Toxicity and persistence of three pyrethroids for the control of cereal bugs on common wheat

Sunn pests are responsible for serious kernel damage on wheat (Triticum aestivum L., Poaceae), affecting bread-making quality from their feeding at the late milk-ripe stage. In this study the toxicity of three pyrethroids usually applied to this crop (lambda-cyhalothrin, alpha-cypermethrin, tau-fluvalinate) was evaluated on two bug species, the wheat bug Eurygaster maura (L.) and the green stink bug Nezara viridula (L.) in both laboratory and semi-field conditions, to implement an effective and sustainable control strategy. Laboratory trials showed small differences between the insecticides, whereas field cage trials gave more information on toxicity and persistence of the three pyrethroids. The most toxic and with good persistence on plants was alpha-cypermethrin, followed by lambda-cyhalothrin, which had an intermediate persistence. By contrast, tau-fluvalinate showed a high persistence on plants, but seemed unsuited for wheat bug control because of its low toxicity, as clearly demonstrated in both laboratory and semi-field trials. The results provide clear information on the application strategy of the tested pyrethroids. In this context, alpha-cypermethrin proved to be the most promising active ingredient for wheat bug control, particularly for early application of the insecticide in a mixture with a fungicide at the wheat heading stage, eliminating the need for a separate additional treatment by the farmer.