Engineering Beauveria bassiana with Spider-Derived Hv1a Neurotoxin Enhances Biocontrol Efficacy Against Piercing–Sucking Insect Pests

Entomopathogenic fungi such as Beauveria bassiana are important biological control agents that provide alternatives to chemical insecticides; however, their application is often limited by relatively slow killing rates. In this study, we engineered the B. bassiana Bb2860 strain to express the spider-derived neurotoxin gene Hv1a and evaluated the biological characteristics and insecticidal activity of the recombinant strain. Bb2860-Hv1a was constructed using a blastospore-mediated LiAc/PEG transformation system and confirmed by PCR and Western blot analyses. Re-isolated recombinant fungi retained detectable Hv1a expression following host infection. Hv1a expression did not affect colony growth or conidial production under laboratory conditions. Bioassays using different infection approaches showed that the effects of Hv1a expression varied among insect species and experimental conditions. Bb2860-Hv1a did not significantly enhance insecticidal activity against G. mellonella, Spodoptera litura, or Ostrinia furnacalis larvae in immersion assays, but shortened the LT50 of O. furnacalis larvae from 5.20 to 4.15 days in hemocoel injection assays. Foliar spray assays showed enhanced mortality of Bb2860-Hv1a compared with the wild type against Aphis gossypii, Myzus persicae, Frankliniella occidentalis, and Bemisia tabaci, with final mortality rates of 62.22%, 68.89%, 60.00%, and 95.56%, respectively, and LT50 values of 4.86, 5.61, 5.92, and 4.87 days. Collectively, these results indicate that Hv1a expression can enhance the insecticidal activity of B. bassiana under specific bioassay conditions, particularly against several piercing–sucking pests evaluated by spray application. This study provides a basis for further evaluation and optimization of Hv1a-expressing B. bassiana as a potential fungal biocontrol candidate.