Laboratory Screening Tests of Animal Systemic Insecticides

Abstract

Systemic, insecticidal properties of candidate insecticides received at. the Kerrville, Texas, laboratory are determined by the following short-term laboratory test. Guinea pigs, infested with nymphal lone star ticks ( Amblyomma americanum (L.)) and screw-worms ( Callitroga hominivorax (Cqrl.)) are treated orally or subcutaneously with the compounds. After treatment, stable flies ( Stomoxys calcitrans (L.)) are fed on the guinea pigs. From many compounds which have been screened, results of tests with nine are presented to illustrate variations in toxicity to the arthropods and lethality to the guinea pigs. Am. Cyanamid 12,880 ( O, O -dimethyl S -(N-methylcarbamoylmethyl) phosphorodithioate), ( S -2-(ethylsulfinyl)ethyl O, O - dimethyl ester phosphorodithioic acid), and Bayer 23,453 ( S -2-(ethylsulfiuyl) ethyl O, O -dimethyl ester phosphorodithioic acid) were toxic to all three species. Bayer 21/199 and Dow ET-57 were toxic to screw-worms and stable flies but not lone star ticks. Hercules AC-528, Tedion, Thiodan, and Trithion were ineffective. Compounds which showed promise in tests with guinea pigs were tested further in sheep and goats, being administered as drenches to sheep infested with screw-worms and to goats infested with screw-worms and lone star ticks. After treatment, stable flies were fed on the goats. In addition to entomological data, this test is used by cooperating veterinarians to obtain toxicological data. Am. Cyanamid 12,880, Bayer 23,129, and Dow ET-57, used in tests with sheep and goats, were all effective against screwworms, and 12,880 was also effective against the other arthropods.