.htm
16
The main parts of this type are the
(1) Labrum - an unpaired, flap-like structure hinges to its upper margin to the lower
edge of the clypeus. It is located in front of (or above, depending on the direction the
head points) the oral cavity and serve as an upper "lip" and moves longitudinally.
(2) Mandibles (upper jaws) – is a pair of highly sclerotised, horny, usually large nonsegmented structures found immediately behind (or below) the labrum. They
articulate on the distal margins of the genae. The mandibles move at right angles to
the body. They are used for biting, chewing and severing food.
(3) Maxillae - (lower jaw) is a pair of segmented structures situated immediately
behind or below the mandible. The maxillae moves at right angles to the body and
possess segmented palps.
(4) Labium – (the lower lip) is an unpaired structure serving as a lower lip and
closing the oral cavity from below or behind; it moves longitudinally and possesses a
pair of segmented palps.
(5) Hypopharynx - this is an unpaired structure, otherwise known as the tongue,
which occupies a portion of the oral cavity; it is located more or less in the center of
this space and near the base of the labium.
Fig. 11 Different parts of a mandubulate type mouth.
2. Haustellate type of mouthpart is basically a modification of the simple bitingchewing type.
Haustellate mouthpart can be broken down into two subgroups: those that possess
stylets and those that do not.
a) Piercing-sucking type of mouthpart present in stink bugs is an example of
haustellate type with stylets. Mandibles and maxillae are formed into stylets
which are enclosed by the labium. Once the stylets penetrate, a secretion is
injected to dissolve tissue, act as a toxin in predacious species, or as
anticoagulant for mosquitoes.
Entomology handout
Page 17
b) Siphoning type: Those without stylets are unable to pierce tissues, and therefore
these insects must rely on easily accessible food sources such as nectar at the base of a
flower. One example of nonstylate mouthpart is the long siphoning proboscis of
butterflies and moths (Lepidoptera). When feeding the proboscis is uncoiled and
extended. Nectar is sucked up into the mouth or oral cavity. The proboscis is a
modified maxillae.
c) Sponging - Found in adults of specialized flies. During feeding the proboscis
(modified labium) is lowered and salivary secretions are pumped onto the food. The
dissolved or suspended food then moves by capillary action into the pseudotracheae
(sponge) and is ingested. There may be sharp teeth on the pseudotracheae to rasp flesh
and draw up blood. The labella is the fleshy distal end of the labium that functions as
a sponge-like organ to sop up liquids.
d) Chewing-Lapping - Adult honeybees and bumble bees. Mouthparts are modified
18
to utilize liquid food, honey and nectar. A central "tongue" is used to draw liquid into
the body. The mandibles are not used for feeding but function to cut floral tissue to
gain access to nectar, for defense, and for manipulating wax.
e) Rasping-sucking – Thrips have rasping sucking type of mouthpart. (To rasp
means to scrape with a coarse file). The mandibles which are asymmetrical injure
the tissue and the cell sap oozing out is being sucked
The insect thorax
The insect thorax is box-like with dorsal, ventral and lateral sclerites. The dorsal
sclerites are collectively called the notum (pronotum, mesonotum, and metanotum)
which may be further subdivided into an anterior scutum and a posterior
scutellum. The ventral sclerites are called the sternum (prosternum, mesosternum,
and metasternum). Each sternum is divided into several plates, called sternites. The
lateral sclerites are called the pleuron.
The thorax is divided into three parts and from front to back; these segments are
named as follows:
(1) Prothorax - the first of the three (hence Pro-) and bearing the first pair of true
legs; wings are never present on this portion of the thorax. The top plate of the
segment, the Pronotum, is in most winged insects are rather highly specialized and is
usually enlarged to some extent.
(2) Mesothorax - (meso= middle) this is the middle of the three thoracic ringsegments; it bears the second pair of true legs and the first pair of wings when two
pairs are present. If only one pair of wings is present, as is the case with the flies, then
that single pair is located on this segment of the thorax. In other species (i.e., scale
insects, the males have one pair of wings on the metathorax!). One pair of spiracles is
often found on this segment. In most insects, usually no spiracles are found on the 1st
or third thoracic segments.
(3) Metathorax - (Meta-last) this is the third and last of the thoracic segments; it
bears the third pair of true legs and the second pair of wings, when they are present. A
Entomology handout
Page 19
pair of thin knobbed projections (halters) takes the place of this second pair of wings
in the Diptera.
Legs
The legs, named from the anterior, are the fore, mid and hind legs. Each leg consists
of four main parts - the coxa, the femur, the tibia and the tarsus (plural: tarsi) - with
a small, often inconspicuous segment between the coxa and femur, called the
trochanter. The tarsus is collectively composed of 2 to 5 smaller tarsomeres. The last
tarsomere usually has a pair of claws and often 2 or 3 tarsal pads- the arolium.
Figure: 12 parts of insect legs
(source: http://basicentomology.ifas.ufl.edu/lab5.)
Insect legs have been variously adapted for running, jumping, grasping, swimming or
digging. An examination of insect legs can often tell much about the habits of the
insect. Some of the insect leg modifications are






Unmodified legs are used for walking and are called ambulatory
Legs modified for running are called cursorial.
Digging legs are called fossorial
Swimming legs are called natatorial.
Jumping legs are called saltorial.
Grasping legs are called raptorial.
Wings
(Source: http://www.cals.ncsu.edu/course/ent425/tutorial/wings.html)
Insects are the only invertebrates that can fly and their wings are unique
among all animals. They are outgrowths of the body wall rather than
modified appendages. The wings may be membranous, parchment-like,
heavily sclerotized, fringed with long hairs, or covered with scales. Most
insects have two pairs of wings -- one pair on the mesothorax and one pair on
the metathorax (never on the prothorax). Wings serve not only as organs of
flight, but also may be adapted variously as protective covers (Coleoptera
and Dermaptera), thermal collectors (Lepidoptera), gyroscopic stabilizers
20
(Diptera), sound producers (Orthoptera), or visual cues for species
recognition and sexual contact (Lepidoptera).
Basically, insect wings are very simple flap-like extensions of the body wall,
with an upper and lower membrane between which run hollow tubes known
as the veins which give rigidity and support. In most cases, a characteristic
network of veins runs throughout the wing tissue. These veins are extensions
of the body's circulatory system. They are filled with hemolymph and
contain a tracheal tube and a nerve. The venation (arrangement of veins)
varies from very simple to extremely complex and is an important character
in identification of many orders, families and genera. In membranous wings,
the veins provide strength and reinforcement during flight. Wing shape,
texture, and venation are quite distinctive among the insect taxa and therefore
highly useful as aids for identification. Wings become functional only in the
adult stage.
Wing Venation:
Costa (C) -- the leading edge of the wing
Subcosta (Sc) -- second longitudinal vein (behind the costa), typically
unbranched
Radius (R) -- third longitudinal vein, one to five branches reach the wing
margin
Media (M) -- fourth longitudinal vein, one to four branches reach the wing
margin
Cubitus (Cu) -- fifth longitudinal vein, one to three branches reach the wing
margin
Anal veins (A1, A2, A3) -- unbranched veins behind the cubitus
Names of crossveins are based on their position relative to longitudinal veins:
Entomology handout
Page 21
c-sc crossveins run between the costa and subcosta
r crossveins run bewteen adjacent branches of the radius
r-m crossveins run between the radius and media
m-cu crossveins run between the media and cubitus
Wing adapations and modifications:
Insect wings have been modified in many ways; for example:





The wings of a moth are covered with minute scales which are often
brightly colored.
The fore wings of a beetle are hardened and form a protection (the
elytra) for the membranous hind wings.
Cockroaches and grasshoppers have leathery fore wings (Tegmina).
Some bugs have half-leathery, half-membranous fore wings
(hemelytra).
In flies, (Diptera), the hind wings have become modified to form
small balance organs, called halteres.
Characteristic
Appearance
Elytra -- hard,
sclerotized front
wings that serve
as protective
covers for
membranous
hind wings
Order(s)
Coleoptera
and
Dermaptera
Hemelytra -front wings that
are leathery or
parchment-like at
the base and
membranous
near the tip
Hemiptera:
Heteroptera
Tegmina -- front
wings that are
completely
leathery or
parchment-like in
texture
Orthoptera,
Blattodea,
and
Mantodea
22
Halteres -- small,
club-like hind
wings that serve
as gyroscopic
stabilizers during
flight
Diptera
Fringed wings -slender front and
hind wings with
long fringes of
hair
Thysanoptera
Hairy wings -front and hind
wings clothed
with setae
Trichoptera
Scaly wings -front and hind
wings covered
with flattened
setae (scales)
Lepidoptera
Hamuli -- tiny
hooks on hind
wing that hold
front and hind
wings together
Hymenoptera
Entomology handout
Page 23
Frenulum -Bristle near base
of hind wing that
holds front and
hind wings
together
Lepidoptera
Abdomen and external genitalia
The abdomen is the third and posterior region of the insect body. The abdomen of
adult insects contains no legs or wings and usually consists of 10 or 11 segments.
However, in many orders, reduction has occurred or the segments are concealed or
modified. Each segment of the abdomen consists of a dorsal sclerite, the tergum, and
a ventral sclerite, the sternum, joined to one another laterally by a pleural
membrane. In many adult insects, there is a spiracle (opening to the respiratory
system) near the pleural membrane on each side of the first eight abdominal
segments.
At the very back of the abdomen, the anus (rear opening of the digestive system) is
nestled between three protective sclerites: a dorsal epiproct and a pair of lateral
paraprocts. A pair of sensory organs, the cerci, may be located near the anterior
margin of the paraprocts. These structures are tactile (touch) receptors. They are
usually regarded as a "primitive" trait because they are absent in the hemipteroid and
holometabolous orders.
Terminally the abdomen bears the external genitaliaThe insect's genital opening lies
just below the anus: it is surrounded by specialized sclerites that form the external
genitalia. In females, paired appendages of the eighth and ninth abdominal segment
fit together to form an egg-laying mechanism called the ovipositor. A pair of cerci is
also present at the end of the abdomen.
These have a sensory function.
24
In males, the genital opening is usually enclosed in a tube-like aedeagus which enters
the female's body during copulation (like a penis). The external genitalia may also
include other sclerites (e.g. subgenital plate, claspers, styli, etc.) that facilitate mating
or egg-laying. The structure of these genital sclerites differs from species to species
to the extent that it usually prevents inter-species hybridization and also serves as a
valuable identification tool for insect taxonomists.
Other abdominal structures may also be present in some insects. These include:








Pincers -- In Dermaptera (earwigs), the cerci are heavily sclerotized and
forceps-like. They are used mostly for defense, but also during courtship, and
sometimes to help in folding the wings.
Median caudal filament -- a thread-like projection arising from the center of
the last abdominal segment (between the cerci). This structure is found only
in "primitive" orders (e.g. Diplura, Thysanura, Ephemeroptera).
Cornicles -- paired secretory structures located dorsally on the abdomen of
aphids. The cornicles produce substances that repel predators or elicit caregiving behavior by symbiotic ants.
Abdominal prolegs -- fleshy, locomotory appendages found only in the larvae
of certain orders (notably Lepidoptera, but also Mecoptera and some
Hymenoptera).
Sting -- a modified ovipositor, found only in the females of aculeate
Hymenoptera (ants, bees, and predatory wasps).
Abdominal gills -- respiratory organs found in the nymphs (naiads) of certain
aquatic insects. In Ephemeroptera (mayflies), paired gills are located along
the sides of each abdominal segment; in Odonata (damselflies), the gills are
attached to the end of the abdomen.
Furcula -- the "springtail" jumping organ found in Collembola on the ventral
side of the fifth abdominal segment. A clasp (the tenaculum) on the third
abdominal segment holds the springtail in its "cocked" position.
Collophore -- a fleshy, peg-like structure found in Collembola on the ventral
side of the first abdominal segment. It appears to maintain homeostasis by
regulating absorption of water from the environment.
Entomology handout
Page 25
Reproduction in insects
How do insects find their mates?
Insects use different ways in order to attract their mating partners. Insects use sound
(Example crickets, grasshoppers and cicadas), smell (Moths), colour (Moths and
butterflies) and pheromones (Moths). Pheromone is a chemical which is produced by
living organisms that transmits message to other members of the same species.
Types of reproduction in insects
Reproduction in insects can take a wide variety of forms, often very complex. Some
can switch their type of reproduction during their life cycle based on environmental
triggers. Others reproduce the same way throughout their life history. The basic theme
and some of the variations are described below.
Sexual reproduction: The standard model for reproduction is where males and
females occur throughout the life cycle, and each produces a germ cell (egg and
sperm, respectively). The male inseminates the female during mating. The female
often stores sperm in special pouches in her abdomen called spermathecae (singular,
spermatheca). The eggs are fertilized within the female's body, producing an embryo.
Eggs are deposited on a host. They hatch and develop into either male or female
offspring.
Parthenogenesis: This is asexual reproduction, where eggs grow and develop without
fertilization. There are several variations of parthenogenesis. Arrhenotokous
parthenogenesis is where unfertilized eggs produce only males. In deuterotokous
parthenogenesis, both males and females are produced from unfertilized eggs. In
thelyotokous reproduction, unfertilized eggs produce only females.
Viviparity: Most insects deposit eggs that hatch into nymphs or larvae, a process
called oviparity, but some insects bear living young. A common example is aphids,
which are viviparous during part of their life cycle. A variation is ovoviviparity,
where eggs are held within the female's body, where they hatch, and the young are
born live.
Polyembryony: This is where two or more embryos develop from a single egg, as in
the parasitic Hymenoptera, such as braconid, encyrtid, and dryinid wasps.
Insect growth and development
Definitions1
Chrysalis - a butterfly pupa, not enclosed in a cocoon, a pupa without a
protective cover.
Cocoon - a case formed partly or wholly of silk secreted by the larva and in
which pupation occurs, a protective cover.
1
http://www.ndsu.nodak.edu/entomology/topics/growth.htm
26
Instar
Larva
Molting
Nymph
Pupa
Stage
- form of an insect between successive molts, the first instar being
the stage between emerging from the egg and the first molt.
- (pl. larvae) immature stage between the egg and pupa in insects
with complete metamorphosis or, sometimes, between egg and
adult in insects with incomplete metamorphosis.
- the acting of shedding the cuticle or insect skin, shedding of the
exoskeleton .
- immature stage of insects with incomplete metamorphosis.
- (pl. pupae) the third, inactive stage of insects with complete
metamorphosis, the transition stage between the larval and adult
stages. Usually non-mobile.
- any definite period in the development of an insect, e.g.. the egg
stage, nymphal or larval stage, pupal stage, adult stage. The
number of nymphal or larval stages is variable.
Insect life cycle
Life cycle is the chain of biological events that occurs during the lifetime of an
individual insect. The cycle usually begins with deposition of egg and ends with egg
lying by the adult.
Egg: Eggs come in many shapes, sizes, and colors. They might be deposited on or in
the ground, the roots, the stems, the leaves, or the flowers. When the eggs hatch the
new insect is called a larva. The plural of larva is larvae.
Larva: The larva seldom looks like the adult it will become. Some common larval
forms are the maggot, grub worm, nymph and caterpillar. As the larva grows it must
shed its old skin from time to time. This is called molting or ecdysis. From hatching
to the first molt the larva is said to be in its 1st instar stage. After molting the first
time the larva enters its second instar stage, and so on (fig. 13). Different insects have
different numbers of instars, but eventually the larva is fully grown and ready to
pupate.
Fig.13 Stages in development of an insect to adult insect
Entomology handout
Page 27
Pupa: The pupa is the life stage between larva and adult. In this stage the insect does
not feed, and is in a quiescent state. Most pupae are found hidden and protected
habitats. Some usually construct some kind of shelter (cocoon) to pupate in. This
"cocoon" might be made from soil particles, silk, chewed seeds, chewed plant
material, ground litter, or combinations. After pupation the adult emerges to mate and
to lay eggs. The figure below illustrates the life cycle of a fly.
Figure: 14. An example of insect life cycle showing complete metamorphosis (Source:
http://www.ndsu.nodak.edu/entomology/topics/growth.htm)
Metamorphosis
The majority of insects start life in the form of a fertilized egg laid by a female on
plants or in the ground. After hatching of the egg the developing young one undergoes
a series of changes in size and structure before becoming adult. Each time an insect
makes a change into the next growth stage, it has to molt (shed) its skin. After each
molt, the insect becomes a little larger and somewhat different in form until it reaches
the adult stage. After it reaches the adult stage, it does not molt or grow any more. To
the series of changes which takes place in the life history of an insect the term
metamorphosis has been applied. There are four kinds of metamorphosis, complete
(butterflies), gradual (grasshoppers), incomplete (dragonflies) and no
metamorphosis (Silverfish). The exact style of metamorphosis is not the same for
all insects, but insects in the same order have the same style of metamorphosis.
Ametabolous development: Some orders of insects are said to have no
metamorphosis (Ametabolous development) because there is little or no difference
in appearance between the young stages and the adult except for size (Fig.14). The
28
no-metamorphosis model is found in primitively wingless insects (Subclass
Apterygota). Suitable examples are primitive insects such as silverfish (Thysanura).
Fig. 15 typical development of an aterygote insect with no metamorphosis
Source: http://www.cals.ncsu.edu/course/ent525/trans.html
Gradual metamorphosis (Paurometabolous development): The life cycle of
insects with gradual metamorphosis have three life stages (Fig. 16): egg, nymph and
adult. Nymphs resemble the adult except that their body parts are out of proportion
with each other, and they do not have fully developed wings and external genetalia.
With each molt, the nymphs gradually develop wings and take on the body
proportions of an adult. Nymphs have the same type of mouthparts as the adult, and
they both feed on the same kind of food.
Fig.16 The life cycle of a plant bug.
Source: http://www.cals.ncsu.edu/course/ent525/trans.html
Incomplete metamorphosis (Hemimetabolous development) is somewhat like
gradual metamorphosis and also has three life stages: egg, naiads and adult.
However, the adult insect with incomplete metamorphosis lays its eggs in or near
Entomology handout
Page 29
water and the naiads develop in water. The adults are flying insects that live out of
water. Naiads and adults therefore do not eat the same kind of food. Naiads have
chewing mouthparts, but the adults have differently shaped chewing mouthparts or no
functional mouthparts. The naiad and the adult usually differ a lot in appearance
although the naiads gradually develop wings.
Complete metamorphosis (Holometabolous development): It has four distinct
form stages: egg, larvae, pupa and adult (Fig.17). The larval stages do not look like
the adult at all, and they are often worm-like. Larvae often have different mouthparts
and food habits than the adult, and they often live in places different from the adult.
Larvae molt several times and get a little larger with each molt, but there is no gradual
development of wings or other adult characteristics. When a fully grown larva molts,
it changes into a pupa. The pupa usually does not eat or move around much, but a lot
of internal changes take place. When the pupa has made all its internal changes, its
skin splits and the fully formed adult emerges. Most insects with complete
metamorphosis are winged in the adult stage. The adults do not molt or grow any
more. Little flies or beetles, for instance, do not grow to become larger. Flies
(Diptera), beetles (Coleoptera), wasps (Hymenoptera) and butterflies (Lepidoptera),
have holometabolic life cycles.
Fig. 17 Complete metamorphosis
Source: http://www.cals.ncsu.edu/course/ent525/trans.html
Insect seasonal cycles
The progression of one or more life cycles occurring during a 1-year period is termed
as the insect seasonal cycles. Seasonal cycles are very important to the survival of the
insects because most environments of which insects are part of undergo annual colds.
Therefore, to achieve success, insects have evolved ways to time their activities to
take advantage on environmental resources and avoid unfavorable extremes.
30
Knowledge of patterns in seasonal cycles and the timing of important biological
events relative to environmental cycles are crucial when attempting to reduce pest
damage.
Seasonal cycle can be grouped according to the number of generations that occur in a
year; this number is referred to as a population’s voltinity. Voltinity types are
univoltine, multivoltine, and delayed voltine.
Larval forms
The larval form is highly variable in insects, but there are similarities in the general
structure to permit a classification of type that is useful in describing their appearance.
(1) Campodeiform larvae have a flattened body with long legs, usually with
filaments on the end of the abdomen. Larvae of diving beetles in the family
Dytiscidae and many other beetles, Neuroptera, and Trichoptera are typical examples.
(2) Carabiform larvae are similar to the campodeiform type, but the legs are shorter
and filaments are lacking on the end of the body. They receive their name from the
larvae of carabid beetles. Chrysomelid beetle larvae are of the same type.
(3) Eruciform larvae (Polypod larvae) are cylindrical; they have a well-formed head,
3 pair of sclerotised and jointed thoracic legs, and fleshy abdominal prolegs.
However, several species representing the various orders of insects do not have such
distinguishing features. Larvae of Lepidoptera and sawflies are typical
(4) Scarabaeiform larvae (Oligopod larvae) are C-shaped, have a well developed
head, and usually possess thoracic legs but lack prolegs. The type is named after
larvae of scarabaeid beetles (dung beetles, May beetles) and is also represented by the
larvae of weevils and furniture beetles.
(5) Elateriform larvae are cylindrical, smooth, and relatively tough-skinned larvae
with short legs. They are named after larvae of elaterid or click beetles (wireworms).
Larvae in the beetle family Tenebrionidae also have this appearance.
(6) Platyform larvae are broad and flat with legs short or absent. This type is not
common, but examples are found among larvae of some syrphid flies, certain
caterpillars, and blister beetles.
(7) Vermiform or wormlike larvae (Apod larvae) are cylindrical and elongate,
without appendages of locomotion. This form is represented by the larvae of higher
Diptera (maggots), some woodboring beetles, fleas, and higher Hymenoptera,
including the honey bee.
Entomology handout
Page 31
Appearance
Larval
Type
Eruciform
Campodeifo
rm
Scarabaeifor
m
Common
Name
Caterpillar
Crawler
Description
Body cylindrical with
short thoracic legs and 210 pairs of fleshy
abdominal prolegs
Examples
Moths
and
butterflies
Elongated, flattened body
Lady
with prominent antennae
beetle,
and/or cerci. Thoracic legs
lacewing
adapted for running
Body robust and "C"shaped with no abdominal
White grub
prolegs and short thoracic
legs
Elateriform
Wireworm
Body long, smooth, and
cylindrical with hard
exoskeleton and very
short thoracic legs
Vermiform
Maggot
Body fleshy, worm-like.
No head capsule or
walking legs
June
beetle,
dung
beetle
Click
beetle,
Flour
beetle
House fly,
flesh fly
Pupal forms
Pupal forms may be classified by means of the appearance of developing appendages.
(1) In obtect pupae the appendages are close to the body, held there by a tight-fitting
outer envelope. They appear almost to be glued to the body proper. Pupae of this type
are found in Lepidoptera and many Coleoptera, as well as the less advanced Diptera.
The obtect pupa of butterflies is a common example.
(2) Exarate pupae refer to those species that undergoes complete metamorphosis
where their appendages (antennae, legs, and wings) appear to be free from the body
proper. The bees and wasps of the Hymenoptera are common examples.
(3) Co-arctate pupae are represented by those that use the exuviae (cast exoskeketon)
of the last larval instar as the container or place for pupal development. In this
instance, neither the outline nor the actual structures are visible. The flies are
examples of this type of pupation.
32
Pupae can be grouped into one of three categories based on physical appearance:
Appearance
Pupal
Type
Common
Name
Obtect
Chrysalis
Exarate
None
Coarctate
Puparium
Entomology handout
Description
Examples
Developing appendages
(antennae, wings, legs, etc.)
held tightly against the body by Butterflies
a shell-like casing. Often found and moths
enclosed within a silken
cocoon.
All developing appendages
free and visible externally
Beetles,
Lacewings
Body encased within the hard
exoskeleton of the next-to-last
larval instar
Flies
Page 33
Insect Collection
Purpose of collecting and preserving insects
There must be a purpose for collecting insects. Some of the reasons for collecting and
preserving insects are:
1. For studying the insect biology, lifecycle and biodiversity
Because of the damage inflicted by pest species, increased knowledge of these
organisms has the potential to save lives and money. Insects are collected for
studying the details and gaining a better understanding of their biology and life
cycles. Insects are sometimes collected for recording the biodiversity.
Extension agents will come across several species of pests in their geogs. For
better understanding of the pest biology and lifecycle, they must make an effort to
identify the pest. As the first step towards identification, proper collection, setting
and preservation of the pest species is a must.
2. For identification( species determination)
a) Newly detected insects
Correct identification (knowing the scientific name) of a newly detected pest or
disease vector is the key to all known information about the morphology,
behaviour and life history, and the potential threat to human welfare. Insects are
collected for species determination so that it is convenient for finding out more
information.
b) Small insects that are difficult to identify
The behaviour of insects can be observed most easily in their natural
environments. However, many species, especially the smaller ones, must be
collected and properly preserved before they can be identified. Because correct
identification seldom is easy, it is important that specimens be preserved in the
best condition possible. Therefore preservation is highly important.
c) Pest outbreak reports
During pest outbreaks in the geogs, extension agents need to report to their
superiors on the type of pest that is responsible for the outbreak. It is very useful
to collect the pest and submit to the concerned authorities for identification. Such
collections submitted for identification need to be well set and preserved.
Therefore extension agents need to have the required skills of setting and
preserving pest specimens.
3. Insect collection for future reference
In a geog extension centre, insect pests must be collected, identified and preserved
for the purpose of educating farmers (farmer trainings) on crop pest identification.
A good reference collection is a valuable resource for the extension agent. It
makes future identification efforts less cumbersome. In a geog extension centre, it
is of utmost importance to maintain a reference collection of pest species for all
the crops grown in the locality.
4. Insect collection as a hobby.
34
There are people who love to collect insects and preserve them just for the love of
it. Moths and butterflies are collected for their beautiful colour and wing patterns.
Some larva are collected for their giant size and weird body ornamentations. Some
giant beetles are collected and sold as pets.
Why insects have to be adequately set, preserved and correctly labelled?
The identification of a particular insect usually requires examination of minute details
of its anatomy with the aid of a hand lens or microscope. Some specimens may
require dissection or even study with the electron microscope. If these details on a
specimen are concealed, missing, or destroyed because of improper handling or
preservation, identification is made difficult or impossible, and information about the
species to which it belongs cannot be made available. Therefore, adequate
preservation and proper labelling of specimens are essential to their identification.
What is the relevance of the knowledge and skill of insect collection and
preservation in the field of agriculture extension?
For diagnostic purpose: Correct identification or species determination is the key to
all known knowledge and information about the pest in question. To 2be able to
correctly identify insect pests, the morphological features of the collected specimens
should neither be concealed, nor destroyed. If extension agents need to send the
specimens for identification by the entomologists, they need to send a specimen that is
well set, preserved and packaged. Such skills can be learnt through practice.
Building a reference collection for the geog extension centre: If there is a reference
collection at the geog extension centre, it is not just helpful to you for using as
farmers training aid but more importantly, the person who is going to relieve you
upon your transfer will have great benefits. Learning the skills of collecting and
preserving insects would help you to build your own reference collection at the geog
extension centre.
Insect collection equipment and materials
The basic equipment necessary for field collecting is an insect net, one or more
storage boxes, pins, pinning blocks, spreading boards, light and pitfall traps, killing
jars, killing and preserving chemicals, several vials of assorted sizes, plastic bags and
assorted containers.
1. Killing jars: Insects must be killed before pinning and mounting. Killing jars are
used as a sort of “small scale fumigation” to kill collected insects as rapidly as
possible, using a liquid fumigant or killing agent (ethyl acetate) that produces a toxic
atmosphere that the insect cannot breathe.
2
David L. Keith and Tiffany Heng-Moss. Collecting insects. Retrieved Aug 18, 2009, from
http://entomology.unl.edu/tmh/ent115/labs/collecting.htm
Entomology handout
Page 35
When placed in the killing jar, insects often close their spiracles, but eventually they
must open them. The process may take several minutes for smaller insects or up to a
half hour or more for larger specimens. Because large, hard-bodied insects such as
beetles die slowly and may damage other insects placed in the same killing jar, you
will need more than one jar.
It is possible to make suitable killing jars with nearly any glass jar used for jam or
jelly and baby food jars are especially handy. In the bottom of each jar, place about 1
to 1 1/2 inches of absorbent material, such as cotton, shredded newspaper, Plaster of
Paris or sawdust. If Plaster of Paris is used, pour it about 1 inch deep and allow it to
dry for at least 48 hours before use. With paper-or fiber-filled jars, cut a cardboard
circle just slightly larger than the inside diameter of the jar and push it into the
opening against the plaster in the bottom. Attach a label that says POISON to each jar
and store the jars out of reach of children (or irresponsible adults) until you are ready
to go collecting.
If a killing jar is not available, freezing is another way to kill insects. Simply place
your specimens in a plastic bag or small jar and put them in the freezer for an hour or
two. Do not handle them again until they are thawed or legs and antennae may break.
Insects, like food, left too long in the freezer for several days or weeks will desiccate
and remain dry and stiff, even when thawed. If pinned when dry, these insects will
break during handling and wings, especially of Lepidoptera, will be impossible to
spread.
Pinching the thorax of large butterflies or moths before placing them in the killing jar
will prevent them from flopping around and damaging the wings. Squeeze them for
20-30 seconds between thumb and index finger and put them in the killing jar. This
procedure stuns the insects so they do not flutter once inside the jar. Remove
butterflies and moths from the killing jar fairly soon so their wings do not become
soaked with killing agent.
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2. Relaxing jars: We recognize that while insects should be pinned on the same day
they were collected, this is not always possible. So before pinning these specimens
left in the killing jar or freezer too long, to restore their flexibility, it is necessary to
“relax” them. By placing them in a relaxing jar at high humidity for a few days we
can restore their flexibility enough to allow pinning without damage to the specimens.
A relaxing jar can be made by placing some absorbent material such as newspaper,
sand or cotton in the bottom of a glass jar and cut a blotting paper disk to fit tightly
inside. Moisten the material with water and add a drop or two of ethyl acetate, phenol
or laundry beach to prevent mold. Place insects on the paper, close the jar tightly and
let it sit for about 2-3 days. Check the jar. If the insects are flexible, mount them
immediately. If the specimens are still too stiff, keep them in the relaxer for a few
more days, but watch them carefully. Insects will mold and decompose if held in the
relaxer too long.
3. Collecting Net (Aerial nets and sweep nets): Basically, a collecting net is
composed of some sort of net bag made of cloth or fine mesh that is attached to a wire
hoop, which is affixed to a wooden or metal pole. Aerial nets typically have net bags
that are composed entirely of some type of meshed material and often have a
lightweight handle. Aerial net bags are usually white in color, but black net bags are
also available. They are most useful for catching select insects that may be flying
through the air or perched on something (such as dragonflies, butterflies, bees, or
wasps). Aerial nets with larger hoops are better for collecting large and fast moving
insects such as dragonflies and butterflies, while those with small hoops are better for
bees, flies, wasps, and other smaller insects.
Sweep nets are usually made of a heavy material (such as canvas) that can be dragged
through dense vegetation without being damaged. They usually have heavier handles
than those on sweep nets as well. Sweep nets are used to sweep through vegetation to
collect random insects not easily seen. These nets are sometimes referred to as
“beating” nets
4. Aspirator: The aspirator is a suction device for collecting small insects which are
difficult (or hazardous) to capture with the fingers or with an insect net. Basically, it
consists of a large glass or plastic vial, a length of flexible rubber tubing, some rigid
plastic or metal tubing and a rubber stopper with 2 holes cut in it to receiving the
tubing. A small piece of cheesecloth or fine metal screen serves to seal the suction
tube on the inside so that insects are not sucked into the mouth. To collect small
insect the long tube is placed beside the insect and sucked sharply by mouth from the
shorter rubber tube.
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5. Light traps: Many types of insects are attracted to light and can be captured there
by hand. A light trap offers the advantage that it will continue to trap specimens
without being constantly watched by the collector. Insects are quite sensitive to
different types of light; therefore, more of certain types can be captured with “black”
(or ultraviolet) light as opposed to the regular “white” light given off by most standard
light bulbs. The difference in attractiveness of the two types of light is due to the
wave lengths produced by the two kinds of bulbs. Black light consists mainly of the
shorter wave lengths which are more attractive to night-flying moths, flies and
beetles. White light bulbs (producing mostly longer wave lengths) attract some moths
and other insects, but not as many as a black light.
6. Pitfall traps: A pitfall trap will catch many ground beetles and other insects that
live on or in the soil. It consists of a trap can that is buried in the soil, level with the
rim so that insects attracted to it will fall in. Once inside, it is difficult for them to get
out. Attractive bait in the bottom will increase the drawing power of the trap. Use
pieces of spoiled fruit, vegetables, excrement or meat. Cover the trap with a board
placed on small stones so insects can crawl under it and into the can. This
arrangement will protect the trap from wind and rain, but allow access to the insects
you want to catch. It will also help to hold insects inside the trap once they are caught.
Preserving insects
Hard-Bodied Insects
Since insects have a hard shell or exoskeleton and all of the soft parts are on the
inside, they tend to keep rather well after drying, even for long periods of time. Only a
small amount of maintenance is necessary to keep them in good condition.
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Soft-Bodied Insects
Many types of insects, including aphids, springtails, thrips, mayflies or silverfish, are
soft-bodied and cannot be pinned successfully. The same is true of many immature
insects such as caterpillars, beetle and wasp larvae and others. If placed on pins, most
soft-bodied insects will shrivel or decompose. Such insects must be preserved in
liquids in rubber-stoppered glass vials. However, prior to preserving soft-bodied
specimens for the long term, their color must be “fixed” or they may fade in some
cases or blacken in others. The “fixing” process prevents, reduces or delays color
change.
For the long term, insects are preserved in ethyl alcohol, usually of about 70 percent
concentration (70% alcohol, 30% water). However, it must be remembered that
alcohol is a dehydrator and removes water from the specimens preserved in it. These
problems can be largely prevented in either of two ways. The best way is to “fix” the
insect tissues and color by killing the specimens in boiling water. For smaller
specimens, simply dip them in boiling water for about 30 seconds and then transfer
them to 70 percent alcohol. Use more extended periods for large-bodied insects.
Specially designed and constructed container “Schmidt Boxes”, are required for long
term insect storage. Such boxes have tightly fittng lids which help prevent entry of
scavenger insects which feed on dead insect specimens. Wooden boxes can be used
for temporary storage of pinned insect specimens. The bottom of wooden boxes can
be lined with styrofoam material or cardboard to receive and hold the insect pins.
While wooden boxes are fine for temporary storage, they are poor over long periods
of time. For extended storage and for display, tighter containers are essential. Add
naphthalene crystals, placing them into a small container in one corner of each display
box to prevent damage to your specimens.
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Pinning, mounting and displaying insects3
Equipment required
Insect Pins. Special pins are needed to pin insects. They come in several sizes from
00 through 7, the size of the pin increasing with each number. Number 3 insect pins
are the best for most purposes.
Fig. 1. Insect pins
Fig. 2. Pinning block
Fig. 3 Pinning block(cross-section)
Pinning Block: Larger insects should be mounted using a wooden pinning block (Fig
b & C), a simple piece of equipment. A very small hole is bored almost through the
bottom in the middle of each step. A simpler pinning block can be made by drilling
three holes—1, 3/4, and 1/2 inch deep—into a small wooden block. Proper use of a
pinning block will result in an attractive collection with the insect, collection and
identification labels in uniform position. Note the dimensions of a pinning block in
the drawing below.
Spreading Board: Mounting butterflies and moths is a special technique that
requires a spreading board to do an attractive job. The spreading board is usually
made of soft pine with a piece of cork underneath the center groove to receive insect
pins.
Fig. Spreading board
Pinning Insects
The preferred way to display and study adult insects is to pin them into display boxes
using special insect pins. The pins are pushed through the thorax of the insects while
they are still fresh and the legs and antennae are placed in a natural position. This
allows the specimens to be handled and studied without damaging them. In pinning
insects always use special insect mounting pins that are specially treated to resist
rusting. Insect pins vary in size from 000 to number 8. The latter is the largest in
3
David L. Keith and Tiffany Heng-Moss. Collecting insects. Retrieved Aug 18, 2009, from
http://entomology.unl.edu/tmh/ent115/labs/collecting.htm.
40
diameter. Numbers 2 and 3 usually work the best for the amateur collector. A good
rule is to pin the insect slightly to the right side of the middle and down through the
area where the middle pair of legs is attached. Styrofoam is an excellent base for
positioning the legs so they will dry in the correct position. There is a slight variation
in the pinning of the different kinds of insects. The proper way to pin an insect
depends on the type of insect that you have collected. The following diagram (Fig.18)
illustrates the proper way to pin various orders of insects.
Note that the pin is usually just slightly to the right of the midline of the insect.
Specimens should also be level and squarely mounted on the pin as shown.
All insects must be pinned so that
they are straight on the pins. Do
not tilt the specimens on the pin.
The height of the specimen on the
pin will depend somewhat on the size of the insect; however, always keep the
distances from the top of the insect’s body to the head of the pin the same. Usually 1/3
of the pin should be above the upper
surface of the insect; this will allow enough room to permit handling specimens
without actually touching them. Specimens should be handled carefully to keep all
legs and antennae. A small amount of time spent positioning the legs and antennae
will dress up the collection.
Very small insects (less than 3/16 inch) should either be pinned with micro-pin or
glued on their right sides to tiny paper triangles. The latter procedure is called
pointing. When pointing, first push a regular insect pin (No. 2 or 3) through the butt
end of the triangle. Bend the tip of the paper triangle slightly downward with a
forceps and touch it to a tiny drop of glue or clear fingernail polish. Pick up the small
insect carefully with forceps and mount it by touching it on its thorax (right side) to
the drop of glue. Adjust the insect so that it remains squarely in position, and then
allow the glue to dry.
Pinning and Spreading Butterflies and Moths
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Page 41
When pinning and spreading a butterfly or moth, before you begin to work, cut
several thin strips of paper about 1/4" wide and 8"-10" long. Once these are ready,
pick up the insect by the thorax and carefully push a pin through the middle of the
thorax. Adjust the position of the butterfly on the pin and make sure that it is level,
both on the sides and in both front and back. Adjust the width of the groove in the
spreading board to be just slightly wider than the body of the butterfly. Push the pin
into the slot of your spreading board until the bases of the wings are just level with the
top of the two side pieces.
Slip a paper strip between the wings (if they are upright) and use it to force the
wings on one side down into position. Pin the ends of the paper down to hold the
wings loosely in place. Do the same with the wings on the other side, also pinning the
ends of the paper down.
Now take another insect pin or needle and slip the point through the leading
edge of the right forewing (there is a strong vein just at the front edge of each wing)
near its attachment to the thorax. Be careful not to tear the wing. Loosen the forward
end of the paper strip and gradually bring the forewing up into final position. Pin the
wing down with a paper strip. Repeat this procedure with the forewing on the other
side. Using the same technique, bring both hindwings into proper position and fasten
all four wings firmly with the paper strips.
Note carefully that the rear edge of the two forewings should make a perfectly
straight line across the back. The hindwings should be pinned so that the rear edge is
held just slightly away from the abdomen. Position antennae with pins and if the
abdomen has drooped, prop it up with pins so that it dries in a natural position. Allow
specimens to dry for several days before you remove the pins.
Labeling Insects
A collection has little value unless each insect is properly and accurately
labeled. Labeling must be done as soon as possible after collecting, pinning and
mounting or vital information may be lost. Their precise collection locations,
habitats, and data on plants on which they were found are important documentation.
The top label should have the place from where the insect was collected, the
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collection date and the name of the collector (Fig. 19). The lower label should show
the Order name of the insect. Many entomologists place another label beneath the
collection label which gives the host plant, habitat or other pertinent information.
Fig. 19 Essential information on an insect label
REFERENCE:
1: Pedigo, Larry. P. (2002). Entomology and pest management. (4th ed.). Printice Hall
of India. New-Delhi.
2: Robinson, D.H. (2001). Entomology principles and practices. Agrobios (India).
Jodhpur.
3: University of Sydney. (2004). Importance of entomology. Retrieved July 21, 2008,
from http://bugs.bio.usyd.edu.au/Entomology/importance/importance.html
4. Keith, David L. and Heng-Moss, Tiffany. (n.d.). Collecting insects. Retrieved July
17, 2008, from http://entomology.unl.edu/tmh/ent115/labs/collecting.htm
5. Insect external morphology. (n.d.). Retrieved June 11, 2008, from
http://basicentomology.ifas.ufl.edu/lab5
6. Meyer JR (2009). General Entomology. North Carolina State University. Retrieved
on Septeber 1, 2009, from
http://www.cals.ncsu.edu/course/ent425/library/tutorials/index.html
7. K-State Research and Extension, 4-H Entomology , Electronic Document
PINNING AND LABELING INSECTS FOR KANSAS 4- H ENTOMOLOGY COLLECTIONS
http://ag.udel.edu/extension/4h/projects/pdf/insectpinning.pdf
http://bugs.bio.usyd.edu.au/learning/resources/Entomology/introduction.html
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