Responses of mealy plum aphids (Hyalopterus pruni), leaf-curl plum aphids (Brachycaudus helichrysi), and their natural enemies to various ratios of aphid sex pheromone components in prune orchards

Mealy plum aphids, Hyalopterus pruni (Geoffroy), and leaf-curl plum aphids, Brachycaudus helichrysi (Kaltenbach), are the primary arthropod pests in California’s dried plum (i.e., ‘prune’) crop. The sexual stage of the life cycle occurs in prune orchards in the fall, during which time males respond to sex pheromones produced by oviparous females. The sex pheromones produced by oviparous mealy plum aphids (MPA) and leaf-curl plum aphids (LCPA) are species-specific blends of two chemicals, (4aS, 7S, 7aR)-nepetalactone and (1R, 4aS, 7S, 7aR)-nepetalactol. In order to assess the potential use of aphid sex pheromones for monitoring and management of MPA and LCPA, experiments were conducted in prune orchards located in the main prune-producing region of the United States, California’s Sacramento Valley region to determine the attraction of MPA and LCPA to different ratios of the two sex pheromone components. Additionally, a number of natural enemies have been shown to use host-produced sex pheromones as kairomones to facilitate host location, predation, and parasitism. Therefore, we also evaluated the attraction of key predators in the system, green lacewings, and aphid parasitoids to the different nepetalactone and nepetalactol ratios. The following neptalactone:nepetalactol ratios were included in the experiment: 1:0, 0:1, 1:1, 2.6:1, 3.4:1, 5:1, 7:1, and 0:0 (no-pheromone control). The numbers of MPA, LCPA, green lacewing adults, and aphid parasitoids in each trap were quantified weekly throughout the fall aphid migration and mating season and compared among treatments. The results of this study will be presented and biological and management implications discussed.