Detrimental effects of commonly used insecticides in oil palm to pollinating weevil, elaeidobius kamerunicus faust. (Coleoptera: Curculionidae)

Abstract

Elaeidobius kamerunicus is the main insect pollinator of oil palm in Malaysia. It has improved oil palm pollination, thus leading to a better yield. The lethal concentrations (LC50) of four currently used oil palm commercial insecticides, namely cypermethrin, trichlorfon, fipronil and Bacillus thuringiensis on E. kamerunicus were determined using residual film, topical spray and oral bioassays. The weevil mortality was recorded at 24, 48 and 72 hr after treatment. Probit analysis was used to determine LC50. The result showed that male weevils were more susceptible to trichlorfon and fipronil than female weevils. However, there was no difference between sexes in terms of susceptibility towards cypermethrin. Among the tested insecticides, fipronil had higher lethality on weevil whereas B. thuringiensis was less harmful to weevil mortality by <20% even when treated at the highest concentration (0.26% product). Regardless of the type of insecticides and exposure time, the weevil was less sensitive to the insecticide applied via spray method as compared to oral and residual film. The study findings provide useful information in determining the less harmful insecticides to this pollinating weevils with various mode of actions.