Exploring effects of arthropod-infecting pathogens on pollination: A meta-analysis

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Rover Bernhard, Isabella Ng, Katherine Garcia, Maisy Feeley, Wilnelia Recart and Arietta Fleming-Davies, Biology, University of San Diego, San Diego, CA

Background/Question/Methods
While the majority of prior research on interspecific interactions has focused on pairwise interactions, no interaction occurs in isolation, and thus it is essential to consider the tritrophic interactions that result from direct and indirect interactions between multiple species. For example, the arthropods that pollinate plants can also be infected with pathogens, which have the potential to affect pollination services. Although arthropod pollination and disease have both been extensively studied, there is little research on the intersection of the two. Pathogens of arthropods have the potential to disrupt the pollination process by affecting pollinator population density or traits relevant to pollinator effectiveness. Pathogens may also infect insect herbivores and thus reduce herbivory damage, therefore allowing a plant to allocate more resources to the production of flowers and floral rewards. We conducted a meta-analysis to 1) summarize the existing literature on the effects of pathogens on arthropod pollinators and herbivores and 2) quantify the extent to which pathogens affect arthropod population density, physiology, morphology, and behavior, with potential repercussions for pollination.
Results/Conclusions
We reviewed 2201 published articles from targeted Web of Science searches and found 79 articles that fit our criteria for inclusion. From these articles, we extracted 227 measures (mean and SE) of pollination-relevant traits for 33 different pathogens in 34 different arthropod species from 31 different genera (seven orders). Studies were fairly evenly distributed across pathogen types (Fisher’s exact test, p=0.652), with the exception of bacteria, which were underrepresented compared to multicellular parasites, fungal, and viral pathogens (bacteria: 3% of total; 30% each for fungal and viral pathogens; 37% for parasites, n=79 studies). However, particular pathogen types were more heavily studied in certain insect orders (Fisher’s exact test, p<0.001), with 19 of 29 studies of viral pathogen effects conducted in Lepidoptera (primarily in herbivores), and 14 of 22 studies of fungal pathogens conducted in Hymenoptera (primarily in pollinators). Preliminary results also suggest strong effect sizes of pathogen exposure in population-density traits (e.g., fecundity, survival) across studies as measured by Hedges g. Overall, our results suggest that in spite of extensive data on how pathogens affect pollinators, most studies are focused on a select few pathogens and hosts. Future work is needed to directly measure the effects of insect pathogens on pollinator effectiveness, particularly in Lepidoptera that function as both herbivores and pollinators.