Impact of four insecticides on the European earwig, Forficula auricularia L., in an apple orchard
Abstract:The European earwig Forficula auricularia (Dermaptera: Forficulidae) is an important predator of psyllids and aphids, including the woolly apple aphid. Resurgence of the latter pests is often connected to the use of pesticides which harm earwigs. A field test was carried out in 2008 with four new-generation insecticides (thiacloprid, spinosad, indoxacarb and flonicamid) used in apple production, to study their effects on earwig populations. Earwigs are nocturnal and hide in shelters during the day. We installed bamboo tubes as artificial shelters at the end of May, for sampling purposes. Once the shelters were clearly occupied by earwigs, and when earwigs were in the 4th instar, the insecticides were applied (4 replicates of 7 trees per plot); control plots were left untreated. The numbers of earwigs in the shelters of 5 trees per plot were assessed for up to 10 weeks post-application, by knocking the earwigs out of the tubes, collecting them in a plastic bag and photographing them for later counts from the digital images. Immediately afterwards, the earwigs were released back to the appropriate tree. All of the insecticides caused significant reductions (Henderson & Tilton method) in the earwig numbers as compared with control populations. One week after treatment these were 67% for indoxacarb, 56% for thiacloprid, 52% for spinosad and 40% for flonicamid. Whereas significant population reduction was observed with indoxacarb up to four weeks, effects of the other insecticides decreased much quicker.