PARASITISM BY MICROPLITIS-DEMOLITOR INDUCES ALTERATIONS IN THE JUVENILE-HORMONE TITERS AND JUVENILE-HORMONE ESTERASE-ACTIVITY OF ITS HOST, PSEUDOPLUSIA-INCLUDENS

Microplitis demolitor is a polydnavirus-carrying parasitoid that attac ks the larval stage of Pseudoplusia includens and other noctuids. Para sitism or injection of wasp components like polydnavirus and teratocyt es has a juvenilizing effect on P. includens development. Here we meas ured hemolymph juvenile hormone (JH) titers and juvenile hormone ester ase activity in P. includens larvae after parasitism or injection of w asp components. Results were compared to nonparasitized larvae. During the fifth stadium, JH titers of nonparasitized larvae fluctuated betw een 0.08 and 0.50 ng/ml, whereas titers in parasitized larvae never fe ll below 2 ng/ml. P. includens larvae injected with calyx fluid plus v enom or calyx fluid plus venom and teratocytes exhibited JH titers int ermediate between parasitized and nonparasitized larvae. Nonparasitize d larvae exhibited two peaks of JH esterase activity. The first occurr ed between 12 and 48 h in association with cessation of larval feeding , while the second occurred immediately before pupation. In contrast, levels of JH metabolism remained at low levels in parasitized larvae a nd larvae injected with calyx fluid plus venom or calyx fluid, venom a nd teratocytes. Only trace amounts of JH were detected in irt vitro as says of teratocytes or M. demolitor larvae suggesting neither released JH into the hemolymph of parasitized larvae. Although calyx fluid plu s venom and teratocytes did not elevate JH titers to the levels measur ed in parasitized larvae, their effects on formation of larval-pupal i ntermediates by P. includens were similar to those generated by exogen ous application of methoprene or JH.