Alterations in microbial community structures and metabolic function in soil treated with biological and chemical insecticides.

Entomopathogenic fungi show significant promise as effective and ecological friendly alternatives to chemical insecticides for insect pest control. However, little is known concerning their effects on soil ecosystems, especially in comparison to application of chemical insecticides. Here, we examined the effects of one biological and two chemical insecticides, Metarhizium anisopliae, imidacloprid (IMI) and emamectin benzoate (EMB) on microbial community structure, metabolic functioning, and soil biochemistry. Treatment with EMB and IMI, reduced Actinobacteriota populations, while increasing that of Acidobacteriota. However, these populations were not significantly altered under M. anisopliae treatment. Chemical pesticides also altered fungal communities including potential pathogens. Activities of soil beneficial nitrogen-cycling-related enzymes were reduced after application of IMI and EMB, but were increased after treatment with M. anisopliae. Metagenomics analysis showed that IMI treatment reduced levels of carbon and nitrogen-related metabolic pathways. However, M. anisopliae treatment increased representation of key enzymes involved in the carbon, nitrogen, and sulfur cycling important for maintenance of soil fertility. Insecticides treatments altered the abundance of a number antibiotic resistance genes (ARGs) but not virulence factors (VFs), whereas application of M. anisopliae resulted had only minimal effects. These findings highlight the consequences of use of biological vs. chemical pesticides on soil microbiology can affect plant and ecosystem health indicating that the fungal biological control agent, M. anisopliae likely has far less detrimental and potentially beneficial effects on soil ecology as compared to chemical pesticides.