Multi-Species Host Use by the Parasitoid Fly Ormia lineifrons

SIMPLE SUMMARY: Species interact with each other in many ways, such as predation, mutualism, or competition, ultimately affecting each other’s evolution, reducing the negative effects of these interactions and/or increasing the positive ones. We studied a parasitic fly that uses different katydid species as hosts for its larvae sequentially at different times during its breeding season. The fly larvae kill the host when they emerge, setting up multiple arms races between the fly and each of the hosts. The hosts are selected to ameliorate the negative impact of parasitism, whereas the parasitoid is selected to use all host species well for the population to persist. We compared host use and the ability of fly pupae to develop into adults across four katydid hosts. The parasitism rate varied between ~14% and 73%, yet host use was similar for many larval measurements across hosts. However, one species was a particularly poor host for the fly based on fly pupa development. We suggest that currently, this poor host strongly influences the evolution of the fly in this arms race to improve its utilization of this host. Understanding how species interact and affect each other is important to predict their evolution and manage species of human relevance, such as parasites, plant pests, or vectors of disease. ABSTRACT: Antagonistic species relationships such as parasitoid/host interactions lead to evolutionary arms races between species. Many parasitoids use more than one host species, requiring the parasitoid to adapt to multiple hosts, sometimes being the leader or the follower in the evolutionary back-and-forth between species. Thus, multi-species interactions are dynamic and show temporary evolutionary outcomes at a given point in time. We investigated the interactions of the multivoltine parasitoid fly Ormia lineifrons that uses different katydid hosts for each of its fly generations sequentially over time. We hypothesized that this fly is adapted to utilizing all hosts equally well for the population to persist. We quantified and compared the fly’s development in each of the four Neoconocephalus hosts. Cumulative parasitism rates ranged between ~14% and 73%, but parasitoid load and development time did not differ across host species. Yet, pupal size was lowest for flies using N. velox as a host compared to N. triops and other host species. Successful development from pupa to adult fly differed across host species, with flies emerging from N. triops displaying a significantly lower development success rate than those emerging from N. velox and the other two hosts. Interestingly, N. triops and N. velox did not differ in size and were smaller than N. robustus and N. nebrascensis hosts. Thus, O. lineifrons utilized all hosts but displayed especially low ability to develop in N. triops, potentially due to differences in the nutritional status of the host. In the multi-species interactions between the fly and its hosts, the poor use of N. triops may currently affect the fly’s evolution the most. Similarities and differences across host utilization and their evolutionary background are discussed.