Comparative toxicity of six insecticides on the rhinoceros beetle (Coleoptera: Scarabaeidae)

Abstract

Strategus aloeus (Linnaeus, 1758) (Coleoptera: Scarabaeidae) is a dangerous pest of oil palms in the Americas, because the adults cause several kinds of damage and kill palm trees. Effective methods for pest management are needed urgently. Bioassays were conducted to compare the toxicity to S. aloeus of the insecticides: fipronil, imidacloprid, lambda- cyhalothrin, spinosad, thiacloprid and thiamethoxam. The toxicity of each insecticide to the adults of S. aloeus was determined as: (1) the LC50 and LC90 under laboratory conditions, after exposure of six concentrations of each insecticide applied in a semi-solid diet and used to feed each insect and (2) the mortality under semi-controlled field conditions after applications of insecticides into the beetle galleries in the oil palm tree. The mortality of S. aloeus was higher with fipronil, imidacloprid, lambda-cyhalothrin and thiamethoxam, while spinosad and thiacloprid were less effective. Higher mortalities were obtained with concentrations of 12.5, 25, 50 μL mL-1 for determining LC50 values and 50, 100 μL mL-1 for determining LC90 values during 72 h. The mortalities of S. aloeus had similar tendencies under laboratory and semi-controlled field conditions. Fipronil, imidacloprid, lambdacyhalothrin and thiamethoxam caused substantial mortality in S. aloeus and, thus, can be used rotationally in integrated pest management programs (IPM) against this pest in the oil palm plantations.