THE WINDOW OF VULNERABILITY AND ITS EFFECT ON RELATIVE PARASITOID ABUNDANCE

1. The length of time that a gall-forming midge, Rhopalomyia californi ca, was vulnerable to attack by four parasitoid species was measured i n the field at two locations. 2. The midge had a restricted window of vulnerability to each of the parasitoid species, but similar windows o f vulnerability were found at the two sites. 3. A stage-structured mod el was used to illustrate that the length of the vulnerable window sho uld have no effect on the fraction parasitized by a single parasitoid species if that species is the only parasitoid attacking the host in a coupled host-parasitoid interaction. However, the length of the windo w of vulnerability can have a positive effect on the fraction parasiti zed by a species in competition with other parasitoid species. 4. The length of the window of vulnerability can help explain the relative fi eld abundance of four of the common parasitoid species of R.californic a.