Selection and characterization of Bacillus thuringiensis strains toxic against pyralid stored‐product pests

Abstract

In this study, we present the selection and the characterization of Bacillus thuringiensis strains toxic against pyralid pests of stored products. Among 201 new B. thuringiensis strains isolated from different countries, two strains (BLB249 and BLB384) showed greater toxicity than the commercialized strain B. thuringiensis kurstaki HD1 against Ephestia kuehniella larvae. Morphological, molecular and biochemical investigations revealed that these strains were similar to HD1 but presented different cry gene content. Additional bioassays revealed that only strain BLB249 displayed higher toxicity than HD1 against Plodia interpunctella larvae. The study of Cry protoxin activation by midgut proteases of E. kuehniella and P. interpunctella larvae supported that higher toxicity of BLB249 and BLB384 strains compared to HD1 was not due to differential protoxin activation. Moreover, the toxic strains produced δ‐endotoxins and spores in similar amounts to HD1. Interestingly, the δ‐endotoxin production and the yield of BUPM26 strain were 32.87% and 35.12% greater than that of HD1. The potent insecticidal activities of BLB249 and BLB384 strains and the high level of δ‐endotoxin production by BUPM26 strain make them excellent candidates for use against E. kuehniella and P. interpunctella larvae.

Identification of Bacillus thuringiensis Strains for the Management of Lepidopteran Pests

“…In addition, among the selected strains, 1641, 1636, and 1658 displayed the highest toxicity against H. armigera as they had the lowest LC 50 values. Some studies have shown that the proportion of strains toxic to different lepidopterans is usually low as reported in our study (Valicente and Barreto 2003;Apaydin et al 2008;Santos et al 2009;Silva et al 2012;Azzouz et al 2015;Lone et al 2017). cry1Ac, cry2Aa1, cry2Ab2, cry2Ac, vip1, vip3 426 cry1Ac, cry1B, cry1C, cry1D, cry1EA/1Eb, cry1Fa/1Fb, cry2Aa1, vip1 520B cry1B, cry1C, cry1D, cry1Ea/1Eb, cry2Aa1, cry2Ab2, vip1, vip2, vip3 1636cry1Ac, cry1B, cry1G, cry2Aa1, cry2Ab2, vip2, vip3 1641cry1Ac, cry1B, cry1D, cry1Ea/1Eb, cry1G, cry2Aa1, cry2Ab2, vip1, vip3 1644cry1B, cry1C, cry1D, cry2Ab2, cry2Ac, vip1, vip3 1648cry1B, cry1C, cry1D, cry2Aa1, cry2Ab2, vip3 1657cry1B, cry1D, cry1Ea/1Eb, cry1Fa/1Fb, cry1G, cry2Ab2, cry2Ac, vip1, vip2, vip3 1658 We found that the strains with toxicity H. armigera their biological activity against A. gemmatalis, D. saccharalis, S. cosmioides, and C. includens.…”

An entomopathogenic bacterium strain,Bacillus thuringiensis, as a biological control agent against the red palm weevil,Rhynchophorus ferrugineus(Coleoptera: Curculionidae)

“…Much recent Bt researches have involved bioassays, mechanism of action, host physiological effects and host immunity. Azzouz et al demonstrated that the potent insecticidal activities of Bt strains BLB249 and BLB384 and the high level of δ‐endotoxin production by the BUPM26 strain made these strains excellent candidates for use against Ephestia kuehniella and Plodia interpunctella larvae . Some Bt strains showed novel toxicity and could be used to control melon fruit fly .…”

Toxin stability improvement and toxicity increase against dipteran and lepidopteran larvae ofBacillus thuringiensiscrystal protein Cry2Aa

“…E. kuehniella larvae (second instar) and A. aegypti larvae (third instar) were chilled on ice for 30 min. Larvae were dissected, and their guts were collected in a phosphate saline buffer (137 mM NaCl, 2.7 mM KCl, 10 mM Na 2 HPO 4 , 2 mM KH 2 PO 4 ) . Then, the mixture was mechanically disrupted into a blender, until homogenised, and centrifuged for 10 min at 13 000 rpm at 4 °C .…”