The response of Beauveria bassiana to zinc exposure in controlling Hyphantria cunea: Short-term efficiency improvement and long-term efficiency reduction.

Essential metal elements are common environmental pollutants in insect habitats. In this study, a Zinc (Zn)-contaminated food chain composed of soil, Fraxinus mandshurica, and Hyphantria cunea larvae was established to assess the response of Beauveria bassiana (Bb) to zinc exposure in controlling H. cunea larvae. Zn exposure significantly increased the sensitivity of H. cunea larvae to Bb. The cellular immune response of H. cunea larvae in the Zn-treated group was markedly suppressed both before and after Bb infection. Additionally, the expression of genes involved in humoral immune pathogen recognition and key regulatory genes in the Toll/IMD signaling pathway was significantly reduced in Zn-treated larvae, both pre- and post-infection. Zn exposure alone could up-regulate the expressions of the antimicrobial peptide genes Attacin, Lebocin, Lysozym, Cecropin and Gloverin by 3.84, 1.42, 2.06, 2.68 and 1.86 times, respectively. The combined treatment of Zn and Bb can down-regulate the expressions of Lebocin, Cecropin and Gloverin by 48.67%, 23.16% and 40.85%, respectively. Zn exposure also impaired the nutritional content and energy metabolism of H. cunea larvae. The performance of Bb spores on the body surface of Zn-treated larvae was notably reduced, leading to a decreased mortality rate in subsequent larvae. In conclusion, under Zn exposure, the short-term pest control performance of Bb against the H. cunea is enhanced, but Bb long-term persistence in pest control is weakened.