The toxins produced by Bacillus thuringiensis (Bt) are well known for their insecticidal activity against Lepidoptera, Diptera and Coleoptera; however, the sap-sucking insects (Hemiptera) are not particularly susceptible to Bt toxins. We describe the aphicidal effect of Cry toxin from Bt strain GP919 against one of the most pernicious hemipterans in the agricultural environment, Myzus persicae. The mortality bioassay shows that the strain cause mortality rates above 80% at concentration of 10 ng/µl with a LC50 of 9.01 ng/µl; whereas it showed no lethal toxicity against the lepidopteran Spodoptera frugiperda. The mayor protein (∼130 kDa) expressed by this strain was subjected to purification, solubilization and trypsin digestion, the band of ∼ 65 kDa which was obtained from trypsin digestion was purified by ion-exchange chromatography and was used to feed the aphid. The bioassay shows mortality rates above 85% at concentration of 10 ng/µl and the LC50 was 6.58 ng/µl. The resulting fragment from the digestion was identified by mass spectrometry and the candidate protein showed an overall 100% amino acid sequence identity to the reported Cry1Cb2 (WP 033698561.1) protein from Bt. Koch's postulated also was carried out with the GP919 strain and also, we document the signs of infection caused by this strain. This is the first report of a Cry1Cb2 protein that is toxic to a sucking insect and this protein may become a promising environmentally friendly tool for the control of M. persicae and possible also for other sap sucking insect pests.
Keywords: Bacillus thuringiensis; Cry1Cb2; Microbial Control; Myzus persicae.
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