A new pod bioassay method to determine the toxicity of insecticides against Tea mosquito bug, Helopeltis theivora.

Abstract

The insecticide susceptibility of Helopeltis theivora Waterhouse (Hemiptera: Miridae) is being evaluated using shoot and glass-vial assay as described by IRAC. However, the reliability of the assay depends on feeding preference and contact toxicity. Hence, the cocoa pod was used as a substrate to test the susceptibility of H. theivora in comparison with existing methods. The experimental results revealed that the LC₅₀ value of all of the insecticides was relatively lower in the pod bioassay than the other two methods and exhibited maximum mortality within 6 hr of post-exposure. Among insecticides, fipronil was the most effective molecule followed by lambda-cyhalothrin. H. theivora, which prefers to feed on a pod due to more tissue turgidity, thus facilitated adequate sap ingestion; whereas, these were limited in shoot and glass-vial bioassays. Therefore, it could be used as a methodology to determine the susceptibility of H. theivora against a wide range of insecticide molecules.