Acrobasis vaccinii is found predominantly on cranberries where the larvae feed internally on developing berries, consuming several during development. Larvae often engage in contest competition while defending a berry from conspecifics. In laboratory choice tests where both an infested and non-infested fruit were offered, the majority of larvae initially chose the infested fruit, creating competitive interactions that frequently resulted in the loser being cannibalized. The rate of cannibalism following contests on fruit under semi-field conditions was comparable to the lab. The effect of diet on incidence of cannibalism was studied by comparing responses of larvae provided fruits from fertilized, commercial stands of cranberry and from nutrient-poor wild stands. No significant difference was observed. The issue whether cannibalism would offer nutritional benefits was evaluated by comparing development time, final instar weight, and survivorship of larvae provided berries plus conspecific prey to those provided fruit resources alone.