Monitoring of insecticide sensitivity change in different developmental stages of the cotton whitefly, Bemisia tabaci (genn.)to certain insecticides

摘要

Efficiency of six insecticides (three organophosphated, two carbamates, and one synthetic pyrethroid) to different developmental stages of susceptible (S-) and field (F-) strains of the aleyrodid cotton pest, Bemisia tabaci (Genn.), was determined in the laboratory using leafdip technique. Based on the LC_50 values, the egg stage, within the same strain, seemed to be less sensitive for the most insecticides tested, comparing with pupal and adult sages. Concerning the anticholinesterase insecticides tested, pirimiphos-methyl and profenofos were the most potent, furathiocarb and pirimicarb occupied a moderate position, while malathion was the less potent, against egg, pupal and adult stages of S- and f-strains. Cypermethrin (synthetic pyrethroid) was the less effective compound against egg stage, but ranked the second potent compound against adult stage of S- and F-strains. Slope values for all the insecticides tested against the three stages of both strains of B. tabaci were low. Generally, egg stage of F-strain was still sensitive toward all insecticide tested (RR ranging from 0.83 to 1.25), whereas, pupal and adult stages exhibited a low level of tolerance (RR ranging from 3.50 to 5.00; from 1.67 to 5.00, for pupal and adult sages, respectively). The results were discussed in relation to monitoring insecticide tolerance in the aleyrodid, and provide information about the implication of B.tabaci tolerance.