Toxicological Studies on the Egyptian Cotton Leafworm, Prodenia litura. IV. The Toxicity of Pyrethrins, Allethrin, and Cyclethrin to Prodenia Larvae and the Effect of Synergists1

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Abstract
By topical application pyrethrins are very toxic to the larvae of the Egyptian cotton leafworm, Prodenia litura (F.). However, topically applied pyrethrins are twice as toxic as allethrin and cyclethrin. The toxicity of 9 pyrethrin-synergist combinations is determined. The pyrethrin synergist S-421 (bis-(2,3,3,3 tetrachloropropyl) ether) is found to be a very effective contact insecticide to Prodenia larvae. Pyrethrins and cyclethrin are synergized to a higher degree than allethrin by the synergists used. MGK 264 (N-(2-ethylhexyl)-5-norbornene-2,3-dicarboximide) and AR-10 (N,N-dibutyl-p-chlorobenzenesulfonamide) (WARF anti-resistant) are poor synergists for the 3 insecticides to Prodenia larvae. Sulfoxide, Safroxan (4-(3,4-methylenedioxyphenyl)- 5- methyl-m-dioxane), sesamex, and Bucarpolate (2-(2-butoxyethoxy)ethyl piperonylate) are the most effective synergists on the 3 insecticides to Prodenia larvae. Piperonyl butoxide and piperonyl cyclonene are intermediate in their synergistic effect on pyrethrins and cyclethrin, but are poor with allethrin. Generalized equations are formulated to determine the degree of synergism of a synergist and to compare it to others. When the dosage of the pyrethroid insecticides used is below LD20, maximum efficiency for the pyrethroid-synergist combinations is obtained.