Comparing pupation chambers formed by healthy tobacco budworm (Heliothis virescens) larvae to those formed by larvae parasitized with the koinobiont, Toxoneuron nigriceps.

Koinobiont parasitoids manipulate their hosts in many ways to make them more suitable for internal development. However, they have also been known to alter host behavior in ways that benefit the parasitoid during external pupation. Some examples include causing hosts to move to suitable locations before parasitoid egression, and causing moribund hosts to stay on, and protect, parasitoid cocoons.

Toxoneuron nigriceps (Hymenoptera: Braconidae), a solitary koinobiont parasitoid, normally pupates within a cocoon. However, T. nigriceps pre-pupae can only form cocoons within small, enclosed spaces. When left on a flat surface, pre-pupae will simply lay down bed of silk, which they can rarely successfully pupate on top of. In the field, T. nigriceps pupates in a subterranean pupation chamber formed by its host, Heliothis virescens (Lepidoptera: Noctuidae). Both healthy and parasitized H. virescens larvae form these chambers in the soil. Since H. virescens pupae differ from T. nigriceps pupae in both size and shape, it may benefit T. nigriceps larvae to manipulate their hosts into forming pupation chambers that better suit their own needs.

In order to determine whether or not T. nigriceps alters the pupation chamber formation behavior of its host, chambers formed in soil by both healthy and parasitized H. virescens larvae will be compared. The parameters to be investigated are shape, depth below soil, volume and silk content of chambers.