A positively charged carbon dot complex improves the bioactivity of Isaria fumosorosea against Plutella xylostella (Linnaeus)

Nanomaterials compounded with entomopathogenic fungi have been proven to be effective in insect pest management. This study reports the synthesis and bioactivity of Isaria fumosorosea-based nanoparticles by compounding the fungus with differentially (positively or negatively) charged carbon dots. Initially, negatively charged carbon dots (N-CDs) and carbon dots (P-CDs) were synthesized via a one-step hydrothermal method. The N-CDs and P-CDs were then individually compounded with I. fumosorosea to develop N-CD@I. fumosorosea and P-CD@I. fumosorosea nanocomposites. Characterization of the nanoparticles revealed that positively or negatively charged carbon dots were attached to I. fumosorosea by electrostatic bonding. Finally, the virulence of both types of nanoparticles was observed in Plutella xylostella. The bioassay results indicated that the highest P. xylostella mortality (92.7 ± 2.04%) was associated with the P-CD@I. fumosorosea treatment. The results of nontargeted metabolomic analysis revealed that different treatments affected the metabolism of P. xylostella by interfering with the riboflavin metabolism pathway by downregulating the expression of two main metabolites of the riboflavin metabolism pathway (2-5-diamino-6-pyrimidin-4-one and 7-hydroxy-6-methyl-8-ribiotin), although the extent of the expression downregulation varied among the different treatments. Overall, this work provides insight into the mechanism by which positively charged nanomaterials improve the virulence of entomopathogenic fungi. This work provides a new direction for the design and application of nanomaterials for insect pest management.