After the tender shoots, branches and other parts of pine species such as Pinus koraiensis are damaged by the larvae of Dioryctria sylvestrella, there often appear cohesive resinous masses at the damaged parts. As a result, a variety of control measures cannot directly reach the larvae beneath the resinous masses, thus reducing the control efficiency. Therefore, it is necessary to provide an efficient and green prevention and control method to control the population density of this pest and improve the control effect.

Based on the determination that Pyemotes moseri is not infected by Beauveria bassiana, this study screened the adjuvants including 0.1% starch (SS), glucose (Glu), Tween-80, and potato dextrose (PDS) according to the time and quantity of B. bassiana CFCC81428 spores passively carried by P. moseri, as well as the activity of the carried spores. Then, a simulation test was carried out under semi-natural conditions to determine the lethal effects on the larvae of D. sylvestrella inside the branches of Pinus koraiensis on the 3rd, 5th, and 7th days when only P. moseri was released and when P. moseri carrying B. bassiana with adjuvants was released.

P. moserii carried the largest number of B. bassiana spores under the treatment of 0.1% glucose-dispersed spore suspension. After being treated for 2 and 4 h, the mite could carry 6.50×10⁴ spores and 3.72×10⁴ spores of B. bassiana, respectively, and form 15.67 and 15.33 colonies with a diameter of 3mm on the medium. On the third day after releasing P. moserii into the branches of P. koraiensis, the control effect of the larvae was (65.00%±3.54%). On the third day after releasing P. moserii, the control effect reached (71.31%±7.14%), the larvae had Beauveria colonies.

0.1% glucose (Glu) solution could be used as a highly adsorptive adjuvant to prolong the time and number of spores carried by P. moserii, and improve the activity of B. bassiana spores B. bassiana could enter the tunnel from the coagulating mass of the damaged parts of the branches of P. koraiensis to control the larvae of D. sylvestrella, and there were swelling bodies and B. Bassiana colonies on the surface of the larvae, it improved the possibility of breeding and survival of P. moseri and biocontrol strains in the release area, and laid a foundation for the follow-up P. moseri and biocontrol strains to control the larvae of T. mellonella.

Beauveria bassiana was screened and its pathogenicity on larvae and adults of Hylurgus ligniperda was investigated, the infection process of B. bassiana on larvae and adults of H. ligniperda was verified.

1) Morphological identification and molecular biology identification were used to determine the strain of the selected strains; 2) The cumulative corrected mortality rate was calculated using Excel 2016 and the SPSS 26.0 was used for ANOVA and the virulence regression equation and LC50 were calculated; 3) Electron microscopy scanning was used to observe the infection of larvae and adults of H. ligniperda.

1) Through bioassay, it was found that 4 strains of B. bassiana were not the same virulence to the larvae and adults of H. ligniperda, named Bbz1, Bbz2, Bbz3 and Bbz4; 2) Among them, the strain Bbz4 had the best poisoning effect on larvae, after inoculation for 5 days, the killing effect of 1×10⁸ spores/mL concentration of spore suspension on the larvae of H. ligniperda reached 100%, LC₅₀ was 3.68×10⁵ spores/mL. The best poisoning effect on the adult of H. ligniperda was the strain Bbz1. After inoculation for 5 days, the killing effect of 1×10⁸ spores/mL concentration of spore suspension on the alduts of H. ligniperda reached 100%, and the LC₅₀ was 3.27×10⁶ spores/mL; 3) Scanning electron microscopy was performed on the infection of larvae and adults of H. ligniperda used strain Bbz4 and strain Bbz1, and it was found that the conidia of these strains touched and attached to the body surface of H. ligniperda during 0-12 h after inoculation. When inoculated for 18 h, spore germination was found and bud tubes were produced; At 36 h, there was mycelium penetrating the body wall; When inoculated for 72 h, hyphae appeared on the surface of the worm; At 96-120 h of inoculation, the entire body was covered with hyphae.

It was determined that four different strains of B. bassiana were isolated from the body of H. ligniperda, among which strains Bbz4 and Bbz1 were the most pathogenic to the larvae and adults of H. ligniperda, and determined their infection process on H. ligniperda at different time points after inoculation.