LABORATORY STUDIES OF SUSCEPTIBILITY AND RESISTANCE TO INSECTICIDES IN PEDICULUS-CAPITIS (ANOPLURA, PEDICULIDAE)

The susceptibility of local head lice to permethrin, sumithrin, deltam ethrin, and carbaryl was determined by laboratory bioassays in field-c ollected colonies. Head lice collected from the infested heads of chil dren 6-12 yr old were tested within 3 h of collection. The longest sur vival of control insects in the laboratory was obtained by keeping the m in the dark at 18 degrees C and 70-80% RH. The base line susceptibil ity data obtained for insects collected from children not treated for lice, the reference colony, showed that deltamethrin caused the highes t mortality of the insecticides tested (LC50, 0.06%). Permethrin, sumi thrin, and carbaryl showed no significant difference in mortality (sup erposition of confidence intervals), being 10 times lower than that ca used by deltamethrin All field-collected lice required a higher LC50 o f permethrin than the reference colony. Resistance levels varied from 3 to >100 for colonies that were taken from children treated with anti -lice products. Lice colonies with permethrin resistance showed resist ance to sumithrin and deltamethrin, but resistance was not observed to the carbamate carbaryl.