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

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- Stomoxys calcitrans (Linnaeus, 1758) and Stomoxys indicus Picard, 1908 (Diptera: Muscidae)-through tarsal contact using a World Health Organization (WHO) cone bioassay procedure. The field populations of S. calcitrans were collected from the Songkhla and Phattalung provinces, while S. indicus 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 S. calcitrans and S. indicus Songkhla and Phattalung populations were moderately susceptible to pyrethroids, as indicated by the 24 h mortality. Nonetheless, the Satun population of S. indicus 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.