In-Field Evaluation of Drone-Released Lacewings for Aphid Control in California Organic Lettuce

Aphids are one of the most economically important pests to California's Central Coast lettuce industry. Aphids vector the lettuce mosaic virus and are crop contaminants in the packaging of the product. Lettuce aphid, Nasonovia ribisnigri (Mosley) (Hemiptera: Aphididae), is one of the predominant aphid species in lettuce, and it poses unique management challenges forming colonies inside the lettuce head. Current management practices rely on repeated foliar insecticide applications to reduce aphid densities per plant. Some organic growers have explored the release of laboratory-reared beneficial insects to manage aphids in their commercial fields. This project sought to document the effects of drone-released lacewing eggs on lettuce aphid densities in organic romaine lettuce fields. Commercially reared lacewing eggs were released at a rate of 74,131 eggs/ha and organic-certified insecticides were sprayed following their respective label recommendations. Our results could be interpreted as preliminary evidence that drone release of lacewings could reduce aphid densities (15.6-150.0 aphids/lettuce head) when compared to the untreated plots (32.1-257.9 aphids/lettuce head). Aphid densities were also decreased after the application of foliar organic-certified insecticides (11.77-143.5). Traditionally, the cost of labor has limited the use of beneficials in the lettuce production system, but the use of drones for these releases may make this strategy more attractive. Based on our calculations, spraying an organic-certified insecticide is less expensive (direct operational costs of U.S. $ 116.36/ha) than releasing beneficial insects by hand ($ 185.40) or by drone ($ 176.00) when mimicking the conditions of this study.