The sweet tooth of parasitoids: a meta-analysis exploring the floral resources of hymenopteran parasitoids

Background/Question/Methods

Hymenopteran parasitoids (hereafter ‘parasitoids’) are a very diverse group of organisms and play important roles in food webs worldwide (affecting host behavior and population dynamics) and as biological control agents. As larvae, parasitoids feed on their hosts. Recently, the importance of sugar in the diet of adult parasitoids has come to light. Simple sugars, most commonly obtained from floral nectar, can enhance longevity, fuel egg development and dispersal ability, and ultimately increase the rates of parasitism in the field. While floral nectar is now known to be a very important resource for parasitoids, relatively little is known about parasitoid-food plant relationships in natural systems. We used a meta-analysis approach to begin to understand these relationships in greater detail. We compiled data from studies explicitly reporting floral nectar feeding by parasitoids that reported both parasitoid and food-plants to the species level. We investigated patterns of interactions between taxa to test our hypothesis that there are non-random associations between parasitoids and their food plants.  

Results/Conclusions

The dataset includes more than 600 observations of parasitoids foraging on floral nectar, comprised of over 240 parasitoid species from 17 families and 130 plant species from 32 families. The geographic range includes Canada, France, Hungary, New Zealand, the United Kingdom, and the United States. The observations range from temperate to arctic latitudes.

The most over-represented plant families in the dataset were Apiaceae and Asteraceae. These families are characterized by generalist pollination syndromes, suggesting their generalized form are not only exploited by pollinators but are used by parasitoids too. The most over-represented parasitoid families were Ichneumonidae, Braconidae, Eulophidae, and Pteromalidae, all of which visited numerous plant families (including Apiaceae and Asteraceae). There were many families of parasitoids that visited only one plant family. However, because the studies provide presence-only data, we cannot yet ascertain whether parasitoids are specialist floral foragers.

Future directions include adding more studies to the dataset (after they have been uncovered), adding floral trait data and testing for non-random associations between parasitoids and plants using statistical methods for presence-only data. This information can not only inform us of the natural history of an extremely diverse group of organisms, but also inform important management decisions in agroecosystems to support parasitoids.