Download The Thorax.

Introduction to Insects:
Structure, Function,
Development and Feeding
Behavior
THE INSECTS
•Fossil records indicate insects on land more than 300
million years ago - mid paleozoic
Insects are from an ancient lineage that included trilobites and
crustaceans which were abundant in the oceans over 500 million
years ago. Trilobites are extinct:
but we are surrounded by crustaceans…most of which are aquatic.
Insects shared the terrestrial habitat with various relatives such
as spiders, ticks, mites, and scorpions.
Insects are in the phylum Arthropoda. This group contains
animals that share the following characteristics:
1) Body segmented, the segments usually grouped in two or three
rather distinct regions
2) Paired segmented appendages (from which the phylum
gets its name)
3) Bilateral symmetry
4) A chitinous exoskeleton, which is periodically shed
and renewed as the animal grows
University of Nebraska-Lincoln, Department of Entomology, Leon Higley
5) A tubular alimentary canal, with mouth and anus
6) An open circulatory system, the only blood vessel
usually being a tubular structure dorsal to the
alimentary canal with lateral openings in the
abdominal region
7) The body cavity a blood
cavity or hemocoel, the
coelom reduced
8) The nervous system consisting of an anterior
ganglion or brain located above the alimentary
canal, a pair of connectives extending from the brain
around the alimentary canal, and paired
ganglionated nerve cords located below the
alimentary canal
9) The skeletal muscles striated
10) Excretion usually by means of tubes (the
Malpighian tubules) that empty into the
alimentary canal, the excreted materials
passing to the outside by way of the anus
11) Respiration by means of gills, or tracheae
and spiracles
12) The sexes nearly always separate
The arthropoda is divided into 4 smaller groups called
classes:
Crustacea
Myriapoda
Arachnida (Chelicerata)
Insecta (Uniramia)
The Arachnida (Chelicerata) have no antennae and the
mouthparts are chelicerae which are not like the mouthparts
of insects. They are an 8-legged group in an evolutionary
line that diverged from the insects in the mid-paleozoic
The Myriapoda (centipedes, millipedes, etc.) have
antennae, mandibles, maxillae and tracheal system
but have only two body regions, and they add
segments as they molt (anamorphosis)
At least ½ of the animals currently
occupying the earth are insects
(approximately 1.5 million different
species)
Of all insect species in the world
Less than 1%
Considered
to be pests
Beneficial or not
considered to be pests
(> 99%)
 Eat about anything imaginable, occupy about every
imaginable niche
Why are insects
so successful?
• Have wings…dispersive
 Diverse mouthparts
Relation of insects to humans:
1. Beneficial:
(Pollination, Honey, Beeswax, silk [65-75 million pounds
produced annually], shellac, dyes, break down raw
materials, aerate soil, biocontrol of weeds and bad bugs,
human food, medicine & surgery [cantharidin, bee
venom for arthritis, blow fly larvae], research animal
2. Aesthetic Value:
3. Injurious: plants, stored foods, woods, fabrics, humans
and animals
Proper identification is
essential in pest
management
The Insects
1. Three, usually distinct body regions (head,
thorax, and abdomen)
2. One pair of segmented antennae
3. Usually have one pair of compound eyes
4. Three pair of segmented legs, one pair on each
of the three thoracic segments
5. Usually with two pair of wings, some have only
one pair (i.e., flies) or no wings at all.
The Head. The insect head serves a number of functions, such
as feeding and sensory perception.
The Thorax. The thorax is primarily responsible for locomotion.
Made up of 3 segments, the prothorax, mesothorax, and
metathorax. A pair of legs arise from each segment. Wings,
if present, arise from meso-, and meta-thorax.
The Abdomen is responsible for excretion, and reproduction.
Metamorphosis. The process of change from egg to adult.
Incomplete or gradual metamorphosis. The immatures, or
“nymphs” look similar to the adults (grasshoppers, aphids,
cockroaches).
Complete metamorphosis. The immatures, or larvae look
nothing like the adult. The larvae pass through a pupal stage
to change into the adult form (wasps, beetles, moths,
butterflies, flies).
Feeding
 Plant-feeders, blood-feeders, parasites, scavengers…to
name a few
Types of Injury Insects Cause to Plants
1. Stand Reducers (i.e. cutworms): produce an immediate
loss in plant biomass resulting in decreased photosynthesis.
Effects are governed by pest number, and timing of
damage
2. Leaf-Mass Consumers (i.e. grasshoppers): Leaf
consumption is generally thought to directly affect absolute
photosynthesis of the canopy.
3. Assimilate Sappers (i.e. Aphids): Insects generally with
piercing/sucking or rasping mouthparts. Tend to remove plant
carbohydrates and nutrients after carbon is taken up but before
it is converted to tissue.
4. Turgor Reducers (i.e. Citrus root weevil larvae): Are
generally root and stem feeders that affect plants water and
nutrient balance. Severe reductions in water uptake results in
decreased turgor which decreases the expansion of new leaves,
stems and fruit. In addition, photosynthesis can be decreased.
5. Fruit Feeders (i.e. Codling moth): feeding on fruits
usually results in direct destruction of harvestable produce
which affects quality, yield or both.
6. Architectural Modifiers (i.e. lodging, corn rootworm
larvae): Results in morphological changes in plant architecture.
Can result in reduction of physiological as well as harvestable
yield.
Also gall forming insects.