Aphicidal activity of Bacillus thuringiensis strain AH‐2 against cotton aphid (Aphis gossypii)

Abstract

AbstractBacillus thuringiensis (Bt) is the most commercialized entomopathogenic species. However, the low efficacy against notorious sap‐sucking Hemipteran pests and the high costs of production, reduce the applicability of Bt biopesticides. In this context, B. thuringiensis AH‐2 (Bt‐2) isolated from soil was found to release parasporal inclusions and aphicidal activity. Bt‐2 showed optimal growth at pH 8 and 30°C in tryptic soy broth (TSB) and maintained normal growth when cultured in cost‐effective test media, pink brown (PB), supplemented with either glucose (PBG) or sucrose (PBS). To study aphicidal activity against cotton aphid (Aphis gossypii), Bt‐2 and a commercial B. thuringiensis subspecies kurstaki (Btk) were used. Using third nymph (3 N) instars, treatment with Bt‐2 caused 70.2, 78.1 and 88.4% mortality at 10, 25 and 50% culture concentrations, respectively. Similarly, Btk resulted in 79.9, 80.4 and 92.9% mortality at 10, 25 and 50%, respectively. When cultured in TSB, PBG and PBS media, Bt‐2 culture (50%) resulted in 85.9, 82.9 and 82.2% 3 N mortality, respectively. Equally, Btk caused a mortality of 79.9, 78.9 and 78.9% in TSB, PBG and PBS, respectively. Bt‐2 exerted a notably higher aphicidal efficacy at 24 h after treatment compared to Btk, especially at low concentration. Moreover, both Bt strains significantly suppressed adult fecundity compared to control. At 50% culture concentration, Bt‐2 and Btk suppressed adult fecundity by 98.3 and 91.1%, respectively. Our result demonstrates a strong aphicidal efficacy of Bt‐2, and its potential production using cost‐effective PB medium.