Augmentative Releases of Aphytis melinus (Hymenoptera: Aphelinidae) To Suppress California Red Scale (Homoptera: Diaspididae) in Southern California Lemon Orchards

Abstract

Releases of Aphytis melinus DeBach, timed in the spring to coincide with the presence of virgin adult female California red scale, Aonidiella aurantii (Maskell), reduced the percentage of infested fruits at season’s end in two sets of southern California lemon orchards when compared with those in nonrelease orchards. The percentage of infested fruit, however, did not differ with the level of release (i.e., 49,420, 98,840, 197,680 per hectare). Aphytis releases did not reduce scale densities on twigs or the number of male scales caught in traps baited with California red scale pheromone. These results are consistent with the known preference by Aphytis for the larger female scales that occur on leaves and fruits over the smaller male and female scales on twigs and branches. Male scales are attacked less frequently than female scales because male scales are much smaller. This preference for the larger female scales probably explains the similarity in the number of males trapped among treatments. Releases of A. melinus in late winter and the spring, when the virgin female scales are most abundant, are an effective tactic for controlling California red scale on fruit in southern California and one that is economically competitive with traditional pesticide treatments but without disruptive side effects.