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Introduction to Insects:
Structure, Function,
Development and Feeding
Thomas J. Weissling
Assistant Professor of Entomology
University of Florida
Fort Lauderdale Research
•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
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
10+ legs, 2 body regions, mandibles, 2 pairs of antennae, no wings
1-2 pair of legs per segment, 2 body regions, mandibles, 1 pair of antennae, no wings
Arachnida (Chelicerata)
8 legs, 2 body regions, chelicerae, no antennae, no wings
6 legs, 3 body regions, mandibles, 1 pair of antennae, 0, 2, or 4 wings
The Arachnida (Chelicerata) have no antennae and the mouthparts
are chelicerae which are not homologous to 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)
In the early myriapod lineage, certain groups appeared in which
segments and legs were not added at molting (epimorphic).
Legs were retained on the three segments behind the head, and the
remainder of the body included only 11 segments
When the three segments with legs became capable of moving
the creature, the rest of the body became more specialized (for
reproduction, viseral functions, etc.)
Ended up with three body regions.
At least ½ of the animals currently
occupying the earth are insects
(approximately 1.5 million different
Of all insect species in the world
Less than 1%
to be pests
Beneficial or not
considered to be pests
(> 99%)
 Eat about anything imaginable, occupy about every imaginable
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 (Spanish fly-blister beetle),
bee venom for arthritis, blow fly larvae (maggot therapy)],
research animal
2. Aesthetic Value: jewelry, pets, nice to look at
3. Injurious: plants, stored foods, woods, fabrics,
humans and animals
Proper identification is
essential in pest
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,
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).
Molting (and control of molting)…IGR’s (Insect Growth
Diapause/Estivation (slowing of activity)
Reproduction: sexually, parthenogenetically (A form of
reproduction in which an unfertilized egg develops into a new
individual, occurring commonly among insects and certain other
Mating (mate finding)
Oviposition-process of laying eggs (fertility vs. fecundity –
the ability to reproduce)
 Plant-feeders, blood-feeders, parasites, scavengers…to name a
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. Yield losses are not always proportional
to the damage.
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.
Author: Tom Weissling, University of Florida
University of Florida
University of Nebraska
University of California
Entomology And Nematology Department
Copyright University of Florida 2000
For more detailed information see the Featured
Creatures WWW site at