Preliminary Selection and Analysis of Deltamethrin-Resistant Strains ofAedes albopictusin the Laboratory

Background:Aedes albopictus is a major vector for transmission of many viral pathogens. Deltamethrin resistance was analyzed by catching A. albopictus in the field; the analysis effect is affected by many insecticides that often interact with A. albopictus in the field environment. Materials and Methods: This study examined the development of deltamethrin resistance in A. albopictus mosquitoes under controlled laboratory conditions, focusing on morphological changes, reproductive fitness, and mutation of the knockdown resistance (kdr) gene. Deltamethrin-resistant strains were selected up to the 20th generation. To determine the level of resistance, the lethal concentration 50 (LC50) of deltamethrin in the larvae was obtained, followed by the resistance ratio (RR), and in adult mosquitoes, mortality rates were calculated using the contact tube method. Results: An increase in the LC50 from 0.0070 to 0.0563 mg/L was observed in resistant versus sensitive strains, with an increase of 11.26 in the RR. Overall, the results of the larval resistance bioassay showed that resistant larvae had medium resistance; however, by the 20th generation, adult mosquitoes showed strong resistance. PCR amplification, cloning, and sequencing of sodium channel domain III gene fragments were subsequently carried out using selected resistant and sensitive female mosquitoes. As a result, a number of base mutations were observed in the kdr gene in the resistant strain; however, no amino acid sequence mutations were observed, suggesting that base sequence changes did not affect protein expression. Results of morphological changes between resistant and sensitive strains showed that significant differences in the body, foreleg, mid leg, and hind leg length, as well as wing length and width, antenna length, and proboscis length were observed between 18th-generation resistant and sensitive strains of A. albopictus. On analysis of reproductive fitness associated with deltamethrin resistance in selection of mosquitoes, observation results showed differences between resistant and sensitive strains; the female/male ratio of mosquitoes decreased after pupa hatching, with more females and fewer males. Conclusions: The model of deltamethrin-resistant selection of A. albopictus was successfully established in the laboratory. The morphological phenotypes of the deltamethrin-resistant population of A. albopictus mosquitoes had changed. The kdr gene of the 19th and 20th generations of deltamethrin-resistant A. albopictus mosquitoes had silent mutations at several sites. After deltamethrin resistance selection, the female/male ratio of mosquitoes increased after pupa hatching, with more females and fewer males, hinting at increased chances of more female mosquitoes transmitting diseases.