Invasive <i>Drosophila suzukii</i> facilitates <i>Drosophila melanogaster</i> infestation and sour rot outbreaks in the vineyards

Abstract

How do invasive pests affect interactions between members of pre-existing agrosystems? The invasive pest <i>Drosophila suzukii</i> is suspected to be involved in the aetiology of sour rot, a grapevine disease that otherwise develops following <i>Drosophila melanogaster</i> infestation of wounded berries. We combined field observations with laboratory assays to disentangle the relative roles of both <i>Drosophila</i> in disease development. We observed the emergence of numerous <i>D. suzukii</i>, but no <i>D. melanogaster</i> flies, from bunches that started showing mild sour rot symptoms days after field collection. However, bunches that already showed severe rot symptoms in the field mostly contained <i>D. melanogaster</i>. In the laboratory, oviposition by <i>D. suzukii</i> triggered sour rot development. An independent assay showed the disease increased grape attractiveness to ovipositing <i>D. melanogaster</i> females. Our results suggest that in invaded vineyards, <i>D. suzukii</i> facilitates <i>D. melanogaster</i> infestation and, consequently, favours sour rot outbreaks. Rather than competing with close species, the invader subsequently permits their reproduction in otherwise non-accessible resources and may cause more frequent, or more extensive, disease outbreaks.