Effective Control of Adult Culex pipiens by Spraying an Attractive Toxic Sugar Bait Solution in the Vegetation Near Larval Habitats

Abstract

This study evaluated the use of an insecticide-treated fruit juice bait against adult Culex pipiens s.l. L. from sewage ponds in Israel. The attractive toxic sugar bait (ATSB) solution (fruit juice, sugar, food dye, oral insecticide spinosad, and BaitStab, a mixture of slow-release substances and preservatives) was sprayed onto 10 Ð15% of the surrounding vegetation of these ponds. The same bait solution, without insecticide, was sprayed onto vegetation at a similar site as a control. Mosquito abundance was monitored in treatment and control sites with six CDC light traps. Mosquitoes in the experimental sites decreased from 125 to approximately eight per trap. Mosquito abundance in the control sites was fairly stable and averaged 60 per trap during the study. Before starting the study parity of mosquitoes from the experimental and control sites averaged 20% multiparous females. After bait/insecticide application, only 3% of the females were multiparous in the treatment area. KEY WORDS mosquitoes, Culex pipiens, fruit juice attractant, oral insecticide, attractive toxic sugar bait It is well known that mosquitoes require sugar from plants for survival, but only a few studies have documented the preference of sugar sources and their relative attraction (Yuval 1992; Foster 1995, 2008). Recent studies have shown that mosquito orientation to particular sugar sources in nature can be used effectively as attractive toxic sugar baits (ATSBs). The potential of manipulating mosquito sugar-feeding behavior as means for control has been overlooked. Recent studies (Mü ller and Schlein 2006, Schlein and Mü ller 2008) showed the potential of using natural, attractive sugar feeding centers for control by spraying them with a solution of sugar and toxin. Ripe fruit also can attract mosquitoes (Joseph 1970) and solutions containing these products were blended with oral toxin and were presented in bait stations (Mü ller et al. 2008). In the current study, we sprayed scattered patches of nonßowering vegetation along a sewage treatment pond with a bait formulation containing fruit juice and a toxin to evaluate its effectiveness against local populations of adult Culex pipiens s.l. L. Materials and Methods Experimental Sites. Experiments were carried out at the end of the dry season, from August to September 2007, near sewage ponds adjacent to the villages Hatzeva and Shezaf in the southern dry region of Israel. The pond in Hatzeva was 20 by 40 m and that of Shezaf was 15 by 30 m. Both were proliÞc larval developmental sites for numerous Cx. pipiens. Around the ponds vegetation dominated by nonßowering reeds Phragmites australis (Cav.) Steud. (Gramineae); Tamarix nilotica trees (Ehrenb.) Bunge (Tamari-caceae); and small thickets of desert vegetation consisting mostly of Artemisia monosperma Delile (Com-positae), Atriplex halimus L., Suaeda asphaltica Boiss. (Chenopodiaceae), Nitaria retusa (Forssk.) Ascher-son (Zygophyllaceae), and Alhagi graecorum Boiss. (Papilinaceae). Together, the vegetation covered 10 Ð15% of the area around each pond. Bait Solution and Application. Bait solution for the experimental site in Hatzeva consisted of 80% juice of overripe to rotting nectarines (Prunus persica variety nectarine; Rosacea), 5% wine (Binyamina dry red wine, Binyamina Winery, Binyamina, Israel), 10% (wt: vol) brown sugar (Nature Sugar brown, Louis Drey-fus, Israel), 0.5% (wt:vol) red food dye (Carmoisine E122, Stern, Natanya, Israel) for marking mosquitoes (Schlein and Pener 1990), 0.04% (wt:vol) of the oral insecticide Spinosad (Tracer, Dow Agrosciences, Cal-gary, AB, Canada), and 5% (wt:vol) of a concentrated mixture of slow-release substances and preservatives (BaitStab; Westham Ltd., Tel Aviv, Israel). The solution was fermented for 48 h, in covered buckets, outdoors in full sun where daily temperatures reached an average of 30C. The same solution prepared without insecticide was used for the control site in Shezaf. The solution was applied using a 7-liter hand sprayer (Killaspray, model 4005, Hozelock-ASL,