Synthesis/release of ecdysteroids by Cotesia congregata, a parasitoid wasp of the tobacco hornworm, Manduca sexta.

摘要

In vitro incubation was used to characterize the synthesis and release of ecdysteroids [moulting hormones] by Cotesia congregata, a parasitoid of the tobacco hornworm, Manduca sexta. In addition, physical characteristics were identified as markers for tracking parasitoid moulting hormone content as well as hormone synthesis and release. Moulting hormone content of whole body homogenates increased with parasitoid age. Body length, anal vesicle size and time of ecdysis were more precise indicators oftimes when moulting hormone content would be high or low. Moulting hormone levels peaked at the time of the parasitoid's moult from the 1st- to the 2nd-instar and again in the largest parasitoid's that were preparing for their moult to the 3rd-instar. Moulting hormone synthesis and release also increased with parasitoid age. When body length was the independent variable, synthesis and release peaked in larvae that were 3.0 mm (often undergoing a moult), dipped in larvae that were 3.6 mm (post-moult), and rose again as larvae increased in length. Ecdysone, 20-hydroxyecdysone and polar ecdysteroids were the predominant moulting hormones released on days 1-4. Thus, a moulting hormone known to be physiologically active is released by the parasitoid. Thisis the first time that a precise, detailed system of markers has been identified for tracking C. congregata development. These results support the view that parasitoid synthesis and release of moulting hormones are associated with specific events in theparasitoid's life cycle, and can be predicted by selected physical markers including parasitoid size and instar, size/degree of ballooning of the anal vesicle, and shedding of the 1st instar cuticle.