Toxicity of natural insecticides on the larvae of wheat head armyworm, Dargida diffusa (Lepidoptera: Noctuidae)

Abstract

The wheat head armyworm, Dargida (previously Faronta) diffusa (Walker) (Lepidoptera: Noctuidae), is widely distributed in North American grasslands and is most common on the Great Plains, where it is often a serious pest of corn and cereal crops. Six commercially available botanical or microbial insecticides used against D. diffusa were tested in the laboratory: Entrust® WP (spinosad 80%), Mycotrol® ESO (Beauveria bassiana GHA), Aza-Direct® (azadirachtin), Met52® EC (Metarhizium brunneum F52), Xpectro® OD (Beauveria bassiana GHA + pyrethrins), and Xpulse® OD (Beauveria bassiana GHA + azadirachtin). Concentrations of 0.1, 0.5, 1.0 and 2.0 fold the lowest labelled rates of formulated products were tested for all products, while for Entrust WP additional concentrations of 0.001 and 0.01 fold the label rates were also assessed. Survival rates were determined from larval mortality at 1–9 days post treatment application. We found that among the tested chemicals, Entrust® (spinosad) was the most effective, causing 83–100% mortality (0–17% survival rate) at day 3 across all concentrations. The others, in order of efficacy from most to least, were Xpectro® (B. bassiana GHA + pyrethrins), Xpulse®OD (B. bassiana GHA + azadirachtin), Aza-Direct®(azadirachtin), Met52® EC (M. brunneum F52), and Mycotrol® ESO (B. bassiana GHA). These products and entomopathogenic fungi caused 70–100% mortality (0–30% survivability) from days 7 to 9. The tested products and entomopathogenic fungi can be used in management of D. diffusa.