Effect of bioinsecticides on the grey maize weevil Tanymecus dilaticollis

Abstract

Tanymecus dilaticollis is an important pest of maize and sunflowers in eastern Europe. In the present study, we examined the effectiveness of two commercially available bioinsecticides against T. dilaticollis adults under laboratory conditions: Naturalis^® based on the Beauveria bassiana fungus and an azadirachtin-based botanical product NeemAzal T/S^®. Our results suggested that adults of the pests are more susceptible to B. bassiana than to azadirachtin. Naturalis^®, tested at six concentrations (2.3 × 10²– 2.3 × 10⁷ conidia/mL), showed a high lethal effect to T. dilaticollis adults, and 100% corrected mortality was observed in the treatments over 2.3 × 10⁵ conidia/mL and 2.3 × 10⁶ conidia/mL for females and males, respectively. NeemAzal T/S^®, tested at four concentrations (0.5, 1, 2 and 4%) with two treatments, caused generally low to moderate mortality – 6–44% within 16 days. A field experiment consisted of two sprayings of maize experimental plots with Naturalis^® at a rate of 200 mL/0.1 ha and then the recording the number of dead adults of T. dilaticollis in the treated and control plots was conducted in north-western Bulgaria. Twenty days after treatment, a significantly higher mean mortality of the pest caused by the mycoinsecticide than in the control variants was registered.