This invention discloses a strain of *Backusella circina* and its application. The strain number of *Backusella circina* is JSAFC 2057, which was deposited at the China General
Microbiological Culture Collection Center (CGMCC) on September 23, 2024, with accession number CGMCC No. 41522. This
fungal agent can significantly inhibit the survival activity of the
fall webworm (*Triplophysa fulvidraco*), reducing the survival activity of
fall webworm larvae to zero after 7 days of treatment and culture. The
fungus provided by this invention is a biocontrol
fungus for the control of the major pest, the
fall webworm. It is characterized by strong
pathogenicity against fall webworm larvae,
environmental safety, and low likelihood of inducing
pesticide resistance in pests, and can be applied to the biological control of the fall webworm.