Inter- and intraspecific competition of parasitic wasps: Does host experience influence wasp competition?

Background/Question/Methods

Predators and parasites can compete for prey in several ways; they can race to utilize prey before their competitor can reach it, and they can interfere with one another’s foraging efficiency. One way to interfere with a competitor’s foraging efficiency is to trigger defensive behaviors in the shared prey. The soybean aphid is a suitable host to the parasitic wasps Binodoxys communis and Lysiphlebus testaceipes, but its defensive response to each wasp species is distinct. To evaluate how the wasps compete when sharing a colony of aphids, two experiments were conducted. First, we sequentially exposed a group of aphids to one wasp and then another and recorded foraging behaviors of the wasp and defensive behaviors of the aphids. From this experiment, we quantified the differences in wasp foraging and aphid defenses when wasps were attacking aphid groups that had never encountered wasps, were primed with B. communis, or were primed with L. testaceipes. Then, we exposed colonies of aphids to two wasps simultaneously and recorded the number and species of wasps that emerged from the parasitized colony to measure overall inter- and intraspecific competition between the wasps.

Results/Conclusions

The behavior experiment suggested that B. communis is unaffected by priming with another wasp; the frequency of encounters with aphids and stings was not different between B. communis foraging in naïve aphid groups, aphid groups primed by another B. communis, or aphid groups primed by L. testaceipes. L. testaceipes, on the other hand, encounters and stings more rapidly when aphids are primed with B. communis but less vigorously when they are primed with another L. testaceipes compared to when foraging in naïve aphid groups. In the second experiment, a pair of B. communis parasitized twice as many aphids as a single B. communis paired with a L. testaceipes, indicating that intraspecific competition equaled interspecific competition. However, L. testaceipes parasitized far more aphids when paired with another L. testaceipes than when paired with a B. communis, suggesting stronger interspecific competition than intraspecific competition. The results of the two experiments concerning L. testaceipes appear contradictory; priming by one L. testaceipes decreases stinging rate of another, but two together parasitize aphids far more efficiently than one with a B. communis. These conflicting results illustrate that studying both population dynamics and individual behavior can reveal the details of complex species interactions.