Augmentative release of two parasitoid species decreased <i>Drosophila</i> hosts without mutual suppression in a vineyard

Abstract Parasitoids are the most diverse natural enemies of herbivorous insects, and multiple parasitoid species often compete for shared resources. Although resource competition was thought to be a key driver shaping parasitoid population dynamics, field experiments testing the role of host competition are still lacking. We investigated whether the augmentative release of two pupal Drosophila parasitoid species ( Trichopria drosophilae and Pachycrepoideus vindemiae ) in the vineyard decreased the emergence rate of the other species. Parasitoid emergence rate, parasitism rate and host mortality were recorded. Our results indicate that releasing T. drosophilae and P. vindemiae resulted in 17.2% and 34.8% higher mortality in Drosophila hosts, respectively, compared to the plots without parasitoid release. However, neither species decreased the emergence rate of the other species. The difference in thermal tolerance and complementary life history traits of studied parasitoids may mitigate the interspecific competition in the field. Our study highlights the importance of exploring parasitoid competition in the field.