Inundative release of common green lacewings (Neuroptera: Chrysopidae) to suppress Erythroneura variabilis and E-elegantula (Homoptera: Cicadellidae) in vineyards

The effectiveness of inundative release of common green lacewing, Chrysoperla carnea, (Stephens) to suppress 2 vineyard pests, Erythroneura variabilis Beamer and western grape leafhopper, E. elegantula Osborn, was examined in small-plot and on-farm trials. In 1990, C. carnea larvae were hand-released into quarter-vine cages. Leafhopper densities were significantly reduced by 23.5 and 30.3% in plots that received 29,652 and 88,956 C. carnea larvae per hectare, respectively, as compared with no-release plots. In 1991, C. carnea larvae were hand-released onto vines in uncaged, 3-vine plots; the 2 release rates used closely reflected commercial recommendations. At the lower rate (9,884 larvae per hectare), no significant differences were found between C. carnea-release and no-release plots. At the higher rate (19,768 larvae per hectare), leafhopper densities were significantly reduced by 33.6 and 31.4% in 1st and 2nd leafhopper generations, respectively. In 1992, 3-vine plots were again used and the 3 commercially available lacewing species [C. carnea, Chrysoperla comanche Banks, and Chrysoperla rufilabris (Burmeister)] were tested at a release rate of 19,768 larvae per hectare. The only significant reduction in leafhopper density was in the C. rufilabris-release treatment. From 1990 to 1993, the effectiveness of commercial release programs was tested in on-farm trials using large, replicated C. carnea-release and no-release plots. C. carnea was released at rates between 7,413 and 37,065 eggs per hectare per leafhopper generation. In 9 of 20 trials, leafhopper densities were significantly lower in C. carnea-release than no-release plots. Data from all trials were combined to determine possible explanations for the variation in the effectiveness of C. carnea releases. Possibilities include differences in release trials, rates, and methods, as well as prey density. The average reduction of leafhoppers in C. carnea-release plots, as compared with no-release plots, was 29.5% in cages, 15.5% in 3-vine plots, and 9.6% in commercial vineyards. A significant, although only weakly positive, correlation was found between release rate and effectiveness. There was also a greater reduction of leafhopper nymphs when lacewings were released as larvae, as compared with eggs. Combining data from all studies, the number and percentage of reduction of leafhopper nymphs was related to leafhopper density. Most importantly, when leafhopper densities were above the suggested economic injury level (15-20 nymphs per leaf), the reduction in leafhopper number was frequently not sufficient to lower the leafhopper density below the economic injury threshold.