INSECTICIDE RESISTANCE PROFILE OF AEDES AEGYPTI (DIPTERA: CULICIDAE) AGAINST PYRETHROIDS IN DENGUE-ENDEMIC AREAS OF DISTRICT SWAT, PAKISTAN

• Fawad Khan

  Department of Entomology, Abdul Wali Khan University Mardan & Health Department, Swat, Khyber Pakhtunkhwa,

  Author

• Gul Zamin khan

  Nuclear Institute for Food and Agriculture, Peshawar

  Author

• Brekhna Faheem

  Department of Zoology, Abdul Wali Khan University Mardan.

  Author

• Muhammad Tariq Khan

  Department of plant protection Ministry of national food security & Research Karachi Pakistan

  Author

• Farman Ali

  Department of Entomology, Abdul Wali Khan University Mardan

  Author

Aedes aegypti is the most important vectors of dengue virus, which is becoming more of a threat to the effectiveness of vectors management programmes due to the mosquito’s resistance to insecticides. Another aspect that has been maintained is the use of Pyrethroid insecticides in Pakistan to control dengue with no history of insecticide resistance in the northern part of the country, such as District swat. The objective of the present study was to determine the efficacy and resistance of the popular pyrethroid insecticides applied to control field populations of Ae. aegypti in District Swat, Pakistan. The research in question conducted six area surveys within the period from April to October 2024 in Tehsil Kabal, District Swat. The Ae. aegypti third instar larvae were placed under laboratory conditions by collecting them from various breeding sites and exposing them to specific conditions. The experiments conducted consisted of larvicidal bioassays with four pyrethroid insecticides: cypermethrin, deltamethrin, alphacypermethrin and lambda-cyhalothrin as recommended by the World Health Organization. Mortality was assessed initially at 24 and 48-hour time-period, but the 48-hour time period was ultimately disregarded due to differences in solubility observed in early experiments and the impracticality of field application. Probit analysis was used to estimate the lethal concentration (LC₅₀) and resistance ratios (RR) between the isolates and a laboratory-reared susceptible isolate of Rockefeller. The status of resistance was established using the WHO thresholds (susceptible: RR<5; moderate resistance: RR 5-10; high resistance: RR>10). Six sets of fields (7, 200 larvae and 3 replicas) of each concentration were tested by the experimenters. The range of control mortality confirmed all bioassays to be in the range of 0-4.3% (mean value 1.8±0.6%). The insecticides and collection sites showed marked differences with regard to mortality. Cypermethrin and alphacypermethrin stood out for high, even extreme, resistance. Their LC₅₀ values were high—between about 122 and 265 µg/ml for cypermethrin and 130 to 228 µg/ml for alphacypermethrin—with resistance ratios over 10 in most sites. Deltamethrin was a mixed bag: in some places, mosquitoes were still mostly susceptible (RR just over 1), but in others, resistance crept higher (up to 4.75). So deltamethrin is only partly reliable, depending on where you look. Lambda-cyhalothrin generally worked best and killed the most mosquitoes at most sites, but there were still signs of resistance popping up in some places—resistance ratios went as high as 28.07. The most worrying pockets were Bara Bandai and Kuza Bandai, where pyrethroid resistance was strongest across the board.

Conclusion: pyrethroid resistance in Ae. aegypti is both widespread and uneven in Swat. Cypermethrin and alphacypermethrin are not good options anymore for dengue control. Deltamethrin and lambda-cyhalothrin still work in some places, but they are losing ground and need to be managed wisely. This situation makes it clear: regular resistance monitoring, rotating insecticides, and using integrated vector management are not just helpful—they are essential if dengue is to be controlled in the region in a sustainable manner.

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