EFFECT OF NATIVE NATURAL ENEMIES AND AUGMENTATIVE RELEASES OF CHRYSOPERLA-RUFILABRIS BURMEISTER AND APHIDOLETES-APHIDIMYZA (RONDANI) ON THE POPULATION-DYNAMICS OF THE GREEN APPLE APHID, APHIS-POMI DEGEER

The impact of native natural enemies, supplemented by augmentative releases of the green lacewing, Chrysoperla rufilabris Burmeister (Neuroptera: Chrysopidae), and/or the cecidomyiid, Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae), on the population dynamics of the green apple aphid, Aphis pomi De Geer (Homoptera: Aphididae), was assessed in a series of experiments conducted in north central Washington State, USA. In one trial, C. rufilabris alone was released at a rate of 200 eggs or first instar larvae per tree per week for 6 weeks; in a second experiment, it was released in combination with A. aphidimyza at rates of 400 eggs and 250 pupae respectively per tree per week. In a final trial, A. aphidimyza alone was released at a rate of 200 pupae per tree per week for the duration of the growing season. The dominant native natural enemies in the study area were Chrysopa nigricornis Burmeister, A. aphidimyza, Orius sp. (Hemiptera: Anthocoridae), and various species of Syrphidae, Chamaemyiidae, and Coccinellidae (principally Coccinella transversoguttata Faldermann and Hippodamia convergens Guerin). Exclusion cage techniques indicated that this native natural enemy complex caused significant mortality of A. pomi However, no effect of the augmentative release treatments could be demonstrated, and where plant growth was vigorous and aphid populations high, the numerical response of indigenous generalist predators was insufficient to keep A. pomi densities below damaging levels.