Investigation of the Grape Mealybug Complex and its Natural Enemies to Improve Biological Control

Vineyard blocks in which we released Pseudaphycus angelicus, an important grape mealybug parasitoid, in 2000 were monitored in the 2001 season. In the Tulare County table grape block, lowered levels of mealybug damage and elevated levels of parasitism (compared to 2000) were found throughout the release and control plots, suggesting that overwintered parasitoid had moved from the initial release location. Releases planned for the 2001 season were less successful because of low insectary production of P. angelicus. Mid-season releases with a small number of parasitoids did not show any affect on mealybug density or damage ratings. Similarly, releases of green lacewing eggs did not show a reduction of mealybugs or economic damage. Studies testing alternative bait-control for the Argentine ant were tested. A 25%sugar solution and small amounts (0.001-0.0001%) of either imidacloprid, fipronil or thiomethoxam were placed in bait traps throughout a heavily infested Napa Valley wine grape vineyard. Results show a significant late-season reduction of ant activity at the fipronil and thiomethoxam treatments. However, there was no reduction in mealybug density or increase in parasitoid activity. While results showed no economic reduction of Argentine ants, we are encouraged by new information gained and will make the needed adjustments for study in the 2002 season. Finally, we tested the effect of nitrogen fertilization (0, 25, 50, 100, 200 and 400 lbs/ac) and girdling and gibberellic acid practices on mealybug populations. Results from field trials showed no difference between N fertilization treatments or berry sizing practices in mealybug density or egg deposition. We believe these field results were influenced by resident natural enemies, which lowered mealybug densities. In controlled greenhouse trials, mealybug densities and egg deposition on potted plants were greater in higher N fertilization treatments. We conclude that more vigorously growing vines can increase mealybug pest status. There is less evidence that berry-sizing practices have any influence on mealybug pest densities.

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