Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2002
Publication Date: N/A
Interpretive Summary: Increased awareness of environmental and safety hazards posed by conventional insecticides has lead to efforts to find safer alternatives for pest control. The photoactive dyes are recognized as one of these potential alternatives, but the effectiveness of these materials is known for only a few insects. We measured the effectiveness of dyes mixed into sugar solutions and fed to adult boll weevils held under a high-pressure sodium lamp. Of the dyes we examined, only rose Bengal and phloxine B consistently killed weevils, and for both dyes weevil death occurred sooner as more dye was consumed. Additional studies of phloxine B showed that more weevils were killed, and death occurred earlier, when the time between consuming the dye and exposure to the light was shortened. Also, feeding on cotton flower buds after eating the dye did not reduce the numbers of weevils that were killed. Our results show that the dyes rose Bengal and phloxine B are effective killing agents for the boll weevil, especially when the weevils are exposed to light soon after eating the dye. These findings should be helpful in efforts to develop alternative control measures for use in environmentally-sensitive areas, or in other situations where use of conventional insecticides is not appropriate.
Technical Abstract: Photoactive dyes are increasingly considered potential alternatives to conventional insecticides. Expansion of eradication programs for the boll weevil, Anthonomus grandis Boheman, has accentuated the need for new toxicants to reduce dependency on organophosphates and minimize environmental impacts. However, toxicity of photoactive dyes to adult weevils has not been thoroughly investigated. We developed methods to assay dye activity against the adult boll weevil, compared the efficacies of selected dyes, and examined the influences of dye elimination on efficacy. Doses of dyes from 0 ? 1.0 ug/weevil were orally delivered in aqueous sucrose and mortality was induced by illumination with a high- pressure sodium lamp. The methods provided consistent mortality responses to rose Bengal and phloxine B, and indicated that mortality occurred earlier as dose increased. In dye comparisons, rose Bengal was the most efficacious followed by phloxine B. Methylele blue, eosin Y, rhodamine B, and erythrosine B failed to consistently produce substantial mortality. Examination of the influences on efficacy of dye elimination by excretion or detoxification indicated that phloxine B was significantly more effective when weevils were exposed to the light source immediately after dye ingestion than when exposure was delayed for 24 or 48 h. Square feeding after dye ingestion did not reduce mortality. Our results indicate the high-pressure sodium lamp provides light of sufficient intensity to permit laboratory examination of photoactive dye toxicity against relatively opaque insects such as the boll weevil, and that both the time-course of mortality and the potential for dye elimination should be considered in interpreting results of dye assays.