Don’t wilt, frass happens: a new vector, Acalymma trivattatum, provides potential geographic expansion of bacterial wilt of cucurbits

The striped cucumber beetle, Acalymma vittatum, is a major cucurbit pest and the known vector of the causal agent of bacterial wilt of cucurbits, Erwinia tracheiphila.  Currently, the pathogen occurs in the Northeastern and Central United States with controls often relying on insecticides to slow transmission by the beetle.  There is a growing concern that E. tracheiphila could expand its geographic range to the Southern and Western United States by other vector species.  One such species is the western striped cucumber beetle (Acalymma trivittatum), a closely related diabroticite beetle that is found along the west coast and into the southwestern portion of the United States. E. tracheiphila risk was assessed by determining the vector competence of A. trivattatum.  Beetles acquired the bacteria via ingestion and frass was collected across time.  Frass was plated for live culture growth, and DNA from both frass and cultures were tested via polymerase chain reaction for presence of E. tracheiphila.  The western striped cucumber beetle transmission rate was analyzed for competence and compared to the known vector, A. vittatum.  We found that the western striped cucumber beetle is a competent vector of E. tracheiphila, and thus has both the ecological and biological properties that could provide a mechanism for geographical expansion of the bacterial wilt of cucurbits.