Technical Abstract: In 2001 and 2002, we monitored densities of grape leafhopper (Erythroneura elegantula Osborn and E. ziczac Walsh) eggs from June through September in managed and non-managed vineyards in Washington State. Anagrus parasitoids (Hymenoptera: Mymaridae) were reared from sampled parasitized leafhopper eggs. Densities of non-parasitized and parasitized E. elegantula eggs, and non-parasitized E. ziczac eggs, were significantly higher in non-managed grapevines, although this pattern was not consistent for the latter two groups. Densities of parasitized E. ziczac eggs were consistently low across management regimes. Anagrus erythroneurae, A. daanei, and A. tretiakovae emerged from parasitized E. elegantula eggs, while the latter two mymarid species also parasitized E. ziczac eggs. Of these species, A. tretiakovae was the most common parasitoid of Erythroneura leafhopper eggs within sampled vineyards. From 2001-2003, we used yellow sticky traps to collect Anagrus wasps and potential leafhopper hosts from blackberry, grape, and wild rose sites, because these habitats might serve as refugia for the wasps. All three Anagrus species collected within vineyards and a fourth species, A. atomus, were found on traps in these plant habitats. Several leafhopper taxa that could serve as potential alternative hosts for Anagrus spp. were also collected. Our collection of A. daanei, A. tretiakovae, and A. atomus in Washington represent range extensions for these species, revealing several novel candidate species for conservation. Because we consistently found Anagrus species of agricultural importance within rose and blackberry patches, cultivation of these plants close to vineyards may enhance colonization by Anagrus and thus improve grape leafhopper biocontrol.