Cucurbit yellow vine disease is caused by the phloem-inhabiting bacterium, Serratia marcescens. Now known to occur in over 12 states, S. marcescens infects melons, squash, and pumpkins, but not cucumbers. The natural vector is a common pest of cucurbits, the squash bug, Anasa tristis. Normally a xylem tissue drinker, A. tristis also probes the phloem, and it is thought that it acquires and transmits S. marcescens when probing phloem tissues. Transmission data using artificial feeding sachets show that A. tristis can transmit S. marcescens intermittently from 24 hr up to 3 wk after acquisition. Experimentally, three of five leafhopper species, but not the five aphid species tested, can transmit S. marcescens using artificial feeding sachets, suggesting some degree of vector specificity. Lygus hesperus was also tested and found to be an experimental vector of S. marcescens. In our effort to understand the relationship between S. marcescens and its natural and experimental vectors, we are testing the transmission efficiencies of S. marcescens isolates from different ecological niches, the pathogenicity of those same isolates to the field vector, A. tristis, and determining if this bacterium follows a circulative path through the body of A. tristis as opposed to adhering to and colonizing the foregut