Aphelopus albopictus Ashmead (= A. comesi Fenton), a dryinid nymphal-adult parasite, has been reported as a major mortality agent for grape leafhopper, Erythroneura elegantula Osborn, in the San Joaquin Valley of California. Parasitism levels varied widely among different vineyards. Our studies report up to 33% parasitism of adult grape leafhoppers, with levels considerably less during much of the season.

In comparing the efficiency of the D-Vac and yellow sticky cards for monitoring the abundance of A. albopictus, parasitized grape leafhopper adults, parasitized variegated leafhopper adults, and nonparasitized adults of both leafhopper species, it appears that sticky yellow cards are less efficient at capturing A. albopictus parasitized grape leafhopper adults than adults of either leafhopper. The two sampling methods did not correlate well for adult A. albopictus. The within-vine distribution of A. albopictus was consistent with that reported in the literature for the nymphal stages of the variegated leafhopper, with the majority recorded in the more shaded areas within the canopy of the distal third of the canes. However, grape leafhopper and variegated leafhopper adults were not captured in greater frequency on shaded leaves.

The variegated leafhopper, which was abundant at one of the study sites, is rarely parasitized by A. albopictus. Chemical intervention for control of this pest will likely increase, resulting in disruption of the normally high level of biological control directed against the grape leafhopper.