Specificity of Bacillus thuringiensis Delta-Endotoxin

Abstract

The insecticidal activity of the delta-endotoxins of 14 Bacillus thuringiensis strains belonging to 12 subspecies was determined against Pieris brassicae, Heliothis virescens, and Spodoptera littoralis. Larvae of P. brassicae were highly susceptible to purified crystals of strains of B. thuringiensis subsp. thuringiensis and B. thuringiensis subsp. morrisoni, whereas H. virescens responded best to B. thuringiensis subsp. kenyae and B. thuringiensis subsp. kurstaki. The crystals of the B. thuringiensis subsp. entomocidus strain were the most potent against S. littoralis. It was shown that the solubility of the crystals within the gut of the three insect species is a first important step in the mode of action. Predissolution of the crystals especially enhanced the insecticidal activity against H. virescens. When in vitro-activated toxins were applied, the relative potency range varied greatly from one insect species to another. It can be concluded that at least three factors influence the potency of B. thuringiensis delta-endotoxins: the strain-related origin of the toxin, the degree of solubility of the crystals in the gut juice, and the intrinsic susceptibility of the insect to the toxin.

Susceptibility of Cydia pomonella to Bacillus thuringiensis under laboratory and field conditions

“…delta-endotoxin. The LC50 for C. pomonella was 1.0 #g/ml of purified kurstaki HD-73 crystals whereas 1.2/~g/ml of the most active strain (kenyae, 4430) was required for Heliothis virescens, using the same bioassay system (Jaquet et al, 1987). However due to the feeding behaviour of the neonate larvae, B.t.…”

BACILLUS THURINGIENSIS USE IN AGRICULTURE: A MOLECULAR PERSPECTIVE

“…There are two functionally distinct regions in the N-terminal domain of the lepidopteran-active (Cry I) toxins : a common region (between amino acid residues 29-300), and a hypervariable region ranging approximately between amino acids 300 and 650 (Brousseau & Masson, 1988;Jacquet et al, 1987). Comparisons of the aligned sequences of different Cry proteins have revealed the existence of five highly conserved sequence blocks within the whole of this N-terminal portion (Hofte & Whiteley, 1989).…”

Neither barium nor calcium prevents the inhibition by Bacillus thuringiensis δ‐endotoxin of sodium‐ or potassium gradient‐dependent amino acid accumulation by tobacco hornworm midgut brush border membrane vesicles

“…Parasporal crystals were separated from the other components of sporulated cultures using a two-phase extraction system with dextran sulfate and polyethylene glycol [20]. This procedure has been shown routinely to yield crystals contaminated by less than 1% spores [21]. The purified crystals were suspended at approximately 10 mg/ml in 1 mM EDTA.…”