Effects of a juvenile hormone analog, methoprene, on the hemolymph titers of biliverdin-binding proteins in the common cutworm, Spodoptera litura (Lepidoptera: Noctuidae).

Abstract

Effects of methoprene (a juvenile hormone analog) on the larval development and hemolymph titers of biliverdin-binding proteins (BPs) in Spodoptera litura were studied. BP-A first appeared in the hemolymph of the fifth (penultimate) instar larvae, decreased during the molting to the sixth instar and prominently increased during the sixth (last) instar. On the other hand, the titer of BP-B, a predominant component in preceding stadia, greatly increased during the fifth instar, drastically decreased before the ecdysis to sixth instar, and slightly increased during the sixth (last) instar. Methoprene (0.1–5 μg/insect) topically applied on day 0 of the fifth instar caused little effect on the duration of the fifth instar and on the titers of BPs, while the application to day 0 sixth instars extended the last instar dose-dependently and changed the BP titers as follows: BP-A showed a similar increase as in untreated control, but continued to increase further during the prolonged feeding period; BP-B titer showed a increase within one day of the application. Double applications of methoprene at one day interval induced a stepwise increase of the BP-B titer at each application, but not of BP-A. These results suggest that BP-B synthesis is triggered by juvenile hormone, which also regulates the synthesis of BP-A indirectly by blocking larval-pupal transformation.