Checkerspot butterflies in the tribe Melitaeini often co-occur, have similar life histories, and feed on plants with shared secondary chemistry. One might expect these butterflies to share parasitoids that perhaps link their population dynamics. On the other hand, resource partitioning may result in the differentiation of parasitoids among host species, allowing more independent host dynamics. The actual parasitoid communities are made up of species that range from extremely general to those that are species specific. Parasitoids in the genus Cotesia are part of all known checkerspot communities. Rearing records, behavioural experiments and analysis of microsatellite and mitochondrial DNA markers show that Cotesia that use Melitaeini form several clades of cryptic host specific species. I discuss the idea that the cryptic species groups may be explained by resource partitioning, as well as the effect of Cotesia host specificity on the structure of the butterfly-parasitoid community.