Fitness consequences of cannibalism in the fall armyworm, Spodoptera frugiperda

We investigated the consequences of cannibalism for some correlatesoffitness in the fall armyworm, Spodoptera frugiperda (Lepidoptera:Noctuidae).The benefits gained by cannibals were ascertained by comparingsurvival,development rate, and pupal weight of larvae that had theopportunityto cannibalize with those that did not, at two levels of foodavailability.Larvae in the cannibalism treatments were provided with aconspecificone instar younger than themselves on five dates throughoutlarvaldevelopment. Cannibalism was frequent; given the opportunityall larvaepredated at least one younger conspecific. The frequencyof cannibalism wasnot affected by the sex of the cannibal orby the availability of alternativefood. However, cannibalssuffered a significant reduction in survival at bothhigh andlow food availability. Furthermore, cannibals had a lower pupalweightin the high food treatment and a reduced development rate inthe lowfood treatment. The only detectable fitness benefitassociated withcannibalism was a positive correlation betweenthe number of victims consumedand development rate under conditionsof low food availability. On balance,cannibalism appears tobe costly; alternative explanations for its occurrencein thisspecies are discussed.