Acaricide Screening for Control of Psoroptic Mites, 1979

Normally, common scabies mites, Psoroptes ovis (Hering), were obtained from Government-owned cattle for acaricide tests. During the summer months when these mites were not available, we used Psoroptes cuniculi (Delafond) taken from the ears of rabbits for these tests. Approximately 20 to 25 mites (adults or nymphs) were put In "tea bags" (2.5 cm^) made from heat-sealable rice paper (Wright and Riner, 1979. Southwest. Entomol. 4:40-45). The 64 acaricides were tested as technical materials formulated as emulsifiable concentrates (EC) containing 25% active ingredient, 65% xylene, and 10% Triton X-100 or as company supplied emulsifiable concentrates or wettable powders. Because of solubility problems, some were formulated as 10 or 20% EC’s in xylene: Triton X-100 or in mixtures of N-methyl-2-pyrrolidone, xylene, and Triton X-100. Three bags containing mites were dipped in each concentration of the acaricides for 30 sec and then were allowed to dry at room temperature and ambient humidity. Mites that served as controls were dipped in dilute solvent and emulsifier at concentrations equivalent to those used in the acaricide emulsions. The bags were opened 24 hours post treatment, and the mites were observed with the aid of a dissecting microscope and scored as dead or alive. Mites scored as dead were immobile or had only feeble leg movement. Mites scored as alive were able to travel normally. The highest concentration of acaricide tested was 0.1%. If 100% kill was obtained at 0.1%, more dilute concentrations (0.01%, 0.001%, 0.0001% …) were tested until mortality was less than 100%. Compounds were rated on the basis of the scoring as: