Phase polymorphism in Schistocerca gregaria: Reproductive parameters

Solitarious phase Schistocerca gregaria were selected according to the criterion of the occurrence of an extra stadium during larval development. The proportion of locusts undergoing an extra ecdysis increased within one generation of rearing under isolated conditions but it failed to reach 100% throughout an observation period encompassing six generations. A higher proportion of female locusts exhibited an extra stadium indicating sexual dimorphism in this phase character.The number of eggs per pod produced by solitarious females was larger than their gregarious counterparts. This was shown to be due to an increase in the number of ovarioles and a relative decrease in the proportion of non-functional oöcytes in solitary females, confirming earlier work.The inverse relationship between ovariole numbers and oöcyte size characterizing locust phase polymorphism was examined. Vitellin content of ovaries containing mature oöcytes was similar in gregarious and solitarious females. However, vitellin content per oöcyte was less in the latter suggesting that the increase in ovariole number may occur at the expense of oöcyte size and vitellin content.