Application of the juvenile hormone analogue methoprene to fifth instar Manduca sexta larvae that are parasitized by Cotesia congregata either delays or totally suppresses the emergence of the wasps on Days 4-5 of the fifth instar, depending on the dose administered and when it is applied. Normally untreated hosts show a pre-emergence hemolymph ecdysteroid peak, which is 3- to 4-fold higher than the prewandering peak detected in unparasitized larvae, the day before the wasps emerge from the host. The application of 200 micrograms of methoprene to host larvae on Day 2 suppresses this ecdysteroid peak, indicating that the host’s JH and ecdyteroid titers are functionally linked. Application on Day 4 fails to completely suppress this peak, but nonetheless the wasps fail to emerge. Levels of JH and ecdysteroid appear to be maintained in a delicate balance in the host in the last instar, facilitating emergence of the wasps from the host.
Species 1: Lepidoptera Sphingidae Manduca sexta (tobacco hornworm)
Species 2: Hymenoptera Braconidae Cotesia congregata
Keywords: juvenile hormone, ecdysteroid
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