The impact of pyriproxyfen on obliquebanded leafroller, Choristoneura rosaceana (Lepidoptera: Tortricidae)
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The obliquebanded leafroller (OBLR), Choristoneura rosaceana (Harris), is one of the most destructive pests of tree fruits in Washington. The development of insecticide resistance in OBLR has led us to explore new management strategies. The use of very low doses of insecticides that have strong sublethal effects represents an environmentally-friendly option to improve existing integrated pest management strategies. We tested the insect growth regulator pyriproxyfen (Esteem® 0.86EC, Valent U.S.A. Corporation) to determine its lethal and sublethal effects on OBLR. A leaf-disk bioassay was used to test seven doses of pyriproxyfen ranging from 0.0 to 3.0 μg per final instar OBLR. Male and female larvae were assessed separately for mortality as well as other parameters of growth and development. We found that response to pyriproxyfen was dose-dependent: only 5-6% of the larvae treated with the highest dose emerged as morphologically normal adults, compared to 86% emergence in the controls. Adult emergence was significantly delayed at doses higher than 0.1 μg per larva. The weights of OBLR pupae and adults were significantly increased whereas fecundity and fertility were significantly reduced at a sublethal dose of 0.03 μg per larva. We conclude that both lethal and sublethal effects contribute to the observed reductions of OBLR densities in tree fruit orchards treated with pyriproxyfen.