RESUMO
Grape sour (bunch) rot is a polymicrobial disease of vineyards that causes millions of dollars in lost revenue per year due to decreased quality of grapes and resultant wine. The disease is associated with damaged berries infected with a community of acetic acid bacteria, yeasts, and filamentous fungi that results in rotting berries with high amounts of undesirable volatile acidity. Many insect species cause the initial grape berry damage that can lead to this disease, but most studies have focused on the role of fruit flies in facilitating symptoms and vectoring the microorganisms of this disease complex. Like fruit flies, social wasps are abundant in vineyards where they feed on ripe berries and cause significant damage, while also dispersing yeasts involved in wine fermentation. Despite this, their possible role in disease facilitation and dispersal of grape rots has not been explored. We tested the hypothesis that the paper wasp Polistes dominulus could facilitate grape sour rot in the absence of other insect vectors. Using marker gene sequencing we characterized the bacterial and fungal community of wild-caught adults. We used a sterilized foraging arena to determine if these wasps transfer viable microorganisms when foraging. We then tested if wasps harboring their native microbial community, or those inoculated with sour rot, had an effect on grape sour rot incidence and severity using a laboratory foraging arena. We found that all wasps harbor some portion of the sour rot microbial community and that they have the ability to transfer viable microorganisms when foraging. Foraging by inoculated and uninoculated wasps led to an increase in berry rot disease symptom severity and incidence. Our results indicate that paper wasps can facilitate sour rot diseases in the absence of other vectors and that the mechanism of this facilitation may include both increasing host susceptibility and transmitting these microbial communities to the grapes. Social wasps are understudied but relevant players in the sour rot ecology of vineyards.
RESUMO
Actinomycetes-a group of antimicrobial producing bacteria-have been successfully cultured and characterized from the nest material of diverse arthropods. Some are symbionts that produce antimicrobial chemicals found to protect nest brood and resources from pathogenic microbes. Others have no known fitness relationship with their associated insects, but have been found to produce antimicrobials in vitro. Consequently, insect nest material is being investigated as a new source of novel antimicrobial producing actinomycetes, which could be harnessed for therapeutic potential. To extend studies of actinomycete-insect associations beyond soil-substrate dwelling insects and wood boring excavators, we conducted a preliminary assessment of the actinomycetes within the nests of the paper wasp, Polistes dominulus (Christ). We found that actinomycetes were readily cultured from nest material across multiple invasive P. dominulus populations-including members of the genera Streptomyces, Micromonospora, and Actinoplanes. Thirty of these isolates were assayed for antimicrobial activity against the challenge bacteria Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, Serratia marcescens, and Bacillus subtilis. Sixty percent of isolates inhibited the growth of at least one challenge strain. This study provides the first assessment of bacteria associated with nests of P. dominulus, and the first record of antimicrobial producing actinomycetes isolated from social wasps. We provide a new system to explore nest associated actinomycetes from a ubiquitous and cosmopolitan group of insects.
