34 



ECONOMIC ENTOMOLOGY 



The cruciform type prevails among the holometabola. The body 

 is cyHndrical, and the legs, antennae and cerci are much reduced. 



Many transitional forms, however, occur, and it is believed that 

 the cruciform type has been developed from the thysanuriform. 



Ecdysis or Moulting.— AW larvae shed their outer skin (cuticula), 

 at intervals to allow for growth. The number of moults varies in 

 different insects, but is constant for the same species under the same 

 conditions. 



In the Lepidoptera the larva is known as a caterpillar, and is char- 

 acterized by the possession of three pairs of true legs, and usually 



Pig. 38. — Types of larvae, a. Grub of asparagus beetle; b, cutworm; c, cabbage 

 root maggot; d, fall canker worm;'e, maggot of honey bee; /, spring canker worm; 

 g, false caterpillar of saw fly; h — a, b, c, nymphs of locust; i — a, b, c, d, e, nymphs of 

 squash bug. {After various authors.) 



five pairs of prolegs on the abdominal segments. In the Diptera and 

 Hymenoptera the larva is a maggot, characterized by the absence of 

 legs. In the group of Saw-flies of the Hymenoptera, however, the 

 larvae are caterpillar-like, possessing three pairs of true legs and often 

 seven or more pairs of prolegs. 



In the Coleoptera the larva is termed a gruh, and has usually but 

 three pairs of legs (Fig. 38). 



Classification of Larvae. — Escherich classifies larva; as follows: 

 Primary Larva. — Larva; like the adult, and without provisional larval organs 

 — Thysanura, Mallophaga, PedicuUda, Orthoptera, Isoptera, Corrodcntia. 



