Fly Control on Farms with Several Organic Thiophosphate Insecticides1

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Abstract
Residual fly control effectiveness of the following organic thiophosphate insecticides: isochlorthion, chlorthion, diazinon, Penthion-80, and pirazinon was evaluated on farms located near Ames, Iowa. Emulsifiable concentrate and wettable powder formulations of most insecticides were used to prepare sprays which contained a 1% concentration of the active ingredient. Fly populations on farms were estimated during summer by observing a series of natural resting places on each farm. Nearly all flies observed were either house flies or stable flies, Musca domestica. and Stomoxvs calcitrans. An approximation of residual effectiveness and species specificity of insecticide formulations was obtained also by observing the dying and newly dead flies on selected horizontal surfaces at several of the farms. All insecticides killed house flies effectively. Diazinon appeared to kill stable flies most effectively. Estimates were made of the range of residual fly control after spraying these insecticides. The following figures, based upon both over-all seasonal impressions and actual fly counts after spraying, provide an estimated range of effective fly control in days for house flies and stable flies, respectively: isochlorthion, 13-28 and 9-21; chlorthion, 3-28 and 10-28; diazinon, 8-31 and 7-35; Penthion-80, 10-14 and there were too few stable flies to make an estimate; and pirazinon, 8-22 and 7-22. A series of post-application milk samples taken at 2 dairy farms sprayed with isochlorthion and chlorthion, respectively, revealed no trace of either insecticide in the milk at any time.

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