Testing adaptive significance of host manipulation with a parasitoid wasp

According to the extended phenotype hypothesis, certain parasites manipulate the host's behaviour which ultimately enhances the transmission of parasite genes into the next generation. The parasitoid wasp Ampulex compressa attacks and stings its cockroach Periplaneta americana host and lays an egg on the cockroach's leg. Before the wasp's oviposition, the stung cockroach engages in excessive self-grooming for about 30 min. The prey location hypothesis posits that self-grooming may allow the wasp to easily locate its host before transporting it to the nest. To test this hypothesis, we manipulated the mobility of the stung cockroach under different spatial constraints. Latencies to locate stung cockroaches with unlimited movement were similar than latencies to locate stung, but motionless cockroaches irrespectively of spatial constraints. Wasps were less willing to lay eggs and seal an entrance to the burrow in treatments with motionless cockroaches which suggests that if the expected reproductive success is low, then parental investment decreases. Our results provide no support for the location hypothesis and call for further experimental investigation of the extended phenotype hypothesis in parasite–host interactions.