Laboratory selection was conducted for fenvalerate resistance in two colonies of the parasitoid, Cotesia plutellae Kurdjumov, each reared on a different colony of its host, Plutella xylostella (L.), with different level of resistance to the insecticide. In the selection regime the insecticide was applied to the host larvae that harbored the parasitoid larvae. Compared with the unselected parasitoid colony, the parasitoid colony selected with the susceptible hosts acquired 4.5-fold resistance after 14 selection cycles, while the colony selected with the more resistant hosts acquired 13.6-fold resistance after 13 selection cycles. These results demonstrate that parasitoid larvae could be exposed to insecticide selection via the hosts, selection with more resistant hosts could accelerate development of resistance in the parasitoid, and resistance genes selected during larval development could be expressed at the adult stage. This information can help improve selection procedures for insecticide resistance in parasitoids. none