Effect of Chemical and Microbial Insecticides on Several Insect Pests of Lettuce in Southern California1

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Abstract
Six experiments were conducted during 1959 and 1960 to evaluate and compare the toxicities of a variety of chemical and microbial insecticides to western flower thrips, Frankliniella occidentalis (Pergande), green peach aphids, Myzus persicae (Sulzer), and larvae of the cabbage looper, Trichoplusia ni (Hubner), on lettuce, Most of the microbial dust preparations containing Bacillus thuringiensis Berliner var. thuringiensis provided effective control of the cabbage looper, including the large larvae which are very difficult to control with most chemicals, at application rates between 20 and 35 pounds of formulated material per acre. Sprays of B. thuringiensis were notably inferior to dusts. Of the chemical insecticides, Zectran® (4-dimethylamino-3,5-xylyl methylcarbamate) at 0.5 pound, Dibrom® (1,2-dibromo-2,2-dichloroethyl dimethyl phosphate), Guthion® (O,O-dimethyl S-( 4-oxo-1,2,3-benzotriazin-3-(4H)-ylmethyl) phosphorodithioate), and American Cyanamid 24055 (1,1-dimethyl-3-(p-acetamidophenyl)triazene) at approximately 1 pound, and DDT+toxaphene at 1.9+5.6 pounds per acre gave fair to good control of cabbage looper larvae. Repeated applications of parathion at 1 pound and DDT+toxaphene at 1.5+3 pounds per acre provided excellent control of green peach aphids and western flower thrips. In addition, single applications of Zectran at 0.5 pound and Dibrom, Dylox® (O,O-dimethyl 2,2,2-trichloro-1-hydroxyethyl phosphonate), Guthion, malathion, and ronnel at approximately 1 pound per acre suppressed populations of the western flower thrips.