GENERAL ZOOLOGY 

 Adult 



Fig. 15.21. 



Life cvcle of an ametabolous insect. 



Juvenile 

 stages 



Embryo 



temperate climates most species of locusts lay their eggs during late summer 

 and autumn. The eggs undergo a period of dormancy, or diapapse, and re- 

 sume development only after they have been subjected to low temperature. 

 Thus, the young do not normally hatch until the following spring. At hatch- 

 ing, the young locust, or nymph, resembles the adult, although the head is 

 relatively larger and the wings are very small (Fig. 15.20). The final size and 

 normal adult proportions are reached through a series of molts. 



Insect Life Cycles and Metamorphosis. The life cycles characteristic 

 of different insects range from very simple to extremely complex. Insects that 

 on other evidence are considered among the most primitive in existence show 

 what is probably the ancestral type of development. Eggs hatch to produce 

 young which are exactly like the adults, except that they are smaller and 

 are incapable of sexual reproduction. Increase in size and development of 

 sexual maturity occur during a series of successive molts. Such a simple life 

 cycle, which does not include metamorphosis (change of form), is spoken of as 

 ametabolous (Fig. 15.21). 



A diflferent type of life cycle is characteristic of many insects such as locusts, 

 which are not so primitive but are of rather generalized form. The young 

 emerging from the eggshell is like a miniature adult in most respects, but its 

 proportions are diflferent, and the wings are relatively undeveloped. This 

 immature individual is termed a nymph, which, like the young locust, gradually 

 develops wings and attains adult proportions through a series of molts. This 



Adult 



Fig. 15.22. Life cycle of a paurometabolous in.sect. 



Nymphal 

 stages 



Embryo 



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