The susceptibility of three mosquito species to some commonly used insecticides in three localities in Ashanti Region

The aim of the work was to compare the relative susceptibility shown by the three medically important mosquitoes, (Aedes aegypti, Culex quinquefasciatus and Anopheles gambiae) to four commonly used insecticides. These are Endosulfan (Thiodan) - an organochlorine, λ-cyhalothrin (Karate), - a pyrethroid, Propoxur (Unden 200) - a carbamate, and Chiorpyrifos (Dursban) - an organophosphate. Strains of each of the species were obtained from Fanti Newtown, Akumadan and Kofiase, all localities in the Ashanti region of Ghana and reared in the insectary. Five graded concentrations of the four insecticides in three replicates were tested on the larvae/pupae of the mosquitoes to establish their LC0 and LC100 (Busvine, 1980). Both larvae and pupae of the three species were found to show some resistance to the test insecticides but the degree differed from species to species and also differed according to the insecticide. The LD50 and LD90 were calculated for each insecticide for each species in each locality. Generally the most resistant species to Endosulfan were from Fanti Newtown and the most susceptible species were from Kofiase. For λ-cyhalothrin the most resistant species were from Akumadan, and the most susceptible from, Fanti Newtown. For Propoxur the most resistant species were again from Akumadan and most susceptible were also from Fanti Newtown. Finally for Chiorpyrifos, Fanti Newtown species were the most resistant and the most susceptible were from Akumadan. Within Ae. aegypti strains from the different localities the most resistant strain to all the four insecticides was from Akumadan and least was Kofiase strains. Using the four chemicals against Cx. quinquefasciatus strains, the most resistant strain was from Fanti Newtown and the least resistant was from Kofiase. With An. gambiae, the most resistant strain was from Fanti Newtown and the least resistant strains were Kofiase strains. Across the localities the most effective insecticide was Chiorpyrifos and this was followed by λ-cyhalothrmn, then Propoxur and the least was Endosulfan. Individually, Endosulfan was most effective against Cx. quinquefasciatus species in Fanti Newtown, Akumadan and Kofiase but was least effective against An. gambiae species in all the three localities. λ-cyhalothrin was most effective against Fanti Newtown Ae. aegypti and Fanti Newtown Cx. quinquefasciarus and was least effective in An. gambiae species in all three localities. Propoxur was most effective against all An. gambiae species in all the three localities but least effective against Ae. aegypti species in Fanti Newton, and Cx. quinquefasciatus species from Fanti Newtown and Akumadan and Kofiase localities. Chiorpyrifos was the most effective against Cx. quinquefasciatus from Fanti Newtown and Akumadan as well as An. gambiae species from Kofiase. Chlorpyrifos was least effective against Ae. aegypti species from Fanti and Akumadan and An gambiae species from Fanti Newton and Akumadan as well as Ae. aegypti species from Kofiase. .-cyhalothrin was the most effective insecticide for all Fanti Newton species and Chlorpyrifos for all species in Akumadan and Kofiase. Propoxur was particularly effective against Akumaclan An. gambiae species. In conclusion, Chorpyrifos is the most effective insecticide and because of its advantages like low toxicity to man, easy photodegradation, and effectiveness at much lower concentration, it could be recommended for use in the Ashanti region of Ghana. Though toxic to fish and can contaminate potable water, it can be used with education and caution. λ-cyhalothrin could also be used because of its stability in the sun, and low toxicity to mammals and birds and also effective at low concentrations, but with caution because of its toxicity to pollinators such as honeybees. Propoxur could be recommended for use against Akumadan An. gambiae otherwise it is not effective to the other mosquitoes. However Endosulfan is not recommended for use because of the high resistance against it by almost all the mosquitoes in all the localites. Furthermore, its use must not be encouraged because of its persistence in the environment and its bioaccumulation in tissues of organisms (WHO, 1980).

Source: KNUST