Potential of selective insecticides for managing Uraba lugens (Lepidoptera: Nolidae) on Eucalypts

The leaf skeletonizer Uraba lugens Walker (Lepidoptera: Nolidae), an Australian species, locally known as "gumleaf skeletonizer", is well established in New Zealand. This insect has the potential to become a serious pest of forestry and amenity eucalypts (Eucalyptus spp.) and is the focus of a long-term management program. The use of synthetic chemical or biological insecticides is one possible control method within an integrated control program. A series of dose-response trials were conducted using laboratory bioassays to test the efficacy of several insecticides against U. lugens: pyrethroids, spinosad, Bacillus thuringiensis kurstaki Berliner (Btk) and an insect growth regulator, Mimic. Pyrethroids and spinosad proved highly effective against U. lugens larvae, achieving 100% mortality after 3-6-d exposure. The performance of Btk was lower against gregarious skeletonizing larvae compared with solitary chewing larvae. When good coverage of the target foliage is achieved, >90% mortality is possible with Btk. Mimic performed poorly against U. lugens compared with other insecticides tested (<60% mortality). The Eucalyptus species on which larvae were feeding significantly altered insecticide efficacy. Treatments applied to Eucalyptus nitens (Deane & Maiden) Maiden had reduced efficacy compared with E. cinerea F. Muell. ex Benth. or E. fastigata Deane & Maiden. Cooler temperatures also reduced insecticide efficacy, presumably by decreasing movement and food consumption by U. lugens. Recommendations on spray applications to control U. lugens in New Zealand are given.