Biochemical and metabolic alterations in Acyrthosiphon pisum parasitized by Aphidius ervi

Abstract

AbstractBiochemical and metabolic alterations in Acyrthosiphon pisum (Harris) (Homoptera: Aphididae) parasitized by the endophagous Aphidius ervi Haliday (Hymenoptera: Braconidae) are reported. Total ecdysteroid titer was determined by radioimmunoassay. The hemolymph levels of acylglycerols and proteins were assessed with an enzymatic method and Bradford's method, respectively. Alterations of the electrophoretic pattern of host hemolymph proteins were assessed by SDS‐PAGE. Analyses were carried out on hosts parasitized as 1st instars, as well as on hosts which were parasitized later, as 3rd or 4th instars. Parasitism did not significantly alter the ecdysteroid titer of pre‐adult stages when parasitized as 3rd instars. In contrast, the ecdysteroid titer in developmentally arrested 4th instars of A. pisum, previously parasitized as 1st instars, was significantly lower than in the case of synchronous nonparasitized controls. Ecdysteroids were detected also in adult aphids, which, when previously parasitized as 3rd instars, showed a precocious end of reproductive activity associated with a hormonal titer that was significantly lower than in actively reproducing nonparasitized controls of the same age. Acylglycerol and protein titers were significantly higher in the hemolymph of both early and late parasitized hosts, 5–6 days after parasitoid oviposition. SDS‐PAGE analysis of hemolymph collected 5 days after parasitization revealed the presence of both upregulated proteins and of parasitoid‐specific proteins. The observed biochemical changes in parasitized hosts were synchronized with the major part of parasitoid larval growth and, apparently, strictly related to parasitic castration of the host. The role and importance of host regulation factors controlling these biochemical and developmental alterations in parasitized pea aphids are discussed. © 1995 Wiley‐Liss, Inc.