Archive:Loosestrife/Basic Insect Biology

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Wilson, L.M.; Schwarzlaender, M.; Blossey, B.; Randall, C.B. Biology and Biological Control of Purple Loosestrife. United States Department of Agriculture, Forest Service. Forest Health Technology Enterprise Team. FHTET-2004-12. 78 p.

Insects are a very large, diverse class of animals. Basic knowledge of insect anatomy and lifecycle will help in understanding insects, and recognizing them in the field.

Adult insects have several unique characteristics; an exoskeleton (outside skeleton), a segmented body comprised of a head, thorax, and abdomen, and three pairs of legs (Figure 6). Because insects have a skeleton on the outside, they must shed their skeleton as larvae in order to grow. This process of shedding the exoskeleton is called molting.

Figure 6. Diagram of beetle anatomy (a ladybird beetle is used as the example).

The period between molts is called an instar. As larvae, insects grow a lot, often having to go through three to five molts.

Mature larvae molt into a pupa, the stage when the insect body changes from a larva into the adult. Insect development from an egg to adult is called metamorphosis. The insects we will be discussing in this manual go through complete metamorphosis, meaning they have four developmental stages: egg, larva, pupa, and adult (Figure 7). Once the insects become adults, they stop growing, and therefore stop molting.

Figure 7. Insect lifecycle showing complete metamorphosis (a weevil is used as the example).