Colonization and Temephos (Abate) insecticide susceptibility status of Aedes aegypti mosquitoes from selected townships in Yangon Region

Aedes mosquitoes are primary vectors for dengue fever, dengue hemorrhagic fever, yellow fever, chikungunya, and Zika virus. Temephos, a widely used larvicide in Myanmar, has been employed for dengue vector control for over a decade. Thus, it is important to assess the larvicide susceptibility status of Aedes mosquitoes, particularly Aedes aegypti, which is dominant in Yangon Region. Establishing dengue vector colonies in an insectary is crucial for larvicide susceptibility experiments and also for vector competence study. Aedes aegypti larval collection activities were conducted in five townships of Yangon Region (Insein, Shwe Pyi Thar, Dagon, North Dagon, and South Dagon) from September 2023 to August 2024 to establish a laboratory colony. The temephos larvicide susceptibility status of laboratory-reared F1 generations of third and fourth instar Aedes larvae was tested using laboratory doses of 0.1 g/L and field doses of 1 g/L temephos. Egg-laying ability, hatching ability, and production of offspring were also recorded. Results revealed that 74%, 84%, 97.5%, 97.5%, and 100% mortality was observed within one hour of exposure to the laboratory dose from Dagon, Insein, North Dagon, Shwe Pyi Thar, and South Dagon townships, respectively. However, all F1 generation Aedes aegypti larvae exhibited 100% mortality within 24 hours when exposed to both laboratory and field doses of temephos. Meanwhile, the notable high mean for egg-laying was observed in the F2 generation (76.77 ± 23.14 eggs, range: 40-105) and the F3 generation (74.95 ± 23.14 eggs, range: 60-101). The F2 generation also exhibited the highest egg hatching ability (73.29 ± 6.3%). In all generations, the emergence of female pupae was higher than that of male pupae. Field dose of temephos remains effective against Aedes aegypti larvae within 1 and 24 hours, although some tolerance to laboratory doses was observed within one hour. Based on these results, it can be concluded that the test larvae from all areas remain susceptible to temephos. The high egg-laying capacity of F2 and F3 generations, coupled with the higher emergence of females, poses a potential risk for dengue transmission. Therefore, temephos can still be used as a larvicide, particularly for controlling Aedes aegypti larvae.