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Introduction to Insects: Structure, Function, Development and Feeding Behavior. Thomas J. Weissling Assistant Professor of Entomology University of Florida Fort Lauderdale Research. THE INSECTS. Fossil records indicate insects on land more than 300 million years ago - mid paleozoic.

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Introduction to Insects: Structure, Function, Development and Feeding Behavior

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


4) A chitinous exoskeleton, which is periodically shed and renewed

as the animal grows

University of Nebraska-Lincoln, Department of Entomology, Leon Higley


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


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%)


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.


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 regulator)
      • 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 arthropods).
      • 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

Photos: 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