Pyrethroid insecticides susceptibility of Stomoxys calcitrans (Linnaeus) and Stomoxys indicus Picard (Diptera: Muscidae) 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 the two stable fly species Stomoxys calcitrans (Linnaeus) and Stomoxys indicus Picard, through tarsal contact using a World Health Organization (WHO) cone bioassay procedure. The field populations of stable flies were collected from three study sites (Songkhla, 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 hr and 24 hr were recorded. The S. calcitrans and S. indicus in Songkhla and Phattalung populations were moderately susceptible to pyrethroids for 24-hr mortality. Nonetheless, the Satun population of S. indicus was completely susceptible to permethrin with 100% mortality and the lowest susceptible to deltamethrin and bifenthrin. The results indicate a generally low susceptibility of stable flies to pyrethroids in the southern provinces of Thailand.