Breeding Places and Susceptibility Status of Anopheles stephensi Larvae for Temephos in Jaffna, Sri Lanka

Abstract

Anopheles stephensi mosquito is an invasive potential malaria vector in Sri Lanka. Adult Anopheles stephensi shows resistance to many insecticides. Hence, identification of breeding habitats and susceptibility to larvicides are crucial to plan effective vector control programmes. A study was conducted to identify breeding places and to assess susceptibility to temephos larvicide for Anopheles stephensi in Jaffna, Sri Lanka. A study was conducted in Jaffna Medical Officer of Health area including four Grama Niladhari divisions ( J 83, J-84, J-85 & J-86) with high prevalence of Anopheles stephensi. Larval surveys were conducted covering potential breeding places of Anopheles stephensi from September 2021 to September 2022. The results were analysed using Kruskal-Wallis and Mann-Whitney U test. The susceptibility to temephos, was evaluated for Anopheles stephensilarvae using five selected concentrations (0.03125 mg/L, 0.0625 mg/L, 0.125 mg/L, 0.25 mg/L, 0.375 mg/L). Probit analysis was performed to calculate LC99. Three types of places were positive for Anopheles stephensi; wells (94.9%), cement tanks ( 3.8%) and water storage barrels (1.3%) out of 8661 examined. Positivity rate of Anopheles stephensi for wells, cement tanks and water storage barrels were 4.2%, 0.6% and 0.2% respectively. Positivity of Anopheles stephensi in wells were significantly higher than the other breeding habitats (H(3) = 14.74, p = 0.002). LC99 value of temephos for Anopheles stephensi for the tested population was 0.249 mg/L. The predominant breeding place of Anopheles stephensi is Wells. The Anopheles stephensi larvae in Jaffna are susceptible to temephos larvicide. These findings can be used to design appropriate vector control programme to control Anopheles stephensi in Jaffna, Sri Lanka.