Cotton Arthropod Food Chain Disruptions by Pesticides in the San Joaquin Valley, California 1

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Abstract
Populations of the western flower thrips, Frankliniella occidentalis (Pergande) and 2 important predators (Geocoris pallens Stall; Orius tristicolor White) were monitored in relationship to cotton plant growth and chemical applications for lygus bug control in the San Joaquin Valley, California. F. occidentalis abundance was closely correlated with the blooming of the cotton. Reduction of G. pallens from the multiple dimethoate and naled-toxaphene applications in 1971, and from dimethoate treatments in 1972 allowed the thrips population to increase significantly. O. tristicolor was the predator most correlated with the thrips population. Predator mortality was reflected in the number of beet armyworm, Spodoptera exigua (Hübner), larvae which arose in the late season 1971 and by cabbage looper, Trichopulsia ni (Hübner), larvae in 1972. Differential crop damage due to differences in larval numbers led to 21.5% greater cotton lint yield per ha in 1971 in plots treated with naled-toxaphene in comparison to plots treated with dimethoate. In 1972, the untreated plots netted 48 and 80 more per ha than plots treated with dimethoate or aldicarb, respectively.

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