|Beckage, Nancy - DEPT.ENT. U OF CA.USA|
Submitted to: Society for Experimental Biology Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: July 1, 2000
Publication Date: N/A
Technical Abstract: Tobacco hornworm larvae parasitized by Cotesia congregata under go many physiological changes, especially during their last instar. Through a manipulation of host hormone levels, the parasitoid causes host development to be halted in the last larval stage. Host hemolymph juvenile hormone titers are dramatically elevated, JH esterase is undetectable and PTTH and other neuropeptides accumulate in the brain, ventral nerve cord, and midgut endocrine cells. Hindgut ecdysiotropic hormone levels also appear elevated in parasitized larvae, and the host's prothoracic glands appear refractory to PTTH. Thus, it is not surprising that hemolymph ecdysteroid titers remain relatively low. However, the parasitoid induces a small ecdysteroid peak just prior to and during its last larval molt and concomitant emergence from the host, and additional ecdysteroid peaks occur following emergence. The application of 200 micrograms of methoprene to final instar day 2 larvae delays emergence of the wasps from the host, and likewise delays the emergence-associated ecdysteroid peak. Few wasps emerge from methoprene-treated hosts, and the wasps which do emerge do not metamorphose normally, and die within the pupal cocoon.