Examination and revision of the larval life history of Microplitis croceipes (Hymenoptera: Braconidae)

•Microplitis croceipes is an endoparasitoid of Heliothis virescens larvae.•M. croceipes larvae pass through five instars.•The final parasitoid larval molt occurs during egression from the host.•The exuvium from the final molt plugs the egression wound to prevent host bleeding.•The host remains alive and responsive to stimulation during parasitoid pupation.

Microplitis croceipes (Braconidae) is a solitary parasitoid of Heliothis virescens (Noctuidae), the tobacco budworm. The larva of M. crocepies develops within the abdominal cavity of its host while the host remains active. Larval development culminates with egression of the larva from its host, and subsequent cocoon spinning and pupation near the host’s body. Previous research indicated that M. croceipes larvae pass through three instars within the host, followed by egression and pupation. Head capsule measurements recorded in this study at several intervals during larval development revealed that the larvae of M. croceipes pass through five instars. The final molt, i.e. into the fifth instar, occurs during larval egression from the host, and the shed exuvium remains lodged in the egression wound, acting as a plug that prevents exsanguination of the host. The host remains alive through parasitoid pupation, and may play a defensive role guarding the parasitoid cocoon during its development to the adult stage.

Graphical abstractPenultimate-instar parasitoid larva egressing from its host. (a) The fourth-instar parasitoid larva (broken outline) rasps and thins the host’s integument until the cuticle breaks, and the larva can begin to push its way through the host’s abdominal wall. (b) Here, the parasitoid larva emerges at the host’s sixth abdominal segment (A6). (c) As it egresses from its host, the parasitoid larva molts a final time; the shed exuvium (Ex.) remains attached to the egression wound (Eg.) acting as a plug to prevent host hemorrhaging. A1 is the first abdominal segment, and T1 is the first thoracic segment.Figure optionsDownload full-size imageDownload as PowerPoint slide