Study on the collaborative ability of Pyemotes moseri and Beauveria bassiana to control the larva of Dioryctria sylvestrella

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.