Pyrethroid Susceptibility in Stomoxys calcitrans and Stomoxys indicus (Diptera: Muscidae) Collected from Cattle Farms in Southern Thailand

Abstract

The susceptibility to six pyrethroid insecticides (permethrin, deltamethrin, alpha-cypermethrin, cypermethrin, lambda-cyhalothrin, and bifenthrin), each at the recommended concentration, was evaluated for two stable fly species-<i>Stomoxys calcitrans</i> (Linnaeus, 1758) and <i>Stomoxys indicus</i> Picard, 1908 (Diptera: Muscidae)-through tarsal contact using a World Health Organization (WHO) cone bioassay procedure. The field populations of <i>S. calcitrans</i> were collected from the Songkhla and Phattalung provinces, while <i>S. indicus</i> were collected from the Phattalung and Satun provinces in Thailand. The stable flies were exposed to insecticide-treated filter paper for 30 min, and their knockdown counts at 30 min and 60 min and mortality counts at 12 h and 24 h were recorded. The <i>S. calcitrans</i> and <i>S. indicus</i> Songkhla and Phattalung populations were moderately susceptible to pyrethroids, as indicated by the 24 h mortality. Nonetheless, the Satun population of <i>S. indicus</i> was completely susceptible to permethrin, with 100% mortality, and showed the lowest susceptibility to deltamethrin and bifenthrin. The results indicate the generally low susceptibility of stable flies to pyrethroids in the southern provinces of Thailand.