Class Insecta: The Insects

Entomology

About 1,000,000 different known (described) species of insects in the world, and some experts estimate that there might be as many as 30,000,000. Make up 75% of all animal species.

About 32 orders (depending on whose taxonomic system you use) of which the largest is the beetles (Coleoptera) with 125 families and around 500,000 species.

Range in length from 0.25 mm (a beetle) to 36 cm (a walking stick).

Inhabit all habitats, though most terrrestrial. Many in freshwater, burrow in logs or soil, in leaf litter, burrow inside leaves, live on snow, some parasitic (external or internal), even a few marine species. May be herbivores, carnivores, omnivores, scavengers, parasites. Important in decompositon, pollination, making of honey and silk.

Less than 1% of all insect species are pests (only a few hundred serious ones). Many of these are in the Order Diptera, the flies, mosquitoes, and midges.

Social insects - ants, bees, wasps, termites. Very organized with social castes.

External features - Fig 33.33

- exoskeleton containing chitin - requires molting for growth - Fig 49.30

- Have three body segments: head, thorax, abdomen

- Have three pairs of legs, all attached to thorax

- Have one pair of antennae - Have chemoreceptors - Fig 49.5b

- May have one or two pairs of wings - Fig 33.32

- Most possess compound eyes - Fig 49.8a - Fig 49.8b - Vision

- Elaborate mouthparts, widely variable

Internal features - Fig 33.33

• Open circulatory system - Fig 42.2
• Respire via trachea with spiracles - Fig 42.22
• Malpighian tubules - Fig 33.33
• Separate sexes - Fig 46.7 - Image -Some insects with parthenogenesis

Life histories and representative orders - See Table 33.6 - Types of metamorphosis

- Immature insects undergo regular molting, stages called instars. Adult insects never molt.

 

- Incomplete metamorphosis - egg > nymph (or larva) > adult

1) Wings develop during juvenile stages in external pads

2) Immature stages generally called nymphs

 

Examples:

1) Odonata - dragonflies and damselflies- chewing mouthparts

2) Orthoptera - grasshoppers and crickets- chewing mouthparts

3) Blattodea - cockroaches - chewing mouthparts

4) Isoptera - termites - chewing mouthparts

5) Anoplura - sucking lice - piercing-sucking mouthparts

6) Hemiptera - true bugs - piercing-sucking mouthparts - many plant pests

7) Homoptera - leafhoppers, treehoppers, cicadas, aphids - piercing-sucking mouthparts - many plant pests

 

- Complete metamorphosis - Fig 45.2

1) Egg > larva > pupa > adult - Fig 33.34 See a butterfly emerging!

2) During pupal stage, wings appear.

 

Examples:

1) Lepidoptera - moths, butterflies - coiled proboscis

2) Diptera - flies, mosquitos - piercing-sucking mouthparts

3) Siphonaptera - fleas - piercing-sucking mouthparts

4) Coleoptera - beetles - chewing mouthparts - Image

5) Hymenoptera - bees, wasps, ants - chewing mouthparts

Some example images: damselfly, water strider (Hemiptera), and beetle and: moth, mosquito and wasp