Dynamics of Erwinia tracheiphila acquisition and retention by its insect vector, Acalymma vittatum

Erwinia tracheiphila, the causal agent of bacterial wilt disease, is an ecologically and economically important pathogen of wild and cultivated cucurbits. E. tracheiphila is vectored predominantly by the striped cucumber beetle Acalymma vittatum (Coleoptera: Chrysomelidae) in Central Pennsylvania, but the interactions between E. tracheiphila and A. vittatum are not well understood. To address this, we developed a quantitative Real-Time PCR method using a Taqman probe specific to an E. tracheiphila outer membrane protein (OmpA) to examine the acquisition and retention parameters of E. tracheiphila by A. vittatum and the quantitative dynamics of bacterial replication within the beetle’s digestive tract as a function of time post-exposure to infected plants. My frass results show that acquisition of E. tracheiphila by beetles from infected host plants is not different at 24 vs. 3hr exposure times, but retention rate increases for beetles with longer exposure times. The highest absolute E. tracheiphila concentrations in frass are present immediately after exposure to infected plants and lowest 5 days post exposure, and then increase by 4 weeks. Transmission experiments show that bacterial level in frass is an important determinant for inoculation success, indicating the bacterial growth in the beetle digestive tract over time is an important epidemiological parameter in this system. A better understanding of pathogen-vector interactions will allow for improvement of control systems in agricultural settings, which currently depends on broad-spectrum chemical control of vectors or expensive mechanical barriers to keep insects from contacting plants.