Insecticide Use Pattern, Residues in Soil and Water and KJDR Resistance in Anopheles Gambiae S.L. on Rice Farms in Okyereko,Central Region

Abstract

Indiscriminate use of insecticides in controlling insect pests of agricultural crops has been implicated in the development of resistance in disease vectors such as the Anopheles gambiae s.l Giles (Diptera: Culicidae) populations that breed within farming areas. Since vector control strategies are insecticide based, it is important to study insecticide resistance in farming areas such as irrigation sites where vectors are breeding. The aim of the study was to investigate insecticide use pattern among rice farmers in Okyereko, Central Region of Ghana, determine residues level in soil and water samples from mosquito breeding grounds and to study kdr resistance in An. gambiae populations on rice farms in the area. A questionnaire based survey was used to investigate the pattern followed in the use of insecticides. The survey results showed that farmers were using only pyrethroids (permethrin and lamdacyhalothrin) against stemborers and caseworms which are the key rice pests in the area. The general pattern of using insecticide is plagued with many problems due to lack of adequate knowledge and inappropriate equipments for proper insecticide use. Insecticide residues level in soil and water samples were determined using gas chromatograpy-mass spectrometry. Varying levels of lamdacyhalothrin, permethrin and cypermethrin were detected in both soil and water samples suggesting that these environments were contaminated with these insecticides. Susceptibility status of An. gambiae s.l to malathion propoxur, DDT, permethrin and deltamethrin was determined using WHO bioassay test kit. The population was found to be susceptible to malathion and propoxur but resistant to DDT, permethrin and deltamethrin. High knockdown times were recorded for the wild population relative to the susceptible strain. Molecular studies revealed that An. gambiae s.s was the dominant species in the area and its M form was found to be more prevalent as all tested individuals were discovered to be An. gambiae s.s M form. Kdr mutation gene was detected in all tested An. gambiae s.s individuals suggesting that kdr mutation is one of the main resistance mechanisms employed by Anopheles mosquitoes in the area. The indiscriminate use of insecticides in the area, the residue levels in soil and water samples from breeding grounds, the resistance ratios and the high presence of kdr gene is suggestive that, the probable misuse of insecticides in agriculture is strongly contributing to the development of resistance in Anopheles mosquitoes breeding in the area.