Quantification of Dichlorvos Released from Kill Strips Used in Boll Weevil Eradication Programs

Two types of kill strips, Hercon Vaportape II and Plato Insecticide Strip, are used by boll weevil, Anthonomus grandis (Boheman), eradication programs in the United States (U.S.). Both types utilize dichlorvos as the killing agent and are typically replaced in traps on a four-week interval. However, published information on the duration of effectiveness of kill strips is not available and some programs have expressed concern over the duration of their effectiveness in traps. The weekly amounts of dichlorvos released from kill strips were quantified based on the weekly residual dichlorvos content of kill strips aged in pheromone traps up to four weeks. Three trials were conducted between May and November to cover a range of environmental conditions. On average, Hercon kill strips initially contained 61 mg of dichlorvos and released 33.0, 9.4, 5.0, and 2.0 mg of dichlorvos during the first, second, third, and fourth weeks of aging, respectively. Comparatively, Plato kill strips initially contained 93 mg of dichlorvos and released 35.6, 15.3, 9.9, and 7.3 mg of dichlorvos during the respective weeks. Although the quantity of dichlorvos needed to kill boll weevils or to deter predation of captured weevils is not known, our results suggest the effectiveness of kill strips is substantially reduced with each week of aging in traps. As such, reducing the replacement interval of kill strips may be a consideration for optimizing or at least maintaining the benefits of their use in traps.