Serratia marcescens is the causal agent of Cucurbit Yellow Vine Disease (CYVD) which is transmitted in nature by the squash bug Anasa tristis. Aphids were used as model organisms in this experiment to test for pathogenic effects of S. marcescens. Four strains of S. marcescens were tested on the pea aphid Acyrthosiphon pisum. Aphids were fed concentrations of 10^8, 10^2, and 0 cfu/ml each of either an insect isolate, a human isolate, a rice endophyte, or CYVD strain ZO1 suspended in 15% sucrose. After a 24 hour acquisition access period, aphids were placed individually on excised fava bean leaves and mortality was assessed for ten days. Aphids fed sucrose only had a lower mortality rate than that of aphids fed S. marcescens for up to four days post-acquisition, suggesting that S. marcescens is pathogenic to the pea aphid.