Bionomics and control effects of anopheles stephensi in Mannar and Jaffna districts of Sri Lanka

Abstract

BACKGROUND: Sri Lanka was declared as a country that eliminated malaria disease in 2016 by the World Health Organization. Recent report of Anopheles stephensi as an invasive vector in the northern part of Sri Lanka is one of the challenges to maintain themalaria free states in the country. METHODS: Entomological surveys were conducted at three selected localities in Jaffna and Mannar Districts of Sri Lanka from January 2019 to January 2020 using three entomological techniques. Detailed biology and life cycle related information namely were assessed. Further, effectiveness of insecticide based control efforts (novaluron andtemephos) and application of larvivorous fish Poecilia reticulata were evaluated under laboratory set-up. The Vectorial Capacity (VC) was calculated using a mathematical-based approach. RESULTS: According to the egg morphology, Mysorensis biotype (47%) was the predominant followed by type (38.1%) and intermediate (14.9%). The mating success was 80.7 + 4.45%. The mean hatching period was 1.9 + 0.03 days, with a hatching rate of 86.2 + 0.77%. Overall, 8.0 + 0.14 days were irequired for larval development and 30.3 + 0.14 h were spent in \4e pupal stage. The pupation success was 94.5 + 0.37%, and the majority were males (53.1 + 0.73%). The mean fecundity was 106.5 + 6.38 eggs and a gonotrophic cycle of 3.4 + 0.06 days. The female survival rate was 43.2 + 2.4%, with a mean biting frequency of 66.6 + 3.5%. The average VC of adult An. stephensi was estimated to be 18.7. Significant variations in adult emergence were observed from both larval stages at different salinity levels (P < 0.05). The lowest survival rate was reported as 15.8 2.47% at 25 ppt. The highest mortality rate (100%) at a 1-hour exposure period was observed from temephos at >100 ppm. The nortality rates varied significantly for different concentrations and larvicides (P < 0.05). At 24-h of the exposure period, the 100% mortality of An. stephensi larvae were observed from Bi h temephos and novaluron even at 0.04 ppm. In larvivorous fish study, the survival rate of P. reticulata in both Jaffna and Mannar Districts was significantly different at different chlorine levels (P80% even at 0.75 mg/L. At the 24-hours, the mean survival rates of 70.0+ 5.8% (Jaffna) and 81.7 + 4(Mannar) were observed at 0.75 mg/L. At 48 hours, the fish survived only at 0.75 mg/Lindicating a higher survival rate from Mannar (81.7 + 4.4%), while the fish from Jaffna denoted 70.0 + 5.8% of survival. CONCLUSIONS: The type biotype, which: is an effective vector in the Indian subcontinent is present in Sri Lanka. Anopheles stephensi indicated a vectorial capacity of over 18. There is a high potential of increasing density of An. stephensi in coastal ecosystems. The temephos and novaluron can be recommended as effective larvicides for chemical-based control of An. stephensi in Jaffna, Sri Lanka. The fish captured from Mannar demonstrated a higher tolerance to chlorine levels.