AUTHOR=Zhao Jie , Chen Yuxi , Keyhani Nemat O. , Wang Cong , Li Yichen , Pu Huili , Li Jincheng , Liu Sen , Lai Pengyu , Zhu Mengjia , He Xueyou , Cai Shouping , Guan Xiayu , Qiu Junzhi 

TITLE=Isolation of a highly virulent Metarhizium strain targeting the tea pest, Ectropis obliqua

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1164511

DOI=10.3389/fmicb.2023.1164511

ISSN=1664-302X

ABSTRACT=<sec><title>Introduction</title><p>Tea is one of the most widely consumed beverages around the world. Larvae of the moth, <italic>Ectropis obliqua Prout</italic> (Geometridae, Lepidoptera), are one of the most destructive insect pests of tea in China. <italic>E. obliqua</italic> is a polyphagus insect that is of increasing concern due to the development of populations resistant to certain chemical insecticides. Microbial biological control agents offer an environmentally friendly and effective means for insect control that can be compatible with “green” and organic farming practices.</p></sec><sec><title>Methods</title><p>To identify novel <italic>E. obliqua</italic> biological control agents, soil and inset cadaver samples were collected from tea growing regions in the Fujian province, China. Isolates were analyzed morphologically and via molecular characterization to identity them at the species level. Laboratory and greenhouse insect bioassays were used to determine the effectiveness of the isolates for <italic>E. obliqua</italic> control.</p></sec><sec><title>Results</title><p>Eleven isolates corresponding to ten different species of <italic>Metarhizium</italic> were identified according to morphological and molecular analyses from soil and/or insect cadavers found on tea plants and/or in the surrounding soil sampled from eight different regions within the Fujian province, China. Four species of <italic>Metarhizium</italic> including <italic>M. clavatum, M. indigoticum, M. pemphigi</italic>, and <italic>M. phasmatodeae</italic> were documented for the first time in China, and the other species were identified as <italic>M. anisopliae, M. brunneum, M. lepidiotae, M. majus, M. pinghaense</italic>, and <italic>M. robertsii</italic>. Insect bioassays of the eleven isolates of <italic>Metarhizium</italic> revealed significant variation in the efficacy of each isolate to infect and kill <italic>E. obliqua</italic>. <italic>Metarhizium pingshaense</italic> (MaFZ-13) showed the highest virulence reaching a host target mortality rate of 93% in laboratory bioassays. The median lethal concentration (LC<sub>50</sub>) and median lethal time (LT<sub>50</sub>) values of <italic>M. pingshaense</italic> MaFZ-13 were 9.6 × 10<sup>4</sup> conidia/mL and 4.8 days, respectively. Greenhouse experiments and a time-dose-mortality (TDM) models were used to further evaluate and confirm the fungal pathogenic potential of <italic>M. pingshaense</italic> MaFZ-13 against <italic>E. obliqua</italic> larvae.</p></sec><sec><title>Discussion</title><p>Isolation of indigenous microbial biological control agents targeting specific pests is an effective approach for collecting resources that can be exploited for pest control with lowered obstacles to approval and commercialization. Our data show the presence of four different previously unreported <italic>Metarhizium</italic> species in China. Bioassays of the eleven different <italic>Metarhizium</italic> strains isolated revealed that each could infect and kill <italic>E. obliqua</italic> to different degrees with the newly isolated <italic>M. pingshaense</italic> MaFZ-13 strain representing a particularly highly virulent isolate potentially applicable for the control of <italic>E. obliqua</italic> larvae.</p></sec>