Specificity of Bacillus thuringiensis Delta-Endotoxin.

Area of Science:

• * Entomology
• * Microbiology
• * Biochemistry

Background:

• * Bacillus thuringiensis (Bt) produces delta-endotoxins, a key component in biological pest control.
• * Understanding the factors influencing Bt toxin efficacy is crucial for optimizing pest management strategies.

Purpose of the Study:

• * To evaluate the insecticidal activity of delta-endotoxins from 14 Bacillus thuringiensis strains against three key insect pests.
• * To investigate the role of crystal solubility and insect susceptibility in Bt toxin potency.

Main Methods:

• * Assessed insecticidal activity of purified delta-endotoxin crystals against Pieris brassicae, Heliothis virescens, and Spodoptera littoralis larvae.
• * Examined the effect of crystal predissolution on insecticidal activity.
• * Compared the efficacy of in vitro-activated toxins across different insect species.

Main Results:

• * Significant variations in susceptibility were observed among insect species and Bt strains.
• * B. thuringiensis subsp. thuringiensis and B. thuringiensis subsp. morrisoni were most effective against P. brassicae.
• * B. thuringiensis subsp. kenyae and B. thuringiensis subsp. kurstaki showed highest efficacy against H. virescens.
• * B. thuringiensis subsp. entomocidus crystals were most potent against S. littoralis.
• * Crystal solubility in insect gut juice was identified as a critical factor for toxin activation and efficacy.
• * Predissolution of crystals enhanced insecticidal activity, particularly against H. virescens.

Conclusions:

• * The insecticidal potency of Bacillus thuringiensis delta-endotoxins is influenced by a combination of factors.
• * These factors include the specific Bt strain origin of the toxin, the solubility of the toxin crystals within the insect's gut, and the intrinsic susceptibility of the target insect species.