Biological control of woolly apple aphid, Eriosoma lanigerum (Hausmann), during transition to integrated fruit production for pipfruit in Central Otago, New Zealand

Abstract

Woolly apple aphid (WAA), Eriosoma lanigerum (Hausmann), and its natural enemies were monitored from 1994 to 2000 on apples at Clyde, Central Otago, New Zealand during the transition from conventional fruit production (CFP), which used broad spectrum insecticides, to integrated fruit production (IFP), which was based on selective insecticides. Populations were compared in orchard blocks under three management regimes: CFP; transition to IFP; and a biological fruit production (BFP) programme which complied with BioGro® organic certification. WAA remained at very low levels in the CFP programme, because of insecticides, and in the BFP programme, primarily because of natural enemies. Transition to IFP was accompanied by a surge in WAA and a slow colonization by natural enemies which took at least four years to reduce the aphid population to acceptable levels. The principal natural enemy that achieved this was the parasitoid Aphelinus mali (Haldemann), assisted by predators whose contribution remained obscure, including the brown lacewing Micromus tasmaniae (Walker) and the European earwig Forficula auricularia L. A single annual application of lufenuron within the IFP programme was not detrimental to any of these natural enemies, although further research is needed to confirm its lack of impact on the lacewing. Lufenuron reduced arboreal predator diversity, as measured by the Shannon-Wiener index, and this was in part due to decline in the populations of the generalist predator Orius vicinus (Ribaut) and the coccinellid mite predator Stethorus bifidus Kapur. Pirimicarb was an effective selective aphicide for integration with the action of the natural enemies of WAA, but a substitute is required, as its use is no longer permitted on export crops. The implications of these findings for the management of WAA in IFP are discussed.