Effect of insecticides on longevity of the whitefly, bemisia tabaci [gennadius] on cotton

ABSTRACT

The study was conducted during 2001 and 2002 for evaluating the hormoligosis of sub-lethal doses of commonly used insecticides on cotton in Punjab, India. Quinalphos [250, 375 and 500 g], carbaryl [625, 938 and 1250 g], acephate [750, 1125 and 1500 g], endosulfan [438, 656 and 875 g] and fenvalerate [25, 38 and 50 g ai/ha] were repeatedly sprayed on potted plants of American cotton [var. LH 1556]. The newly emerged ten females and ten males were released in separate micro-leaf cage for each replicate, which were attached to top fully opened cotton leaves after 72 hours of I, II. Ill, IV and V spray. The mortality of adults in each cage was counted daily. The results revealed that all insecticides caused significant reduction in longevity of both sexes except low dose of fenvalerate. Maximum reduction was recorded on all doses of endosulfan, followed by higher doses of other insecticides. In general, low doses of different insecticides caused minimum reduction in longevity, compared with higher doses. The results have clearly indicated that no hormoligosis has been induced in longevity of whitefly by the tested insecticides. Therefore, the resurgence of whitefly that reported to be associated with repeated spray of fenvalerate and acephate is not due to the hormoligosis in longevity of this pest, but may be due to other reasons