Enhancement of Transfer of Technical Malathion From Cotton Leaves to Boll Weevils Using Cottonseed Oil
Transfer tests of technical malathion alone and in mixtures of different ratios of cottonseed oil (CSO) were conducted in the laboratory. A Potter spray tower was used to treat cotton leaves excised from plants grown in a greenhouse. Mixtures of malathion:CSO were applied first at constant volume and then at constant rate. CSO was found to enhance transfer of malathion from cotton leaves into boll weevils. Mortality and the amount of malathion transferred to weevils were related to the rate of malathion, the amount of CSO in the mixture, and the volume applied. A three-parameter modified Weibull Function was found to best fit the data. Two types of data were fit. First, maximum cumulative mortality was found to increase with increasing volumes of malathion and a steady state of insecticide transfer to the boll weevil was reached within 5 - 15 cm of travel across a treated cotton leaf. The distance at which half of the maximum cumulative mortality occurred increased as the volume of application increased. Also the rate of cumulative mortality over distance traveled increased when malathion was mixed with CSO. All mixtures except the 1:1 ratio of malathion:CSO had greater maximum cumulative mortalities than an undiluted application of malathion. The highest ratio, 1:9, produced the greatest maximum cumulative mortality (99%) and transferred the greatest amount of malathion from cotton leaves to boll weevils. The second type of data modeled by the cumulative Weibull function was the malathion residue that was transferred to boll weevils as they traveled various distances across leaves treated with various mixtures. Cumulative malathion residue on boll weevils for each treatment followed similar trends as cumulative mortality.