Parasitoid tachinid fly, <i>Celatoria setosa,</i> reduces performance, oviposition, and pheromone emission in herbivore pest, <i>Acalymma vittatum</i>

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.