Potential steps toward in vitro rearing of the koinobiont parasitoid, Toxoneuron nigriceps (Hymenoptera: Braconidae)

Parasitic Hymenoptera have potential as useful biological control agents, but the necessity of rearing their hosts as well makes mass rearing labor intensive and expensive. The rearing of parasitoids in artificial systems can cut down considerably on time and effort; however, only egg parasitoids and other idiobionts have been completely reared in vitro thus far. Koinobionts have only been partially reared on artificial diets. Toxoneuron nigriceps Viereck (Hymenoptera: Braconidae), a koinobiont endoparasitoid of Heliothis virescens F. (Lepidoptera: Noctuidae), has previously been reared from early 2nd to early 3rd larval instar. However, larvae reared in vitro failed to spin cocoons and pupate. Further studies on development of T. nigriceps from 3rd instar to adulthood may explain why this failure occurred.

After reaching the third and final larval instar, T. nigriceps larvae egress from the host and feed externally on the liquefied remains of the host tissues. This destructive feeding appears to be a critical step in the development of T. nigriceps. Another major step in development is the formation of a cocoon. In the field, T. nigriceps pupates within a subterranean chamber formed by its host. A trial using various common laboratory items has demonstrated that implements that provide a small, enclosed space can be used as artificial pupation chambers by T. nigriceps. Knowing this, it now seems possible that, by providing a substitute for tissue feeding and an artificial pupation chamber, T. nigriceps could be reared beyond 3rd instar in an artificial system.