Control of Woolly Apple Aphid (Eriosoma lanigerum) by Augmenting Earwigs (Forficula auricularia) in the Canopy of Apple Trees

Woolly apple aphid, Eriosoma lanigerum (Hausmann), is a damaging pest of apple (Malus domestica F.) found in most regions of the world where apples grow. The control of this aphid is becoming increasingly difficult due to changes in pesticide approval in orchards. Forficula auricularia L. is a main predator of E. lanigerum, but the numbers of earwigs in trees are inconsistent and unreliable for the control of the pest. This project aimed to test whether annual additions of earwigs in refugia in the tree canopy would reduce E. lanigerum infestations. In each of three commercial apple orchards with a history of E. lanigerum, we introduced, in the spring of each year, commercial predator refuges containing five earwigs to each tree in six plots (nine trees each) per orchard. The E. lanigerum colonies per plot, aphids per colony and infested leaf nodes were compared with adjacent plots with no added earwigs or refuges. We also assessed the numbers of earwigs in refuges at the end of the growing season. Although in one of the three orchards there was an indication that earwigs placed in refuges in the canopy of apple trees reduced the number of aphid colonies on shoots, this was not statistically significant overall. There were high levels of variation in the numbers of both E. lanigerum and F. auricularia across the three orchards and between years. In general, there were fewer E. lanigerum where there were greater numbers of F. auricularia in trees, but the ability of earwigs to control E. lanigerum following 2 years of introductions was not sufficient alone. Forficula auricularia's contribution to the control of other important orchard pests must not be overlooked. Future research should include identifying the causes of the low and inconsistent earwig numbers in apple orchards.