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Entomopathogenic fungi, when used as a microbial control agent against cotton pests, such as Helicoverpa spp., may have the potential to establish and spread in the environment and to have an impact on both pests and beneficial insects. Information on the effect of entomopathogenic fungi on pests and beneficial insects is crucial for a product to be registered as a biopesticide. The effect of the entomopathogenic fungus BC 639 (Aspergillus sp.) against Helicoverpa spp. and beneficial insects (mostly predatory insects) was studied in the laboratory and in cotton field trials. The results show that when Helicoverpa spp. second instar larvae were exposed to increasing concentrations (from 10² to 109) of the entomopathogenic fungus BC 639, the optimum dose required to kill over 50% of the insects was 1.0 × 107 spores/mL. In the field trials, the number of Helicoverpa spp. per metre on plots treated with 1.0 or 0.50 L/ha of BC 639 was the same as on plots treated with the recommended rate of the commercial insecticide, Indoxacarb. However, when plots were treated with 0.25 L/ha of BC 639, this was not as effective at controlling Helicoverpa spp. as 1.0 or 0.5 L/ha BC 639 or Indoxacarb. BC 639 had less effect on predatory insects when applied at lower rates (0.50 and 0.25 L/ha) than at higher rates (1.0 L/ha). Thus, BC 639 was more selective against predators when applied at lower rates than at the higher rate, but was also more selective than Indoxacarb. Thus, the ability of BC 639 to control Helicoverpa spp. effectively with a minimal effect on predatory insects indicates its potential for enhancing integrated pest management programs and to sustain cotton production. [ABSTRACT FROM AUTHOR]