Laboratory Studies to Determine the Effectiveness of DDVP Sprays for Control of Locusts2

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Abstract
The requirements of insecticide formulations for use against. the desert locust, Schistoeerea gregaria (Forskål), are described. DDVP is shown to be more toxic and quick acting than other insecticides in common use (LD50's: DDVP 1.8-4.3, diazinon 4.7, and BHC (gamma isomer) 9.0 μg./g . of body weight). The toxicity of DDVP in oil solution by contact action decreased when it was applied in concentrated form (LD50's: 1.8 in 3.5- ,5.0% wt./vol. solution and 3.3 μg/g . of body weight in 35% wt./vol. solution in the distillates KEB or LPD), and was found to be very dependent on the exact nature or the solvent used. The rate or evaporation of the insecticide was determined at 30° C.; free-falling lOO-micron droplets of pure DDVP were estimated to lose nearly 1% of their active ingredient per metre of fall. Droplets of DDVP in dioetylphthalate and dutrex 3 lost the active ingredient at a faster rate. The vapour toxicity also was determined (CT50=1.0 g. sec./m.3) and shown to be of little importance compared with the toxicity of sprays (CT50= 1.6 × 10-3 g.sec./m.3). DDVP was found to be partially cumulative (LD50increased by one third when dose was applied in two halves separated by a 72-hour interval) and 1.8 times more toxie when applied to the wings than to the abdomen of the desert locust. Used in dilute solution,DDVP would have to compete in price with the cheaper BHC and aldrin. The properties of the concentrates do not suggest that DDVP would find general use in locust control until means can be found to reduce its rate of evaporation.