Fitness consequences of egg cannibalism in the Colorado potato beetle, Leptinotarsa decemlineata

Cannibalism is an extreme form of competition that provides a nutritional benefit for the cannibal while completely removing the competitor. In the Colorado potato beetle, Leptinotarsa decemlineata, neonates commonly consume unhatched sibling eggs and appear unable to discriminate based on relatedness, adding inclusive fitness costs that must be balanced by these benefits. In a study to measure direct fitness benefits of cannibalism, I provided neonates with either eggs and foliage or foliage alone from plants that were either untreated or treated with the pesticide imidacloprid. Larval mass and developmental stage were then measured daily into adulthood, along with emerging adult mass and female fecundity. To determine whether cannibalism has evolved with a host-plant shift, I conducted a three-year field study to compare neonate cannibalism rates from populations on a patchily-distributed native host (buffalobur, Solanum rostratum) in their native range Mexico and those on an adopted agricultural host (potato, Solanum tuberosum) in their introduced range in the U.S. Finally, I examined whether females mediate cannibalism by plastically responding to environmental conditions to alter their offspring’s opportunity to cannibalize. Well-fed, singly-mated females were provided with either high- or low-quality plants for ovipositing, and clutch size, hatching asynchrony, and the proportion of unviable eggs were measured. I present the final results of these studies and a discussion of the overall fitness consequences of egg cannibalism by neonates in this species.