Patterns of nymphal development in the desert locust, Schistocerca gregaria, with special reference to phase-dependent growth and extra molting

Abstract

Extra molting is typically observed in solitarious forms in the desert locust, Schistocerca gregaria. The present study examined the relationships between nymphal development, extra molting and adult body size in this locust by rearing solitarious hatchlings (obtained from isolated-reared locusts) under isolated conditions. Nymphs passed either five or six nymphal stadia and grew at nearly constant rates during all stadia, except for the 2nd and 3rd nymphal stadia in the group with extra molting. Development during the 2nd stadium appeared to have influenced whether the nymphs underwent extra molting, and once reaching the 3rd stadium, their development proceeded at a constant rate depending upon the body weight in this stadium. Nymphs which were relatively small at hatching had smaller body sizes during the nymphal stadia than those which were relatively large at hatching, and tended to undergo extra molting. Nymphs became larger if they underwent extra molting, but in the group with the same number of nymphal molts they tended to attain smaller adult body sizes as nymphal development was prolonged. These results suggested that phase-related nymphal development was influenced not only by body size at hatching but also by nymphal growth during the 2nd stadium.