Introduction to the Studyof Insects

for Master Gardeners

Richard Sprenkel

University of Florida/IFAS

North Florida Research and Education Center

Phylum Arthropoda

An arthropod is an animal that is distinguished from other animals in having an external skeleton and jointed appendages.

Arthropods

Examples of arthropods include insects, ticks, spiders, horseshoe crabs, millipedes, chiggers, centipedes, shrimp, sowbugs and scorpions.

Class Insecta An insect is an arthropod having three body

regions (head, thorax and abdomen), three pair of legs, one pair of antennae and generally one or two pair of wings in the adult stage. Head with antennae, eyes and mouth. Three segmented thorax with legs and wings (if

present). Abdomen composed of varying number of

segments depending on the species. Internally contains most of the digestive system and the reproductive system.

Insects

• Old Group– Oldest fossils are 400 million years old.

• Diverse– 80% of all described animal species are insects.

One-half of the described species of insects are beetles.

• Numerous– It has been estimated that the total weight of all

insects on the planet exceed the combined weight of all people on earth by a factor of 200 times.

Old Group

Homo sapiens 0.3 Mil Yr

Dinosaurs 135 (65 - 250) Mil Yr

Flowering Plant 135 Mil Yr

Birds 180 Mil Yr

Mammals 225 Mil Yr

Modern Insect Orders 270 Mil Yr

Winged Insects 350 Mil Yr

First “Insect” 400 Mil Yr

Insect as Pests

Usually an insect is considered to be a pest if it transmits diseases (mosquitoes), feeds on food (flour moth), crops (corn earworm) or structures (termite) or is a nuisance (cockroaches and lovebugs).

World-wide only 8% of insects are considered pests. In the U.S., only 600 of the100,000 described species (0.6%) are pests.

Beneficial Insects

• Pollinators (apples, watermelons, squash)

• Products (honey, silk, dyes)

• Scavengers

• Predators/parasites

• Food for fish and birds

• Scientific study

• Art, religion, relaxation

Some of the ‘Systems’ Which make Insects Unique

• Digestive System

• Circulatory System

• Nervous System

• Respiratory System

Digestive System

The digestive system is basically a tube that runs through the middle of the body. It consists of a foregut, midgut (stomach) and hindgut.

The excretory system is made up of malpighian tubules (which function similar to our kidneys) which remove wastes from the insect body through the hindgut.

Circulatory System

The circulatory system is an open system that is not confined to arteries and veins. Haemolymph (insect blood) is circulated through the body cavity by a dorsal “heart” and a short aorta. The blood is picked up in the abdomen and carried forward to the head where to flows back into the body cavity.

Nervous System

The nervous system consists of a small brain in the head that is connected by a double nerve cord to a series of ventral ganglia or nerve centers located in several segments of the body.

Respiratory System

Insects do not have lungs. They breathe passively (diffusion of oxygen in and carbon dioxide out) through a system of tubes called tracheae. The tracheae open to the outside through spiracles.

Inside the body, the tracheae branch into finer tubes called tracheoles which provide oxygen to cells.

The Class Insecta (Hexapoda)is divided into Orders

The 30-35 Orders of Insectsare Separated on the Basis of:• Wings

– Structure, number, etc.

• Mouthparts– Chewing– Piercing-sucking (mosquitoes, bugs, etc.)– Siphoning (butterflies, moths)

• Metamorphosis– Simple (or Incomplete)– Complete

Simple Metamorphosis

• Also called incomplete metamorphosis.

• Egg > nymph > adult

• Aphids, grasshoppers, cockroaches, true bugs

Complete Metamorphosis

• Egg > larva > pupa > adult

• Moths, butterflies, beetles and flies

Insect Orders ContainingPlant Pests of

Economic Importance• Orthoptera (grasshoppers and crickets)

• Hemiptera (true bugs, aphids and leafhoppers)

• Thysanoptera (thrips)

• Coleoptera (beetles)

• Diptera (flies and mosquitoes)

• Lepidoptera (butterflies and moths)

Orthoptera (grasshoppers)

• ortho, straight; ptera, wings

• Characteristics– Front wings are elongated with many

veins. Hind wings have many veins and are folded fanwise beneath the front wings.

– Chewing mouthparts– Simple metamorphosis

Hemiptera (true bugs, aphids and leafhoppers)

• hemi, half; ptera, wings• Characteristics

– In many species in this Order, the basal portion of front wing is thickened and leathery while apical portion is membranous. At rest, wings are held flat over body with membranous tips overlapping (e.g. stink bug).

– Piercing-sucking mouthparts– Simple metamorphosis

Thysanoptera (thrips)

• thysano, fringe; ptera, wings

• Characteristics– The two pair of wings are stout and fringed

with long hairs.– Sucking mouthparts– Complete metamorphosis

Coleoptera (beetles)

• coleo, sheath; ptera, wings

• Characteristics– In most species the front pair of wings is

thickened and hard. The hind wings are membranous.

– Chewing mouthparts; mandibles are usually well developed

– Complete metamorphosis

Diptera (flies)

• di, two; ptera, wings• Characteristics

– One pair of wing; hind wings are reduced to small knobbed structures called halteres.

– Sucking type of mouthparts in adults but with considerable variation; mouthparts in larvae of the primitive families are of the chewing type and the mandibles move laterally, in the larvae in the higher families mouthparts are reduced and move in a vertical plane.

– Complete metamorphosis

Lepidoptera (butterflies)

• lepido, scale; ptera, wings

• Characteristics– Most readily recognized by scales on

wings, body and legs.– Sucking mouthparts - adult; chewing

mouthparts- immature stage– Complete metamorphosis

Insect Management

• Genetic– Resistant varieties

• Biological– Conservation and augmentation

• Cultural, Mechanical– Crop rotation, destruction of residue, hand

picking, etc.

• Chemical

Chemical Control• Should be used as a last resort

– Treatment based on scouting and/or anticipated loss or damage.

• A few of the classes of insecticide chemistry– Cholinesterase inhibitors (Diazinon, Dursban,

Malathion, Orthene, Sevin)– GABA blockers (pyrethrins, pyrethroids)– Neonictinoid disrupter (imidacloprid)– Biological (Bacillus thuringiensis)– Insect growth regulators (Amdro)– Soaps and oils

Some Active Ingredients Labeled for Homeowner Use

• Acephate • Bacillus

thuringiensis • Bifenthrin + fertilizer• Carbaryl • Cyfluthrin • Esfenvalerate

• Horticultural oils• Imidacloprid• Malathion • Permethrin • Soaps• Trichlorfon

Richard SprenkelUniversity of Florida/IFAS

North Florida Research and Education Center, QuincyCopyright 2004, University of Florida

Pre-Test/Post-Test

A. Taxonomically, insects are separated from the other arthropods by the fact that the insects have1. Fewer legs2. Three pair of legs, three body regions and wings3. Segmented appendages and an exoskeleton4. More complex life cycles5. Don’t know

B. According to the fossil record, insects are 1. Approximately 265 million years old2. Nearly as old as the oldest known dinosaur3. Slightly older than the oldest dinosaur4. More than 100 million years older than the oldest known dinosaur5. Don’t know

Pre-Test/Post-Test

C. Taxonomists have1. Divided the insects into 12 Orders2. Separated the Orders based on type of mouthparts, type of wings and

coloration in the adult stage3. Separated the Orders based on type of legs, type of wings and type of

development4. Separated the Orders based on type of wings, type of mouthparts and type

of development5. Don’t know

D. In the United States1. Approximately one-half of the described species of insects are considered

to be pests2. Slightly less than 25% of the described species of insects are considered to

be pests3. Less than 1% of the described species of insects are considered to be pests4. There are about equal numbers of pest and beneficial species of insects5. Don’t know

Pre-Test/Post-Test

E. Tracheoles are1. Part of the insect digestive system2. Part of the insect respiratory system3. Part of the insect nervous system4. The ‘foot pad’ of the insect5. Don’t know

F. Insects with complete metamorphosis have1. Two developmental stages2. Three developmental stages3. Four Developmental stages4. Five developmental stages5. Don’t know

Pre-Test/Post-Test

G. In the insect circulatory system1. Haemolymph is pumped from the rear of the insect toward the head2. Haemolymph is pumped from the head toward the rear of the insect3. Haemolymph is pumped from the heart both toward the head and

rear of the insect in a closed system4. There is no means for pumping the haemolymph5. Don’t know

H. In insect management, augmentation and conservation are components of 1. Cultural control2. Genetic control3. Biological control4. Chemical control5. Don’t know