Assessing Drosophila suzukii as a vector of Caneberry fruit rot pathogens

Interactions between plant pathogenic fungi and frugivorous insects can play an important role in fruit disease epidemiology. Feeding and/or oviposition wounds create opportunities for fungal colonization, and adults can increase disease incidence by passively dispersing fungal propagules. In caneberries, these vectoring interactions may amplify damage from the invasive pestiferous vinegar fly, Drosophila suzukii (spotted-wing drosophila). Periods of peak D. suzukii activity overlap with several primary fruit rot pathogen, particularly Botrytis cinerea and Cladosporium cladosporioides, and larvae are known to co-occur with and feed on both Botrytis and Cladosporium at low rates. To advance our understanding these interactions, we surveyed the filamentous fungal community associated with adult D. suzukii, isolating and molecularly identifying fungi from field collected adults over three years. Survey results indicate that D. suzukii associate with a rich fungal community, with some flies found to be carrying known pre-harvest pathogens. Most fungi were detected infrequently; the most commonly isolated genera (Cladosporium and Aspergillus) occurred on less than 50% of the flies sampled, suggesting that D. suzukii do not form tight associations with specific fungal taxa. Instead, flies may unintentionally acquire fungal spores while landing or feeding on infected fruit. Laboratory assays also demonstrated that D. suzukii are capable of transmitting fungi to sterile media. Together, these results suggest a passive vectoring relationship between D. suzukii and fruit rot fungi. Deepening our understanding of these interactions is necessary to integrate insect and pathogen management programs for raspberry production.