Dose‐dependent influence of <i>Campoletis sonorensis</i> polydnavirus on the development and ecdysteroid titers of last‐instar <i>Heliothis virescens</i> larvae

Abstract

Abstract Campoletis sonorensis calyx fluid arrests the development of last‐instar Heliothis virescens larvae and is associated with the gross degeneration of the host's prothoracic glands. Through manipulations of ovary supernatant, Campoletis sonorensis polydnavirus (CsV) was found to be the only component of calyx fluid responsible for causing host developmental arrest. Venom from C. sonorensis had no effect on host development. Suspensions of CsV were quantified, and various doses were injected into last‐instar hosts. The percentage of larvae developmentally arrested was dose dependent. In addition, larvae not arrested by injection with CsV suspensions were developmentally delayed in a dose‐dependent manner. Hosts were delayed in the stage in which they were injected and, after recovery, developed at normal rates. Measurements by radioimmunoassay indicated that developmental delay was due to a suppression of ecdysteroid titers. After a dose‐dependent period of suppression, hemolymph ecdysteroid titers recovered and reached titers comparable to those observed in saline‐injected controls. Examination of prothoracic glands from developmentally delayed larvae revealed that partial degeneration occurred. Comparisons of the number and mean size of surviving gland cells and the length of developmental delay suggested that surviving gland cells may compensate for degenerated cells by increasing their ecdysone production.