POLYDNAVIRUS OF MICROPLITIS-CROCEIPES PROLONGS THE LARVAL PERIOD AND CHANGES HEMOLYMPH PROTEIN-CONTENT OF THE HOST, HELIOTHIS-VIRESCENS

Polydnaviruses from certain parasitoid Hymenoptera have been reported to interfere with both host immunity and host development. Heliothis v irescens larvae injected with either calyx fluid or sucrose gradient-p urified polydnavirus from Microplitis croceipes (McPDV) gained less we ight than saline-injected larvae. The active feeding portion of the fi fth stadium larva (lime to reach the burrowing-digging stage) was doub led (7.0 vs. 3.4 days) when a 0.25 wasp equivalent (WE) of sucrose gra dient-purified McPDV was injected into a newly ecdysed fifth stadium h ost. Many of the treated larvae were unable to pupate successfully and died at a point of incomplete larval-pupal ecdysis. Pupae that did re sult from the treated larvae weighed significantly less than controls, even at 0.025 WE. The rate of weight gain and extent of delay of deve lopment were dose-dependent; as little as 0.1 WE extended the time of active feeding by 1.5 days and yielded only 25% adults. A 0.05 WE dose yielded 78% adults compared to 95% for controls. The total protein co ntent of hemolymph from individuals injected with McPDV was significan tly less than that of controls at any McPDV dose equal to or greater t han 0.1 WE. SDS-PAGE profiles of hemolymph proteins from control and M cPDV-injected larvae revealed a marked inhibition of the normal accumu lation of storage proteins during the fifth stadium and a lesser reduc tion of serine protease inhibitor protein. Thus, McPDV-injected larvae exhibited some symptoms (less total hemolymph protein and reduced amo unts of storage protein) similar to those shown by both parasitized la rvae and by larvae injected with M. croceipes teratocytes. However, Mc PDV affected development during the active feeding stage of the larva, while teratocytes primarily impacted larvae at the time when larval-p upal transformation processes are initialed. (C) 1995 Wiley-Liss, Inc.