PHYSIOLOGY AND BEHAVIOR OF THE ARTHROPODA ^$\ 



Figure 17.5. Effect of the removal of the corpora allata in the silkworm. Moth at 

 left is normal. Moth at the right developed from a young caterpillar whose corpora allata 

 were removed. It pupated at the next molt after the operation. (After Bodenstein from 

 Fukuda.) 



He implanted corpora allata from small nymphs into the hemocoel of 

 large nymphs that ordinarily would mature on the next molt. The result 

 was another nymphal stage the size of an adult (Fig. 17.6). These nymphs 

 eventually molted again to produce oversized adults. 



Further interactions among the endocrine organs are evident in the 

 control of diapause in moths. Diapause is a state of arrested develop- 

 ment which occurs in many eggs, insect pupae and plant seeds. The large 

 moth, Platysamia cecropia (Fig. 16.24), overwinters as a pupa formed in 

 the middle or late summer. If newly formed pupae are kept at 75° F. 

 they remain inactive for five or six months. Eventually, however, de- 

 velopment does proceed and the moths emerge four weeks later. If new 

 pupae are chilled to 40° for six weeks and subsequently placed at 75°, 

 development proceeds at once. Hence, chilling leads to an end of 

 diapause and shortens the period of pupal life. Carroll Williams, finding 

 that if a chilled and an unchilled pupa are grafted together (Fig. 17.7) 

 both will develop, suggested that diapause is under hormonal control. He 

 found also that the brain of a chilled pupa implanted in an unchilled 



Figure 17.6. The effect of adding corpora allata in Rhodnius. The last stage nymph 

 (left) normally molts to form an adult (center). When corpora allata from young nymphs 

 are added to a last stage nymph, it molts to form an oversized nymph (right). This later 

 molts again to become an oversized adult. (After Wigglesworth.) 



