Crickets groom to avoid lethal parasitoids

Hosts that are infected by parasitoids pay the ultimate cost: death. Here we investigate whether hosts can combat the lethal effects of parasitoids by enhancing their grooming behaviour and removing the parasitoids before they have a chance to enter the host's body. Many field cricket species are stalked and parasitized by gravid females of the parasitoid fly Ormia ochracea. Female parasitoids lay live first-instar larvae (planidia) on and around the cricket. Planidia burrow into the cricket host where they feed and grow. Because parasitism invariably results in host death, there should be strong selection for crickets to avoid being parasitized. We investigated whether field-caught Texas field crickets, Gryllus texensis, groom to avoid parasitism by O. ochracea. We quantified grooming behaviour of crickets when they were in the same area as O. ochracea adults or larvae (proximity avoidance), and following contact between the cricket and O. ochracea adults or larvae (contact avoidance). Crickets did not adjust grooming behaviour when in close proximity to adult gravid female O. ochracea, nor did they avoid planidia-laden grass. Crickets did, however, substantially increase their grooming activity when placed in an arena filled with planidia-laden grass. Furthermore, crickets that groomed more were much less likely to succumb to parasitoid infestation, compared to crickets that groomed less. Our findings suggest that grooming in G. texensis may function as a strong defence against parasitism by O. ochracea.