Analysis of the virulence, infection process, and extracellular enzyme activities of Aspergillus nomius against the Asian corn borer, Ostrinia furnacalis guenée (Lepidoptera: Crambidae)

ABSTRACT

The control of Ostrinia furnacalis, a major pest of maize in Xinjiang, is challenging owing to the occurrence of resistant individuals. Entomopathogenic fungi (EPF) are natural insect regulators used as substitutes for synthetic chemical insecticides. The fungus Aspergillus nomius is highly pathogenic to O. furnacalis; however, its virulence characteristics have not been identified. This study aimed to analyse the lethal efficacy, mode of infection on the cuticle, and extracellular enzyme activity of A. nomius against O. furnacalis. We found that the mortality and mycosis of O. furnacalis were dose-dependent when exposed to A. nomius and varied at different life stages. The egg-hatching and adult emergence rates decreased with an increase in conidial suspension. The highest mortality (83.33%, 7 d post-infection [DPI]) and mycosis (74.33%, 7 DPI) and the lowest mortality response (8.52 × 10³ conidia mL⁻¹) and median lethal time (4.91 d) occurred in the 3^rd instar larvae of O. furnacalis. Scanning electron microscopy indicated that numerous conidia germination and infection structure formation may have contributed to the high pathogenicity of A. nomius against O. furnacalis. There were significant correlations between O. furnacalis mortality and the activities of extracellular protease, lipase, and chitinase of A. nomius. This study revealed the infection process of the highly pathogenic A. nomius against O. furnacalis, providing a theoretical basis and reference for strain improvement and field application of EPF.

Graphical abstract

KEYWORDS:

• Aspergillus nomius
• ostrinia furnacalis
• lethal efficacy
• infection processes
• cuticle
• extracellular enzymes activity

Acknowledgements

This work was supported by the Natural Science Foundation of Xinjiang Uygur Autonomous Region under Grant 2022D01B35 and the Open Fund of the Key Laboratory of Integrated Pest Management of Crops in the Northwest Desert Oasis of the Ministry of Agriculture under Grant KFJJ202205.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data Availability statement

The data used to support the findings of this study are available from the corresponding author upon request.

Additional information

Funding

The work was supported by the the Open Fund of the Key Laboratory of Integrated Pest Management of Crops in the Northwest Desert Oasis of the Ministry of Agriculture [KFJJ202205]; Natural Science Foundation of Xinjiang Uygur Autonomous Region [2022D01B35].