Multi-trophic interactions are integral to understanding community ecology. While most studies examine the first, second, and third trophic levels, less attention has been given to higher trophic level interactions. Nearly every herbivorous insect is attacked by a parasitoid insect, which in turn is parasitized by hyperparasitoid wasps that cause mortality, affect behavior, and influence life history traits of parasitoids. Cotesia glomerata is a parasitoid wasp with a wide geographic distribution and it is a major parasitoid of pierid caterpillars that are common herbivores in many ecosystems. Although much is known about C. glomerata behavior and ecology, less is known about the different hyperparasitoids attacking C. glomerata in its different localities. We investigated whether different C. glomerata populations experience unique communities of hyperparasitoids and how these top-down interactions affect clutch size decisions and sex ratios of C. glomerata in Colorado. Hyperparasitoids were reared or dissected from C. glomerata broods collected from six field sites in Colorado. The diversity of hyperparasitoids attacking C. glomerata in Colorado was compared with hyperparasitoids communities in the eastern US and in Europe. We examined how hyperparasitoids affected brood size and sex ratios of C. glomerata. GLM and OLS regression were used to analyze the data.
Results/Conclusions
We found 11 species of hyperparasitoid wasps that attacked C. glomerata with one species, Trichomalopsis dubia, that has never before been identified as a hyperparasitoid of C. glomerata. Four of the 11 hyperparasitoids also attack C. glomerata in Virginia, but have not been observed attacking C. glomerata in Europe. Of the 11 hyperparasitoids, only Baryscapus galactopus occurs in North America and Europe. The probability of hyperparasitism and proportion of C. glomerata males in a brood increased as brood size increased. More adult C. glomerata were found in unparasitized broods than in hyperparasitized broods. Our results indicate that different C. glomerata populations are attacked by a unique set of hyperparasitoids. Furthermore, top-down effects from hyperparasitoids impact survivorship and sex ratios of C. glomerata. These observations suggest that hyperparasitoids can indirectly affect trophic and non-trophic (e.g., competition) interactions leading to population changes in parasitoids. If different populations of parasitoids experience their own community of hyperparasitoids, there could be a mosaic of evolutionary and ecological relationships across a broad landscape. Within a complex food web, there are numerous relationships between species and our attention to interspecific interactions at higher trophic levels improves our understanding of community ecology.