Aphicidal activities of Moroccan Bacillus thuringiensis strains against cotton aphid (Aphis gossypii)

Abstract

The objective of this study was to evaluate the insecticidal effect of toxins from Moroccan Bacillus thuringiensis strains (Berliner) (Bt) on Aphis gossypii (Homoptera: Aphididae). Aphis gossypii is one of the most pests of Moroccan crops. Their management is based traditionally on using chemical products. Some of them are well known to be potentially toxic to the environment and human health. Therefore, alternative strategies for aphid management in crops have been developed in recent years, including a biological control using toxins of bacterial strains. In this study, the artificial diet bioassay was used to screen the aphicidal effect of 82 Bt toxins against first instar nymphs and third instar nymphs of A. gossypii. Among the examined Bt strains, eleven showed a high insecticide activity against A. gossypii stages. In addition, the assessment of the lethal concentration (LC50) of selected Bt revealed that the local BtA4, BtA1 and Bt21.6 exhibited higher insecticidal activity against first instar nymphs of A. gossypii (LC50 (BtA4)=0.15, LC50 (BtA1)=0.23 and LC50 (Bt21.6)=0.25 mg/ml) and the selected strains BtB6, BtA10 and Bt21.6 exhibited the relatively best activity third instar nymphs of A. gossypii (LC50 (BtB6)= 0.48, LC50 (BtA10)= 0.79 and LC50 (Bt21.6)= 1.14 mg/ml) of A. gossypii. Therefore, the results of this study indicate that the selected B. thuringiensis strains have great potential to be used in the integrated A. gossypii management.