Fitness consequences of cannibalism in the fall armyworm, Spodoptera frugiperda

We investigated the consequences of cannibalism for some correlates of fitn ess in the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae). T he benefits gained by cannibals were ascertained by comparing survival, dev elopment rate, and pupal weight of larvae that had the opportunity to canni balize with those that did not, at two levels of food availability. Larvae in the cannibalism treatments were provided with a conspecific one instar y ounger than themselves on five dates throughout larval development. Canniba lism Tvas frequent; given the opportunity all larvae predated at least one younger conspecific. The frequency of cannibalism was not affected by the s ex of the cannibal or by the availability of alternative food. However, can nibals suffered a significant reduction in survival at both high and low fo od availability. Furthermore, cannibals had a lower pupal weight in the hig h food treatment and a reduced development rate in the low food treatment. The only detectable fitness benefit associated with cannibalism was a posit ive correlation between the number of victims consumed and development rate under conditions of low food availability On balance, cannibalism appears to be costly; alternative explanations for its occurrence in this species a re discussed.