Optimizing biological control of mealybugs with lacewing larvae

Abstract: The citrus mealybug Planococcus citri (Risso) is a major pest species in ornamental crops in greenhouses. The decreased use of broad-spectrum pesticides seems to be related to an increase of mealybug infested greenhouses. Biological control with specific parasitoids and predatory beetles is not always effective and often considered as too expensive. In this study we explored the possibilities to use lacewing larvae for controlling mealybugs in ornamental greenhouse crops. We compared two species of the carnea-group of Chrysoperla green lacewings: Chrysoperla lucasina (Lacroix) and the commercial species Chrysoperla carnea s.str. (Stephens). Larvae of C. carnea s. str. were not able to complete their larval development when feeding exclusively on mealybugs, whereas half of the larvae of C. lucasina developed successfully until the pupal stage. Moreover, second instar larvae of C. lucasina consumed significantly more mealybug larvae than C. carnea s. str., suggesting that C. lucasina is more suitable for mealybug control. We further tested whether alternative prey or food source affects the control of the citrus mealybug by larvae of C. lucasina. Sterilized eggs of Ephestia kuehniella Zeller appeared to be an excellent food source for larvae of C. lucasina as shown by the fast developmental time and low mortality of larvae when feeding on this prey. The addition of the prey mite Acarus siro (L.) seemed to supplement the diet of mealybugs, resulting in an increased larval developmental rate of C. lucasina. A greenhouse trial showed a slightly better mealybug control by lacewing larvae with supplemental prey mites. However, adding Ephestia eggs as a superior food distracted the lacewings from their target prey, thereby reducing the control of mealybugs.