Suppression of Rice Planthopper Populations by the Entomopathogenic Fungus Metarhiziumanisopliaewithout Affecting the Rice Microbiota

Abstract

Entomopathogenic fungi can regulate insect populations and function as crucial biological control agents against insect pests, but their impacts on nontarget microorganisms are poorly understood. In this study, we investigated the potential of the fungal strain Metarhizium anisopliae CQMa421 to control rice planthoppers under field conditions and its effects on rice microbiota. This fungus suppressed rice planthoppers during this period, and its control efficiency was more than 60% 7 days post application and did not significantly differ from that of the chemical treatment except in 2019. Both treatments showed a lower population of rice planthoppers than the controls. After application, M. anisopliae was maintained on rice plants for approximately 14 days, showing a decreasing trend over time. Furthermore, the results showed that the bacterial and fungal richness (operational taxonomic units) and diversity (Shannon index) did not significantly differ between the fungal treatment and the controls after application. The major bacterial taxa of Proteobacteria (including Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Deltaproteobacteria), Actinobacteria, Bacteroidetes and Cyanobacteria accounted for more than 80% of the bacterial community after fungal application, and the major fungal taxa of Ascomycota (including Eurotiomycetes, Dothideomycetes and Sordariomycetes), and Basidiomycota (including Ustilaginomycetes) represented more than 90% of fungal community. However, the microbial communities of the rice phyllosphere did not significantly change after entomopathogenic agent application, indicating that the indigenous microbial communities may adapt to fungal insecticide application. Taken together, the results suggest that this fungal agent has good potential for rice planthopper control with no substantial effects on rice microbial communities. IMPORTANCE Entomopathogenic fungi may be used as crucial biocontrol agents for the control of insect pests, but few effective fungal strains have been reported for the control of the rice planthopper, a major pest of rice. More importantly, the impacts of fungal insecticide application on nontarget microorganisms have not been well evaluated, especially under field conditions. Therefore, in this study, we investigated the effects of the fungal strain M. anisopliae CQMa421 on rice planthopper populations from 2017 to 2019 and evaluated its potential impacts on the microbiota of rice plants after application. The results suggested that this fungal agent has good potential for use in the control of rice planthoppers with no significant effects on rice microbial communities, representing an alternative strategy for the control of rice pests.

Timing of Fungal Insecticide Application to Avoid Solar Ultraviolet Irradiation Enhances Field Control of Rice Planthoppers

“…The overall mean efficacy of RPH control by either fungal insecticide in three field trials was significantly higher in the treatment of UVavo (~77%) than of UVexp (~65%) on day 14 after the first spray. These observations were in agreement with the RPH control efficacy of 50-70% observed in the previous field trials of M. anisopliae CQ421 under undisclosed weather conditions [32,33]. The repeated spray of each fungal insecticide provided a consistent RPH control for two more weeks.…”

“…Application of B. bassiana granules to the water surface in contact with rice plants led to as effective an RPH control as a spray of conidia under controlled conditions [31]. Field trials with a formulation of M. anisopliae CQ421 showed a RPH control efficacy of 50-70% on day 7 after spraying and little impact on native microbiota [32,33]. The same formulation has also proved effective for the sustainable control of major rice insect pests, including leaf folders and stem borers as well as RPH, with minimal effects on natural enemies of those pests, in multiple provinces of China during 2011-2018 [34].…”

Genome-Wide Identification and Analysis of Nilaparvata lugens microRNAs during Challenge with the Entomopathogenic Fungus Metarhizium anisopliae

“…In our previous study, we isolated the fungal M. anisopliae strain CQMa421 to challenge N. lugens nymphs and adults, which resulted in high mortality. Additionally, this fungus has been suggested for use in long-term control under field conditions and has relatively limited effects on nontargets species (i.e., microbial diversity and structure) [ 22 ]. Although a few studies focused on the transcriptomic level of N. lugens under stressful conditions, less attention has been paid to the analysis of this fungus at the posttranscriptional level, especially under entomopathogenic fungal challenge.…”

“…In our previous study, we found that the fungus M. anisopliae CQMa421 exhibited great potential for the control of major rice pests, including the rice planthopper N. lugens [ 21 ]. This fungal agent can also suppress the population of rice planthoppers to a low level under field conditions [ 22 , 23 ]. However, the underlying molecular interactions between the rice planthopper and the fungus are poorly understood, although this knowledge may enhance potential fungal agents for other pest control.…”