Comparative efficacies of two fungal insecticides in field control of cereal aphids heavily infesting winter wheat

Sustainable control of cereal aphids during late spring and early summer requires alternatives to mitigate increasing resistance to chemical insecticides. Emulsifiable oil-formulated Beauveria bassiana ZJU435 (Bb) and Metarhizium anisopliae CQ421 (Ma) commercially registered in China were tested as alternatives against the aphids Rhopalosiphum padi and Sitobion avenae, which infested 29% of winter wheat tillers with ~11 aphids per tiller at elongating stage, followed by rapid population growth. Bb and Ma were sprayed biweekly at the low and high rates of 1.0 × 10¹³ and 1.5 × 10¹³ conidia ha⁻¹ over five weeks of three independent field trials from elongating to milk ripening stages. In four fungal treatments (three randomized plots of 100 m² per treatment), percent tiller infestation and aphid density were reduced respectively to 19–23% and 9.5–15.8 aphids per tiller, contrasting with 53% and 63 (~110 at peak) aphids per tiller in unsprayed control throughout the field trials. Overall mean (±SE) control efficacies of Bb and Ma assessed with weekly sampled aphid densities were 85% (±0.3) and 80% (±0.6) at the high rate and 79% (±0.6) and 75% (±0.8) at the low rate, and differed significantly with each other at either spray rate (P < 0.01). Conclusively, both Bb and Ma were highly efficacious against cereal aphids, and Bb was superior to Ma perhaps due to a lower rate of larger Ma conidia deposited on wheat plants at either spray rate. Their high efficacies were attributed to the qualified formulation and the season warming up with frequent drizzles to favor fungal aphidicidal activity.