Screening of Fungal Strains and Formulations of Metarhizium anisopliae to Control Phyllotreta striolata in Chinese Flowering Cabbage

Abstract

(1) Background: The cabbage flea beetle (CFB; Phyllotreta striolata) seriously damages the production of Chinese flowering cabbage (CFC; Brassica campestris L. ssp. chinensis var. utilis), which is a key leafy vegetable in South China. A large number of chemical insecticides have been sprayed to control this pest; as a result, residues and resistances are becoming an issue. It is necessary to develop biocontrol technologies to address this issue. (2) Methods: Fungal strains were selected based on bioactivity against CFB, and CFC seed pelletization with fungal conidia was subject to evaluation of control efficacy against CFB. The effective mixture of fungus and chemical insecticide was determined based on safety and joint toxicology tests. (3) Results: The screening of 103 strains from 14 genera identified the Metarhizium anisopliae strain MaGX19S02 (Ma) as the one with the highest virulence. The LC50s of Ma to CFB adult and second instar larvae on day 9 post-treatment were 3.04 × 106 and 27.2 × 106 spores/mL, respectively. In the pot test, the pelletization of CFC seeds with Ma conidia (50/25/12.5 mg in 1 g seed with 4 g fillers) demonstrated significant CFB mortalities (45–82%) 20 days after the larvae were introduced. In the field test, the seed pelletization achieved 57–81% control efficacy 14 days after sowing. Furthermore, the combination of Ma with chlorfenapyr (Chl) demonstrated a synergistic effect against CFB; based on this result, we prepared the mixture formulation of 20% Ma-Chl wettable powder (WP). The assessment of the effects of 20% Ma-Chl WP (500× diluent) against CFB revealed 93.33% mortality in the pot test and 61.3% control efficacy in the field test on day 7 post-treatment. (4) Conclusions: The findings demonstrate the potential of Ma to control CFB in the field. Seed pelletization with Ma conidia effectively controlled CFB larvae and protected CFC seedlings, wherein a mixture formulation of 20% Ma-Chl WP had substantial efficacy in controlling CFB adults. Our research provides new methods for CFB biocontrol.

In vitro Screening of Natural Metarhizium spp. Isolates for Bioinsecticidal and Biofungicidal Activity

“…10). Many researchers reported that Metarhizium species had a high virulence against such plant pathogens as B. cinerea, Fusarium spp., Phytophthora megasperma, Podosphaera fuliginea, Pythium spp., Rhizoctonia solani, Sphaerotheca fuliginea and Verticillium dahliae [59,61,62,63,64].…”

The Striped Flea Beetle <i>Phyllotreta striolata</i> (Illiger) (Coleoptera: Chrysomelidae) Invades South India

“…Tengfei et al (2022) suggested the use of a seed-pelletized coating of spinetoram for its control in cabbage. Chen et al (2023) has shown that seed pelletization with conidia of Metarhizium anisopliae effectively controlled the larvae and protected Chinese flowering cabbage seedlings, wherein a mixture formulation of M. anisopliae and chlorfenapyr demonstrated a synergistic effect against the adults. Maulik (1926), who published the first comprehensive study of the flea beetles of the Indian subcontinent under the Fauna of British India series, did not record P. striolata in India or adjoining areas.…”