Proc. Natl Acad. Sci. USA doi:10.1079/pnas.0904695106 (2009)

Does sex promote pest resistance? Marc Johnson of North Carolina State University in Raleigh and his team tested the susceptibility of 32 species of evening primrose (Onagraceae) to a selection of herbivores. This plant group contains both sexually reproducing species and functionally asexual species.

In the lab, the researchers found that generalist caterpillars, which eat a variety of plants, ate 32% more leaf tissue on asexual than on sexual plants. And in a field experiment, generalist herbivores consumed 64% more leaf tissue on asexual species. However, reduced sexual reproduction seemed to help protect against specialist herbivores.

This, the researchers say, supports the previously untested 'recombination-mating system hypothesis', which holds that sexually reproducing species should have greater resistance to arthropod herbivores.