The thesis studied the biological control of woolly aphid (Eriosoma lanigerum Hausm.) using European earwig (Forficula auricularia L.) in an Australian apple orchard IPM program. Woolly aphid populations were monitored over the 1995/96 and 1996/97 growing seasons, completing a four year study of the pest's status and management under IPM programs at Bathurst in the Central Tablelands of NSW. Woolly aphid infestation in 2 IPM treatments, based on alternative control techniques for codling moth (Cydia pomonella L.), namely mating disruption and fenoxycarb, were compared with a conventional insecticide azinphos-methyl program. Further, the thesis studied the toxicity, to adult European earwigs, of chemicals commonly used in Australian apple orchards. The pesticide alpha-cypermethrin is highly toxic to weevil spp. and is used by apple growers in Western Australia for their control, but it is also toxic to earwigs. This trial investigated the potential of alpha-cypermethrin to disrupt the biological control of woolly aphid. Following a single application as a butt spray, alpha-cypermethrin suppressed the number of earwigs in apple trees for 14 weeks. The single application did not reduce earwig numbers to the extent that the biological control of woolly aphid was lost, however a full season program with applications every 14 to 21 days to all trees, as recommended to control weevils, within an orchard is likely to be very disruptive. The research also studied the control of woolly aphid using insecticide root-soil drenches. Imidacloprid provided excellent control of woolly aphid for 3 seasons. Pirimcarb provided some suppression of woolly aphid during the first season, but not in subsequent seasons. Chlorpyrifos and vamidothion failed to control woolly aphid in any season. / Doctor of Philosophy (PhD)