Disease virulence may be strongly influenced by social interactions among pathogens, both during the time course of an infection and evolutionarily. Here we examine how spiteful bacteriocin production in the insect-pathogenic bacterium Xenorhabdus nematophila is evolutionarily linked to its virulence. Theory predicts a negative correlation between virulence and spite due to their inverse correlations with pathogen growth. We examined bacteriocin production and growth across 14 experimentally evolved lineages that show faster host-killing relative to their ancestral population. Consistent with theory, these more virulent lineages showed reduced bacteriocin production and faster growth relative to the ancestor. Further, bacteriocin production was negatively correlated with growth across the examined lineages. These results strongly support an evolutionary trade-off between virulence and spiteful bacteriocin production and lend credence to the view that disease management can be improved by exploiting pathogen social interactions.