Release Strategies Affect Survival and Distribution of Green Lacewings (Neuroptera: Chrysopidae) in Augmentation Programs

Abstract

We evaluated 3 aspects of release strategies used to augment green lacewings ( Chrysoperla spp.): the delivery system, the release rate and timing, and the lacewing developmental stage released. Tests were conducted in vineyards with either the common green lacewing, Chrysoperla carnea (Stephens); the Comanche lacewing, Chrysoperla comanche Banks; or Chrysoperla rufilabris (Burmeister). Lacewings were released to suppress 2 leafhopper pests, Erythroneura variabilis Beamer and the western grape leafhopper, Erythroneura elegantula Osborn. Two commercial delivery systems were compared. In the 1st delivery system, a mixture of lacewing eggs and com grit was placed in paper cups, which were distributed to every 5th vine in every other row. This delivery system resulted in poor egg hatch and larval dispersal. Egg hatch was low (≈60%) in the paper cups, compared with egg hatch when lacewings were reared in individual cells (≈91%). The poor egg hatch is attributed primarily to cannibalism. Larval dispersal from paper cups with com grit was 25% lower than that from cups without com grit, resulting in incomplete distribution of lacewings throughout the vineyard. In a 2nd delivery system, lacewing eggs, combined with com grit, were dropped onto the vines from a moving flatbed trailer. Egg hatch was ≈62%. Eggs were delivered to each vine and vine row, although delivery of eggs was uneven. More eggs were dropped at the beginning (≈11 eggs per vine) of each release batch than at the end (≈5 eggs per vine). Using a noncommercial delivery system, release rates between 6,175 and 1,235,000 eggs or larvae per hectare were tested. No correlation between release rate and prey density was found. Releases timed to ≈50–70% leafhopper egg hatch had a greater effect on leafhopper densities than releases timed to peak leafhopper nymph densities. In the 3rd experiment, we tested the effectiveness of egg versus larval releases. In egg release plots, there was ≈70% egg mortality and leafhopper densities were not significantly different from no-release plots. In larval release plots, ≈50% of the larvae survived until the 3rd instar and there was a significant reduction in leafhopper densities.