Evolution of host avoidance in a leafmining fly, Amauromyza flavifrons

Herbivorous insects are characterized by a great diversity of host plant associations, yet, the processes driving host range evolution are not fully understood. When herbivores encounter a novel host, local selection pressures are expected to shape traits that mediate plant-insect interactions. I show that a leafmining fly, Amauromyza flavifrons (Meigen) (Diptera: Agromyzidae), suffers a profound fitness cost by ovipositing on a novel host, Beta vulgaris L. (sugar beet) (Chenopodiaceae). Leafminers from a sugar beet-free population readily oviposit on B. vulgaris leaves, whereas those collected from a population near sugar beet farms discriminate against B. vulgaris. This finding suggests that oviposition specificity in A. flavifrons populations may have evolved in response to the presence of the novel host, and represents the first evidence of host-avoidance evolution in the wild. Because this study compared only one pair of populations and thus lacks replication, future studies will test whether parallel evolution has occurred at B. vulgaris farm locales across North America.