Siblicidal behaviour by larvae of the gregarious parasitoid Cotesia vanessae


Hervet, V.A.D., Laird, R.A., Floate, K.D. (2018). Siblicidal behaviour by larvae of the gregarious parasitoid Cotesia vanessae. Journal of Hymenoptera Research,(67), 55-62.

Plain language summary

Cotesia vanessae is a parasitic wasp that lays up to 150 eggs in a single host caterpillar. 'Flooding' the host with eggs increases the likelihood of overwhelming the host's defenses, but it also increases competition among wasp larvae for food resources.
This research shows that the wasp larvae will actively kill each other inside the host to reduce competition for available food. Cotesia vanessae is of interest as a natural enemy of many species of cutworms (Lepidoptera: Noctuidae) that are pests of agricultural crops.


Contrasting life histories distinguish solitary from gregarious parasitoids. Females of solitary species typically lay one egg in a host; when more than one parasitoid is present in the host, larvae will kill their rivals so that only one parasitoid completes development. Females of gregarious species typically lay multiple eggs in the same host with the resultant larvae co-existing to complete development. Here we provide an unusual report of siblicide by larvae of a gregarious parasitoid; i.e., Cotesia vanessae (Reinhard) (Hymenoptera: Braconidae) developing in noctuid caterpillars (Lepidoptera). Siblicidal behaviour has not previously been reported with larvae of gregarious Braconidae. We speculate that this behaviour reflects a trade-off between the finite amount of resources within the host available for larval development, and selection to optimize use of these resources. ‘Flooding’ the host with eggs allows the female to use the finite resources of the host to their fullest extent, regardless of host size. This strategy also may allow the female to overwhelm the host’s immune system to enhance survival of her progeny in otherwise marginal host species. It further may enhance the ability of the female’s progeny to competitively exclude the larvae of conspecific females or larvae of other parasitoid species co-occurring in the host. Siblicide allows for self-regulation of brood size when host resources are insufficient to support egg-to-adult development of all eggs initially laid in the host.