Efficacy of five Insecticides against Oribius Inimicus Marshall and O. Destructor Marshall (Coleotera: Curculionidae)

Abstract

Onbius inimicus and 0. destructor are serious horticultural pests of the Highlands region of Papua New Guinea. Adult weevils feed externally on all non-woody parts of a wide range of agricultural and amenity plants. No insecticides currently registered for use in PNG have been formally tested against these insects. In this study we used laboratory bioassays to evaluate the efficacy of five insecticides (Karate® [Lambda-cyhalothrin], Malathion, Chlopyrifos, Target® [Primiphos-Methyl Permethrin] and Orthene® [Acephate]), all of which are commercially available and commonly used by Highlands' farmers. Follow-up laboratory and field trials of the two most promising chemicals tested efficacy at one-quarter, one-half and 1 x manufacturers' label dilution rates. Of the insecticides tested, Karate®, Target® and Chlophyrifos were found to be the most effective in terms of both total knockdown and time to knockdown. In laboratory bioassays, 10(1% mortality was reached within 20 minutes for these chemicals when insecticide was applied topically to individuals. In field studies, plots treated with Karate® yielded a sigmficantly greater weight and number of fruit than plot treated with Target®, but different dosage
rates (one-quarter, one-half or full manufacturers' recommended concentrations) within insecticide type did not alter yield. We recommend Karate® as the chemical of preference for Highlands' growers for Oribius control because of its significantly lower cost and better field control.