Parasitoid tachinid fly, Celatoria setosa, reduces performance, oviposition, and pheromone emission in herbivore pest, Acalymma vittatum.

Interactions between parasitoids and herbivore hosts are complex as parasitism affects multiple components of host behavior and fitness through both consumptive and non-consumptive effects. Understanding how these multiple effects unfold is especially important in applied systems where parasitoids play a role in biological control. In lab-based experiments, we manipulated parasitism in striped cucumber beetles, Acalymma vittatum (Coleoptera: Chrysomelidae), a major pest of cucurbits in North America, using Celatoria setosa (Diptera: Tachinidae) to assess how parasitism affected multiple components of male and female fitness, including survival, herbivory, oviposition, and reproductive signaling through the emission of vittatalactone, a male-specific aggregation pheromone. In follow-up experiments, we investigated the potential non-consumptive effects of parasitoids on these metrics by exposing beetles to arenas with or without parasitoids. Parasitized female beetles experienced a 4-fold increase in mortality, consumed 49.6% less leaf tissue, and were less likely to oviposit eggs compared to non-parasitized control females. In addition, parasitized males in small groups emitted 52.5% less vittatalactone than non-parasitized control males. Lastly, we found some evidence of non-consumptive effects of parasitoids in which individual females and groups of males, exposure to parasitoids resulted in reduced foliar damage. Our findings highlight broad effects of tachinid parasitoids in a common pest and point to multiple mechanisms for reduced pest performance.