Reduction in leafroller (Lepidoptera: Tortricidae) abundance in orchards and vineyards 1976–2016, in Hawke's Bay, New Zealand

Abstract

Abstract Three leafroller species were monitored between 1976 and 2016 by bait and pheromone trapping for adults, larval damage to apples and timed searches on various hosts. Populations of all three species decreased substantially; however, the endemic Planotortrix octo and Ctenopseustis obliquana declined to a much greater extent than did the introduced Epiphyas postvittana. The two endemic species dominated in the 1970s, whereas they are now rarely found on fruit crops. Epiphyas postvittana has now become the principal leafroller species. Leafrollers damaged over 20% of apples receiving no insecticides during the 1980s but, subsequent to 2000, damage has been below 2%. Between 1994–1999 and 2008–2011, the numbers of immature leafrollers in searches on fruit crop and noncrop hosts decreased by 55%. We attribute reduced leafroller populations to increased biological control and changes to insecticide programmes. Several parasitoids were introduced around 1980 and parasitism increased by 19% between 1994–1999 and 2008–2011. Replacing broad‐spectrum insecticides with selective insecticides in the mid‐1990s likely enhanced this trend. Leafrollers were formerly major pests, whereas their status has now changed to being minor pests. Today, they are uncommon on managed and unmanaged fruit crops and noncrop host plants on orchards and vineyards in Hawke's Bay.