Effects of Herbicide Application on Mortality and Dispersive Behavior of the Water Hyacinth Weevils, Neochetina eichhorniae and Neochetina bruchi (Coleoptera: Curculionidae)

Abstract

Toxicities of commonly used water hyacinth herbicides and additives to water hyacinth weevils, Neochetina eichhorniae Warner and N. bruchi Hustache, were tested in the laboratory. Weevils were either sprayed while on water hyacinth plants or dipped directly into the compounds tested. No significant mortality resulted from exposure to 2,4-D, diquat, glyphosate, or additives including a surfactant and a polymer. Exposure to an inverting oil, and its primary component d'limonene, resulted in significant mortality of both species at concentrations tested. Effects of herbicide exposure on flight muscle development seemed to be related to time of year at which exposure occurred. Effects of herbicide application on dispersive behavior were determined by placing marked weevils on artificial weed mats in the field. Mats were subsequently sprayed with a standard concentration of 2,4-D. Weevils consistently migrated from sprayed, dying plants to adjacent healthy, unsprayed plants. Implications for biocontrol strategies of water hyacinth are discussed.