Larva

Frederick W. Stehr

Michigan State University

The term "larva" is currently used for all immatures that are not eggs, pupae, or adults. When larva is used in this comprehensive sense, the subcategories include exopterygote larva (for Hemimetabola, which have the wingpads developing externally) and endopterygote larva (for Holometabola, which have the wings developing internally as histoblasts in the larva, becoming external wingpads in the pupal stage).

Larvae occur in a great diversity of sizes, shapes, and colors. Colorful ones almost always live in exposed habitats where their colors and shapes offer cryptic concealment or where their bright colors and spines warn potential predators that they are not to be eaten. Larvae that live in concealed habitats are nearly always combinations of white, gray, black, or brown.

Instar has been conventionally defined as the stage the larva is in between molts. Stadium is defined as the interval of time l\ i/l >■ V7 v

L = 20 mm

FIGURE 1 A campodeiform ground beetle larva, Harpalus (Carabidae). (Reproduced from A. Peterson, 1951, Larvae of Insects, Vol. 2, with permission of Jon A. Peterson.)

between molts. Others contend that the instar is properly defined as the stage the larva is in between apolysis (separation of the old cuticle) and the molt to the next stage, and a pharate (next-stage) larva would be present before the next molt.

There are some general terms used for types of holometa-bolous larvae that have broad usage. Campodeiform larvae (Fig. 1) are somewhat flattened and have an elongate body, thoracic legs that are well developed, a head that is directed forward, no abdominal prolegs, and antennae and cerci that are usually conspicuous. This larval type is common in the Coleoptera (beetles), Megaloptera (dobsonflies and fishflies), Neuroptera (lacewings and antlions), and Raphidioptera (snakeflies).

Elateriform larvae (Fig. 2A) are somewhat similar to campodeiform larvae, but their body is more elongate, subcylin-drical, and more heavily sclerotized. This type is common in the Elateridae (click beetles) and other Coleoptera.

Scarabaeiform larvae (Fig. 3) have a C-shaped, whitish body, a dark head, and well-developed thoracic legs. White grubs (Coleoptera: Scarabaeidae) are the best example.

Eruciform larvae are caterpillar-like and have a cylindrical body and well-developed thoracic legs, and prolegs are present. This type is common in the Lepidoptera (butterflies and moths), Mecoptera (scorpionflies), and Hymenoptera (sawflies only).

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