Diel susceptibility of the boll weevil, Anthonomus grandis boheman to certain organophosphorous insecticides

Abstract

Studies were conducted to determine the effect of the thermoperiod and photoperiod on the diel sensitivity of the boll weevil, Anthonomus grandis Bohemn, to organophosphorus insecticides. Other studies related to insecticide sensitivity, respiration and locomotion were also investigated. Experiments to develop a satisfactory technique for applying insecticide to boll weevils were conducted. The topical method of treating weevils with insecticide produced less variability than tests using a drench or a filter paper surface technique. The latter 2 methods were not different from each other. Boll weevils entrained in various thermoperiods at LD9:15 were treated topically with malathion at dawn and dusk. Weevils treated at dawn were more tolerant to the insecticide than those treated at dusk. In a similar experiment when weevils were caged on malathion treated cotton plants, moralities were 56 percent at dawn and 86 percent at dusk. Greater mortality was produced with equivalent dosages of insecticides in warm temperature than in cooler temperature regimens. Other experiments 4 techniques for treating boll weevils with malathion. In all treatments insects were treated hourly for 24 consecutive hours in photoperiods of LD10:14, 12:12 and 14:10. In each regimen weevils were more resistant to malathion at dawn than at dusk. In the majority of tests, the percentages of weevils killed were greater for those insects treated during the photofraction that the scotofraction. Mortalities from weevils entrained in LD10:14 were greater than for weevils in LD14: 10..