Interrelationships between Growth of Heliothis virescens (Lepidoptera: Noctuidae) and That of its Parasitoid, Campoletis sonorensis (Hymenoptera: Ichneumonidae)

Abstract

A statistically significant positive linear correlation was observed between the initial weight (weight at the time of parasitization) of Heliothis virescens (F.) larvae and the weight of adult Campoletis sonorensis (Cameron) that emerged from them. This relationship was not observed within a stadium but was influenced by the host instar at the time of parasitization; this indicated that the adult weight-host weight relationship was mediated through hosts of different instars rather than being different in absolute weight. Parasitized second, third, and fourth host instars attained their maximal weights in 3-5 d; their weights then decreased. In contrast, parasitized first-instar hosts increased in weight for 7-9 d until they died, before the parasitoid larvae emerged; these hosts attained a significantly lower maximal weight despite their longer period of weight gain. Development time of the parasitoid was not significantly affected by the host instar attacked. The percentage parasitoid emergence from host fourth instars was significantly lower than that from the other three instars, partly because of unsuccessful oviposition and partly because of the failure of the mature parasitoid larvae to emerge from their host fourth instar. Host larvae containing female parasitoids attained a significantly higher mean maximal weight than those containing males. The weights of adult female parasitoids were positively correlated with fecundity.