The increased use of thiamethoxam seed treatments for controlling pests such as the bean leaf beetle, Cerotoma trifurcata (Forster) (Coleoptera: Chrysomelidae), suggests the need for methods to measure and monitor the development of resistance to thiamethoxam. The objectives of this study were to develop a bioassay method that can be used to monitor bean leaf beetle susceptibility to thiamethoxam, and to quantify the relative concentrations of thiamethoxam and clothianidin in early growth stage soybean tissue treated with thiamethoxam as a seed treatment. Overwintered and F1 bean leaf beetles were collected from alfalfa and soybean fields and used in excised soybean leaf laboratory bioassays to measure susceptibility to thiamethoxam. Petioles of excised leaves were immersed in 0, 10, 50, 100, 500 and 1000 ng a.i./ml thiamethoxam solutions, beetles were placed on the leaves, and beetle mortality and defoliation levels were recorded. The bioassay method proved adequate to calculate an LC50 and LC90, and an EC50 based on defoliation level. The quantification of insecticide residues in soybean leaves from different vegetative stages indicates that the thiamethoxam concentration declines rapidly as the plant grows, and concentrations are at lethal levels for bean leaf beetles through V2. These results provide a method for monitoring bean leaf beetle susceptibility to thiamethoxam that is more representative of the pathway of exposure encountered by beetles in the field, particularly with respect to seed treatments, and provides an estimate of baseline susceptibility for future thiamethoxam resistance monitoring efforts.
You have requested a machine translation of selected content from our databases. This functionality is provided solely for your convenience and is in no way intended to replace human translation. Neither BioOne nor the owners and publishers of the content make, and they explicitly disclaim, any express or implied representations or warranties of any kind, including, without limitation, representations and warranties as to the functionality of the translation feature or the accuracy or completeness of the translations.
Translations are not retained in our system. Your use of this feature and the translations is subject to all use restrictions contained in the Terms and Conditions of Use of the BioOne website.