Detection of insecticide resistance and knockdown resistance (kdr) mutations in Aedes albopictus across different regions.

OBJECTIVE: This study aimed to monitor the resistance status of adult Aedes albopictus (Ae. albopictus) to commonly used insecticides in Jining (Shandong Province), Guangzhou (Guangdong Province), and Haikou (Hainan Province), and to provide evidence for improving vector control strategies. METHODS: Between May and July 2024-2025, field-collected Ae. albopictus larvae from the three regions were reared under laboratory conditions. Adult insecticide susceptibility was assessed using the WHO tube test. Species identity was confirmed morphologically under a dissecting microscope. Genomic DNA was extracted from individual female mosquitoes, and fragments of the voltage-gated sodium channel (VGSC) gene were amplified by PCR and sequenced. kdr mutations were analyzed using BioEdit software. RESULTS: Across the three regions, 24-hour mortality rates of Ae. albopictus exposed to 0.03% deltamethrin, 0.4% permethrin, and 0.08% lambda-cyhalothrin were all below 80%, indicating resistance. For 0.05% propoxur, mortality rates were 100%, 79.21%, and 98.17% in Jining, Guangzhou, and Haikou, respectively. For 0.5% malathion, mortality rates were 88.12%, 98.06%, and 88.12%, respectively. In Guangzhou, mortality rates for 0.08% beta-cyfluthrin and cis-cypermethrin were both below 80%, while in Jining and Haikou, they ranged from 86.17% to 93.88%. Mutations were detected at VGSC codons 1016, 1532, and 1534 in all three populations. The GGA/G allele at codon 1016 was found only in Guangzhou (4.17%). At codon 1532, a single mutant allele (ACC/T) was detected (2.43%), with three genotypes observed: I/I (96.12%), I/T (2.91%), and T/T (0.97%). At codon 1534, five alleles were identified: TTC (F) (35.44%), TCC (S) (24.27%), TGC (C) (38.35%), TTG (L) (1.46%), and CTC (L) (0.49%), forming seven genotypes, including F/F (18.44%), F/C (6.80%), F/S (23.30%), F/L (3.88%), S/S (7.77%), C/C (30.10%), and S/C (9.71%). CONCLUSION: The studied Ae. albopictus populations showed high resistance to three commonly used pyrethroid insecticides, while relatively lower resistance was observed for propoxur and malathion. kdr mutation frequencies varied across regions, with generally low mutation rates at codon 1016. The mutation frequency at codon 1534 was lower in Jining than in Guangzhou and Haikou, whereas codon 1532 showed a relatively higher mutation frequency in Jining. These findings highlight the importance of rational insecticide use, continuous resistance monitoring, and rotation of insecticides to delay resistance development and spread.