Juvenile hormone synthesis as related to egg development in neotenic reproductives of the termite Reticulitermes flavipes, with observations on urates in the fat body

Abstract

The relationship between juvenile hormone (JH) synthesis and egg development, which is well documented in cockroaches, is much less studied in their close relatives, the termites. In this study of neotenic reproductives of the subterranean termite Reticulitermes flavipes, in vitro rates of juvenile hormone (JH) synthesis by corpora allata (CA) are related to vitellogenic egg development and the size of CA. The first study compared brachypterous and apterous neotenics in their first cycle of egg development and a second study compared physogastric and non-physogastric brachypterous and apterous neotenics. In both studies, rates of JH synthesis correlated with the size of CA as indicated by their length. Unlike the cockroach in which all basal oocytes are in the same stage of development, those in termites are in various stages. In brachypterous and apterous in the first cycle of egg development, CA with high rates of JH synthesis were from females with early vitellogenic basal oocytes, whereas CA with low rates of JH synthesis were from females with either pre-vitellogenic or mature basal oocytes. This pattern of JH synthesis is similar to the cycle of JH synthesis correlated with oocyte development in several cockroach species. In later oocyte maturations, CA from physogastric apterous females with ovaries containing mature, as well as growing oocytes, showed a wide range of JH production; the CA with the highest rates of JH synthesis were from females with the highest proportion of early vitellogenic oocytes suggesting that both mature and early vitellogenic oocytes interact to regulate JH synthesis. Rates of JH synthesis were related to the number of vitellogenic ovarioles. Physogastric brachypterous neotenics, compared to the other classes of neotenic females, had CA with 2- to 4-fold higher rates of JH synthesis and ovaries with 2.5- to 8-fold greater number of vitellogenic ovarioles. However, both physogastric brachypterous and apterous neotenics had more vitellogenic basal oocytes and less urate in their fat bodies than the respective non-physogastric neotenics. These results demonstrate the similarities and differences between the classes of neotenic termites and between reproductive females in cockroaches and termites.