SUPPRESSION OF JUVENILE-HORMONE ESTERASE IN HELIOTHIS-VIRESCENS BY MICROPLITIS-DEMOLITOR CALYX FLUID

Microplitis demolitor is a polydnavirus-carrying braconid wasp that pa rasitizes the larval stage of Heliothis virescens. Previous studies in dicated that parasitized hosts exhibit developmental arrest whereas la rvae injected with either M. demolitor calyx fluid or polydnavirus (Md PDV) form larva-pupal intermediates. Here we investigated the role of teratocytes in altering host development and the effects of calyx flui d on juvenile hormone esterase activity in H. virescens. Injection of superphysiological doses of teratocytes or coinjection of a physiologi cal dose of teratocytes and calyx fluid affected fourth-stadium host d evelopment similarly to parasitism, but parallel injections had lesser effects in fifth-stadium hosts, Juvenile hormone (JH) titers in paras itized, fifth-stadium H. virescens were 13-fold higher by 60 h post-pa rasitism than those in controls. Unparasitized H. virescens exhibited two peaks of JH metabolic activity in the last instar, one at 60 h aft er larval ecdysis and the other just before pupation (132 h post-ecdys is), whereas JH metabolism was completely suppressed in parasitized an d calyx fluid-injected hosts. The effect of calyx fluid on JH metaboli sm was independent of the presence of teratocytes and, based on genera l esterase assays, was specific for JH esterase. Experiments using hem olymph from parasitized larvae suggested that the reduction in host JH esterase activity was not due to a factor in the hemolymph.