LD50S BY TOPICAL APPLICATION AND COMPARATIVE INITIAL AND RESIDUAL TOXICITY OF PYRETHROID, ORGANOCHLORINE AND ORGANOPHOSPHORUS INSECTICIDES IN FIELD TESTS AGAINST THE BOLL WEEVIL

摘要

LD50s of methyl parathion and fenpropathrin ranged from 0.0027 to 0.0089 mu g/weevil, indicating susceptibility. The LD50 of methidathion was 0.037 mu g/weevil, indicating susceptibility. On 0 d one spray each of cyfluthrin, lambda cyhalothrin, bifenthrin and zeta cypermethrin to cotton plants showed 5% to 30% mortality of boll weevils. Seven d later the mortalities were within this same range. On 0 d one spray each of malathion, endosulfan and azinphosmethyl showed 90% to 100% mortalities. Azinphosmethyl, malathion and endosulfan caused 70%, 30% and 12% mortality after seven d, respectively. Mortalities for cyfluthrin, zeta cypermethrin and lambda cyhalothrin peaked at 95%, 70% and 72% on 3, 2 and 3 d, respectively. This suggests a repellency by pyrethroids on 0 and 1 d. Field tests with season long sprays of bifenthrin and endosulfan alone, a mixture and alternate applications of the insecticides showed variation in efficacy, determined by damaged squares, against the boll weevil in 1993 and 1994. In 1993 endosulfan, the mixture and alternate applications of bifenthrin and endosulfan were significantly more effective than the untreated. In 1994, none of the treatments were significantly more effective than the untreated. Damage levels were the greatest in 1994.