Efficacy of Biorational Insecticides and Entomopathogenic Fungi for Controlling Cassida vittata Vill. (Coleoptera: Chrysomelidae) in Sugar Beet Crops

The sugar beet flea beetle, Cassida vittata Vill. (Coleoptera: Chrysomelidae), is a major pest in Morocco’s sugar beet crops and is primarily controlled with chemical insecticides despite environmental concerns. Our aim was to assess the impact of three biorational insecticides (spinosad at 30–7.5 cc/hL, mineral oil at 2000–250 cc/hL, and potassium salts of fatty acids at 1500–375 cc/hL) and two entomopathogenic fungi (Alternaria murispora and Alternaria destruens applied at 1.0 × 10⁸, 5.0 × 10⁷, and 2.5 × 10⁷ conidia mL⁻¹) both individually and in combination on C. vittata adults. All treatments were conducted at 25 ± 1 °C, with mortality recorded over 10 days. Conidial germination was highest for A. murispora with mineral oil (98.4%). Alternaria destruens showed consistently high germination across treatments. At 100% concentration, A. murispora + mineral oil and A. destruens + mineral oil treatments achieved 96.67 and 92.00% mortality, respectively. Median survival times (MST) for A. murispora were 6.0 days at 100% concentration, increasing to 10.0 days at lower concentrations, while A. destruens had a consistent 10.0 days MST. LC₅₀ for A. murispora was 1.3 × 10⁷ conidia mL⁻¹ alone, increasing to 2.2 × 10⁷ with spinosad, but remained 1.7 × 10⁷ with potassium salts of fatty acids. For A. destruens, LC₅₀ was 4.2 × 10⁷ conidia mL⁻¹ alone, decreasing to 1.5 × 10⁷ with mineral oil, and 3.1 × 10⁷ with potassium salts of fatty acids. Combining A. murispora with mineral oil and potassium salts of fatty acids enhanced efficacy against C. vittata.