Compatibility of Zineb, dimethoate and Beauveria bassiana (Balsamo) Vuillemin against tarnished plant bug (Hemiptera: Miridae)

Abstract

Experiments were conducted under laboratory and field conditions to assess the effect of the fungicide Zineb (zinc dimethyl-dithiocarbamate) and the insecticide Cygon (dimethoate) on the pathogenicity of the isolate MK 2001 of Beauveria bassiana (Balsamo) Vuillemin, a potential microbial agent for biological control of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois). The isolate was highly pathogenic to adults yielding an LC50 of 7.2 × 103 conidia/mL at 6 d post treatment and an LT50 of 3.07 d at a concentration of 1 × 108 conidia/mL. Zineb inhibited the in vitro growth of the fungus in Sabouraud's dextrose broth and on Sabouraud's dextrose agar. It had no insecticidal activity against adult L. lineolaris in laboratory bioassays. A field test with caged L. lineolaris adults on lettuce Lactuca sativa L. var. longifolia, at a phenological stage of 50 leaves further demonstrated that Zineb and Dimethoate had no effect on B. bassiana against L. lineolaris. Adult mortality 10 d after application did not differ significantly in treatments with B. bassiana alone from treatments with B. bassiana + Zineb, dimethoate alone, B. bassiana + dimethoate, B. bassiana + Zineb, and B. bassiana + Zineb + dimethoate. No larva was observed in cages treated with B. bassiana alone or in combination with Zineb or dimethoate. On the contrary, 11 larvae/plant were recorded in the untreated cages and 5 larvae/plant in the dimethoate-treated cages.