Fitness-related traits in a parasitoid fly are mediated by effects of plants on its host

Plants can affect parasitoids directly, by reducing or enhancing their ability to locate hosts, or indirectly by affecting the fitness of herbivores and thus of parasitoids. Tritrophic interactions between three host plants (cucumber, tomato, sweet pepper), a polyphagous herbivore Trichoplusia ni and a generalist parasitoid Compsilura concinnata were assessed. Plants had a strong effect on T. ni larval survival, as well as on C. concinnata fitness-related traits: cucumber-fed hosts yielded parasitoids with shorter larval development time and females had heavier pupal weights than parasitoids from host larvae that were fed tomato. Furthermore, C. concinnata was more efficient at finding cucumber-fed than tomato-fed T. ni. These results suggest that C. concinnata has different efficiency and potential as a biocontrol agent on the different crops. This highlights the importance of assessing tritrophic interactions in systems where an inundative biological control agent may be released against generalist targets on more than one crop plant.