Integrated Biological Control of Woolly Apple Aphid in Washington State

Lessando Moreira Gontijo

Woolly apple aphid Eriosoma lanigerum Hausmann is a secondary pest of apples whose outbreaks have occurred more often since about 2000. The increase in outbreaks appears to be associated with changes in pesticide programs and disruption of biological control. Because of the banning of azinphos-methyl and restriction posed on other organophosphates growers are turning more to biological control as an alternative tactic to control woolly apple aphid. This aphid has been documented to have a wide host of natural enemies around the world including syrphids, coccinellids, chrysopids, predatory hemipterans, earwigs and the endoparastioid Aphelinus mali (Haudeman). A survey I conducted in 2008 in central Washington confirmed that syrphids, chrysopids, coccinellids and A. mali are the most common natural enemies of woolly apple aphid occurring in Washington. Conservation of woolly apple aphid natural enemies in the orchard was also studied in 2008, 2010 and 2011. Sweet alyssum Lobularia maritima (L.) Desvaux was the flowering plant that attracted significantly more predatory syrphids into the orchards. A faster response by natural enemies to woolly apple infestation was observed in plots planted with sweet alyssum. In addition, a movement of natural enemies between sweet alyssum and tree canopy was confirmed by an imunomarking technique. Exclusion cage studies conducted in 2010 and 2011 showed that predators together with A. mali can efficiently control woolly apple aphid in orchards under a soft pesticide program. In addition, syrphids did not seem to disrupt parasitism of A. mali, but instead showed an additive effect when combined. The lethal and sublethal effect of orchards pesticides on A. mali were also examined in 2009, 2010 and 2011. Spinetoram, spinosad, carbaryl, organophosphates and neonicotinoids showed a high acute toxicity to A. mali killing more than 90% at full rate. Chlorantraniliprole, lambda-cyhalothrin, novaluron, cyantraniliprole, sulfur, spirotetramat and zinc + manganese hydroxide killed less than 60% of the parasitoids in the acute bioassays at both rates. Only cyantraniliprole, spinetoram and lambda-cyhalothrin showed significant sublethal effects on A. mali. The sublethal effect of cyantraniliprole was due to induction of low fecundity in A. mali, whereas for spinetoram and lambda-cyhalothrin the effect was due to adult A. mali and host mortality. All the studies suggest that biological control of woolly apple aphid has the potential to work in the field. Nevertheless, conservation measures like augmenting alternative food sources for natural enemies and spraying selective pesticides should be adopted.

Integrated Biological Control of Woolly Apple Aphid in Washington State

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