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Insects
(Phylum Arthropoda; Sub-Phylum Uniramia)
Evolved over 300 million years ago
Most successful group of animals (700,000 to 10
million species)
Diversity (species and
variety)
Numbers (population
size)
Success due in part to
enormous range of
variation
Structural
(morphological)
Physiological
(chemical)
Behavioral
Characteristics and Classification
Body - 3 parts
Head with 1 pair of
antennae
Thorax with 3 pair of
jointed legs and in many
species 1-2 pair of wings
Abdomen with 11
segments (lacks wings
and legs)
Success of the
Found virtually everywhere except the deep ocean
Extremely short life span -> rapid adaptation to new
environments
Small size -> greater partitioning of habitats while
minimizing competition
Flight -> greater dispersal, escape from predation, and
movement into environments less accessible to other
species
Insects and Human Society
Positive impact
Major pollinator of flowering
plants (2/3 of all plants)
Food for fish, birds and mammals
(important link in food web)
Help recycle materials (termites)
Useful biproducts (honey and silk)
Negative impact
Agricultural pests
Spread disease
Grasshoppers
3 main body segments
Head (brain and sense
organs)
Antennae
Compound and simple eyes
Complex moth parts
Thorax (legs and wings attached)
Prothorax and mesothorax (each have pair of walking
legs)
Metathorax (jumping legs
Abdomen (organs
of reproduction,
digestion,
respiration, and
excretion)
2 pair of wings
Leathery
protective forewing
(mesothorax)
Hind wing which
is used for flight
(metathorax)
Digestive System
Specialized mouthparts
(liplike labium and labrum,
jawlike mandibles and
maxillae)
Salivary glands (produce
saliva)
Digestive ceca (produces
digestive enzymes)
Food -> mouth -> esophagus -> crop (storage) ->
gizzard (chitinous plates shred it) -> stomach (mid gut)
(mixes with gastric enzymes from ceca and absorbed) > hind gut (colon and rectum) -> anus
Excretory System
Malpighian tubules in hindgut remove wastes from
blood and deposit them in the rectum
Circulatory System
Open circulatory
system
Blood -> aorta ->
hearts (muscular
region of aorta in
posterior abdomen) ->
anterior coelom (head)
-> abdomen (absorbs
and disperses
nutrients) -> aorta via
ostia
Respiratory System
Air -> spiracles
(opening in
thorax and
abdomen) ->
tracheae
(network of air
tubes) -> body
tissues
Contraction of
abdomen
reverses process
Nervous System
Simple brain
Ventral nerve cord
3 simple eyes (detect
light)
2 compound eyes
(composed of
hexagonal lenses
capable of detecting
movement but not
sharp images)
Tympanum (detects
sounds; located on first
abdominal segment)
Antennae (detects touch
and smell)
Reproductive System
Sperm deposited into
female's seminal
receptacle (stored until
eggs are released)
Eggs fertilized
internally
Ovipositor (pair of
pointed organs at tip of
abdomen) used to dig a
hole in soil and deposit
eggs
Development
Metamorphosis - developmental
changes -> distinct changes in form
and size
Incomplete Metamorphosis
3 stages (egg, nymph, and adult)
Nymph- smaller immature form;
similar to adult but underdeveloped
reproductive organs and lack wings
Examples are grasshoppers and
termites
Complete Metamorphosis
4 stages (egg, larva, pupa, and adult)
Examples are butterflies, beetles and most other
insects
Hormonal Control
Controlled by sequential expression of genes
Interaction of 3 hormones (brain, molting and
juvenile)
Brain hormone stimulates
release of molting hormone
(effect depends on level of
juvenile hormone)
Juvenile hormone level high
-> molting hormone -> larva
molts
Juvenile hormone level
decreases -> molting
hormone -> larva develop
into pupa
Juvenile hormone absent ->
molting hormone -> pupa
develops into adult
Importance of Metamorphism
Different developmental
stages -> different
functions
(specializations)
Eliminates energy
conflicts between growth
and reproduction
Eliminates competition
between life stages
Multistage life cycle
helps survive harsh
weather
Defense
Defensive adaptations (agressive
and passive) -> enhanced survival
Camouflage (cryptic coloration)
Warning coloration
Mullerian mimicry- poisonous or
dangerous species having similar
patterns of coloration
Batesian mimicrynonpoisonous or
nondangerous species
having similar pattern or
color to a poisonous or
dangerous unrelated
species
Insect Behavior
Social behavior in
honeybees
Behaviors are genetically
determined (instinctual or
innate)
Division of labor ->complex
societies -> interdependence
and need for communication
Hive consists of 3 distinct
forms
Workers - sterile females;
majority of individuals in
hive
Queen - fertile female; only
function is reproduction
Drones - male bees; only
function is
Workers
Average life span approximately 6
weeks
Perform many functions at
different times during their lives
1st stage - feed honey and pollen
to queen, drones and larvae (nurse
bees); secrete royal jelly (high
protein diet)
2nd stage - Stop producing royal
jelly and begin secreting wax ->
build and repair hive, guard hive
and fan wings to circulate fresh air
in hive
3rd stage - gather nector and pollen; legs modified with
special structures to collect pollen; ovipositor modified
for defense (stinger)
Queen and Drones
Queen identical to workers
except continuously supplied
with royal jelly; Queen secretes
"queen factor" which prevents
other female larvae from
becoming sexually mature
Mates only once; sperm stored
in seminal receptacle for up to 5
years or more
Drones (haploid (n) males)
develop from unfertilized eggs;
sole function to deliver sperm to
queen; must be feed by workers
Communication
Pheromones - chemicals released by an animal that
affects the behavior or development of other animals of
the same species
Sounds
Tapping, rubbing, or signaling
Honey Bee communication
Round dance - food source
near but no indication of
exact location
Waggle dance- food far
from hive, dirction of food
indicated by the angle of the
straight run and the distance
indicated by the duration
and the number of waggles