Prey preference of a wasp determined by nest size supports the role of natural selection in body size evolution in Cassidinae leaf beetles

The prey preference of a predator can impose natural selection on prey phenotypes, including body size. Despite evidence that large body size protects against predation in insects, the determinants of body size variation in Cassidinae leaf beetles are not well understood. We examined the prey preference of the digger wasp Cerceris albofasciata, a specialist predator of adult Cassidinae leaf beetles, and found evidence for natural selection on prey body size. The wasp hunted prey smaller than the size of their nest entrance. However, the wasp preferred larger prey species among those that could be carried into their nest. Thus, the benefits of large prey and the cost associated with nest expansion might determine the prey size preference. As expected from the prey species preference, the wasp preferred small individuals of the largest prey species, Thlaspida birarnosa, and large individuals of the smallest prey species, Cassida piperata, resulting in natural selection on body sizes. In intermediate-sized prey species, however, there was no evidence for selection on body size. Natural selection on body size might explain the variation of prey morphologies that increase body size, such as explanate margins, in this group.

Automated summary

The predator digger wasp Cerceris albofasciata showed prey size preference and natural selection on body sizes when hunting adult Cassidinae leaf beetles, preferring larger prey that could be carried into their nest but hunting smaller prey than their nest entrance size. This suggests that the benefits of large prey and the costs associated with nest expansion influence prey size preference in this predator-prey system.