Who ate all my leafrollers?

Abstract

Leafrollers are pests of many fruit crops, and insecticides are used to control their numbers in commercial orchards. However, little is known about how much their natural enemies contribute to their control. Over two summers, larvae of two leafroller species were established in leaf rolls on potted poplar plants, which were placed along shelterbelts in 16 kiwifruit orchards. After a minimum of 38 hours, the leafrollers were retrieved and reared to determine parasitism rates and parasitoid identities. Egg batches and tethered larvae were also placed in the shelterbelts, with some monitored by video cameras, to determine predation rates and predator identities. Up to 3% of larvae in leaf rolls were parasitised in some orchards, by four different parasitoids, with the fly Trigonospila brevifacies accounting for the majority. Rates of predation were higher, with up to 40% of eggs, and 37.2% of larvae being taken. Fourteen different predator taxa were observed feeding on eggs and larvae, with the mite Anystis baccarum, earwigs, and spiders being the primary predators. Understanding which natural enemies are suppressing leafroller populations offers the potential for conserving or increasing those predator and/ or parasitoid numbers in cropping environments.