EFFECTS OF PARASITISM BY THE BRACONID WASP COTESIA-CONGREGATA ON HOSTHEMOLYMPH-PROTEINS OF THE TOBACCO HORNWORM, MANDUCA-SEXTA

Parasitism by the braconid wasp Cotesia congregata causes major altera tions in the hemolymph proteins of host tobacco hornworm larvae. Earli er studies showed that the total amount of hemolymph protein is reduce d during parasitism, beginning almost immediately after the host is pa rasitized. Simultaneously, parasitism induces synthesis of large amoun ts of novel proteins that appear in the blood as early as 1-2 h post-p arasitization. The present report confirms earlier studies describing the presence of novel proteins in last instar hosts, and also characte rizes the effects of parasitism in altering the titers of several endo genous host hemolymph proteins normally produced by the fat body and o ther tissues. Analysis of hemolymph plasma using SDS-PAGE and densitom etry, as well as immunodiffusion assays, showed that in terminal stage fifth instar host larvae, the titers of serpins and arylphorin were d ramatically reduced relative to the levels of these proteins detected in nonparasitized gate II fifth instar larvae of the same age. The rel ative differences between parasitized and nonparasitized larvae increa sed with time following ecdysis to the fifth instar, so that the day 4 nonparasitized larvae had arylphorin titers of c. 30 mg/ml, whereas p arasitized day 4 larvae with newly emerged wasps had only one sixth th at amount of storage protein circulating in the hemolymph. Similarly, in nonparasitized larvae the hemolymph serpin concentration increased from c. 200 mug/ml (on day 0) to > 600 mug/ml (on day 4) in prewanderi ng gate II larvae, but in parasitized larvae the hemolymph serpin conc entration was maintained in the range of 100-200 mug per ml hemolymph until the pharate third instar parasites emerged from the host larva o n day 4. In contrast, the level of hemolymph lipophorin was unaffected by parasitism, and lipophorin increased from c. 1.3 to > 3 mg/ml duri ng the time interval between days 0 and 4 in both nonparasitized and p arasitized larvae. Hemolymph titers of insecticyanin also were not sig nificantly different in parasitized vs nonparasitized larvae, and in b oth types of larvae the concentration of this pigment decreased by c. 50% during the same time interval when lipophorin was increased signif icantly. Instead of causing a generalized inhibition of host hemolymph protein synthesis, parasitism causes a complex array of changes in th e hemolymph protein profile of Manduca sexta, possibly via the mediati on of hormonal modulators of host protein synthesis, or transcriptiona l or translational regulation of host gene expression by factors assoc iated with the polydnavirus or molecules secreted by the parasites. An other explanation might be that the turnover rates for serpins and ary lphorins differ in parasitized vs unparasitized larvae. These two inte rpretations could not be distinguished on the basis of the data report ed here.