Comparative laboratory evaluation of insecticide susceptibility in two striped flea beetle (Phyllotreta striolata) populations from Chinese cabbage fields

Abstract

Despite extensive insecticide use in crucifer production systems, information on local susceptibility of Phyllotreta striolata in northern Thailand remains limited. This study evaluated the susceptibility of adult P. striolata collected from Mae Na Chon, Chiang Mai Province, and Ban Huai Pong, Chiang Rai Province, Thailand, to eight insecticides using a laboratory leaf-dip bioassay. A total of 3,280 adults were tested in 41 treatments per population, with four replicates of 10 insects per treatment. Mortality was recorded at 24, 48, and 72 h after exposure and analyzed using dose-response models, Fisher's exact tests, and binomial generalized linear models. Susceptibility differed among active ingredients, exposure times, and populations. Chlorantraniliprole showed contrasting LC₅₀ values between populations, with 24-h LC₅₀ values of 2757.29 ppm in Mae Na Chon and 1.73 ppm in Ban Huai Pong. Fipronil showed low LC₅₀ values in both populations (2.27 and 3.35 ppm at 24 h), whereas cartap hydrochloride showed similar LC₅₀ values between populations at 72 h (96.59 and 97.88 ppm). Several compounds, including chlorantraniliprole, lambda-cyhalothrin, carbaryl, and acetamiprid, showed population-dependent responses. These results provide baseline data for resistance monitoring and support insecticide selection based on local susceptibility rather than assuming uniform efficacy across production areas.