Evaluation of Insecticides for Control of Stored-Product Insects

Effectiveness of 48 insecticides was compared against adults of the Angoumois grain moth, Sitotraga cerealella (Olivier); confused flour beetle, Tribolium confusum Jacquelin duVal; granary weevil, Sitophilus granaries (L.); saw-toothed grain beetle, Oryzaephilus surinamensis (L.); and larvae of Trogoderma parabile Beal. Insects were sprayed with 0.001, 0.01, 0.1, and 1.0% w/v concentrations of insecticide dissolved in 19:1 acetone-olive oil solvent mixture. Mortalities were recorded after post-treatment exposure of 24 hr for adult insects and 48 hr for larvae. Available data on mammalian toxicity limited the number of effective compounds selected for more detailed toxicological investigations and provided the basis for tentatively grouping insecticides for practical tests according to their potential in sanitation programs. Organophosphorus compounds approximately equal to or safer than malathion were grouped for potential use as commodity protectants, direct spray applications, and residual surface treatments. Bay 77488 ( O,O -diethyl phosphorothioate O -ester with phenylglyoxylonitrile oxime), Bay 78182 ( O,O -diethyl phosphorothioate O -ester with ( O -chlorophenyl) glyoxylonitrile oxime), Bay 78755 ( O,O -diethyl phosphorothioate O -ester with (2, 6-dichlorophenyl) glyoxylonitrile, beta-isomer) , and Gardona® (2-chloro-1-(2, 4, 5-trichlorophenyl) vinyl dimethyl phosphate) killed 100% of the 5 species of test insects at I or more of the concentrations used. Malathion, Abate® ( O,O -dimethyl phosphorothioate O,O -diester with 4, 4' thiodiphenol), and C 9491 (0-2, 5-dichloro-4-iodophenyl O,O -dimethyl phos-phorothioate) were ineffective against larvae of T. parabile , but they were effective against the other 4 species. Insecticides grouped for potential use as direct sprays and residual surface treatments in sanitation programs were less safe than malathion but equal to or safer than diazinon. Of the compounds included in this group, Bay 37341 ( O,O -diethyl o -[4-(methylthio)-3, 5-xylyIJphosphorothioate), Bay 41831 ( O, O -dimethyl 0-4-nitro-mtolyl phosphorothioate), Bay 79330 ( O,O -diethyl phosphorothioate O -ester with (2,6-dichlorophenyl) glyoxylonitrile oxime, alpha isomer), C 8874 (0-(2,5-dichloro-4-iodophenyl) O, O -diethyl phosphorothioate), CP 53926 ( O,O -dimethyl S-(N-formyl- N -methylcarbamoylmethyl) phosphorodithio. ate), diazinon, dicapthon, Dursban® ( O,O -diethyl O -3, 5, 6-trichloro-2-pyridyl phosphorothioate), and fenthion killed 100% of all species of test insects at I or more concentrations of spray. CP 47114 ( O,O -dimethyl O -4-nitromtolyl phosphorothioate) was relatively ineffective against T. parabile larvae, but was effective against the other species. Dichlorvos was the only compound tested with known value for its vapor activity and usefulness in direct spray applications. It was effective against all species, and killed 100% of the Angoumois grain moths at the lowest concentration. Carbamate insecticides were grouped for comparison with Baygon® ( O -isopropoxyphenyl methylcarbamate). Mobam® (benzo[b]thien-4-yl methylcarbamate) was the only compound in this group to give complete control of all species at 1 or more of the concentrations used. Bay 62863 (2, 3-dihydro-2-methyl-7-benzofuranyl methylcarbamate) was effective against 4 species, but it failed to kill all T. para bile larvae at the highest concentration. Eight compounds were equal to or more effective than Baygon, but each showed tolerance to 2 or 3 species of test insects. Differences observed among species in susceptibility to carbamate insecticides indicated a need for further work in this area with a wide range of stored-product insects.