Increased juvenile hormone synthesis and decreased fertility in aging Schistocerca gregaria

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Abstract
The fertility of aging Schistocerca gregaria females of both solitary and gregarious phases is markedly reduced in comparison with that of young females. Examination of eggs (from both young and aging females) maintained in vitro revealed that the decreased fertility of aging females of both phases could be attributed to a decrease in viability of eggs. This, in turn, was found to be in large part due to an increase in the proportion of embryos showing inhibited development. The proportion of inhibited embryos, in pods from young and old females, respectively, increased from 5 to 42% for gregarious animals and from 3 to 38% for solitary animals. Inhibition was found to occur at all stages from blastokinesis to ecdysis of the provisional cuticle. These morphogenetic aberrations were very similar to those obtained after treatment of S. gregaria eggs with exogenous juvenile hormone (JH). Investigation of the JH synthetic activity of corpora allata from aging females of each phase revealed a marked increase in the rates of JH synthesis in comparison with those of young females of the same phase. Furthermore, injection of JH into young females increased the proportion of embryos showing inhibited development from 7% (in control females) to 30% (in JH-treated females). These results suggest a possible correlation between reduced viability of eggs and high rates of JH synthesis in aging S. gregaria of both phases.

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