Objective  To lay the foundation of the development of new insect-resistant biological pesticides in trees, the insect-resistant function of the serine protease inhibitor PtrSPI of Populus tomentosa was studied.

  Method  To analyze the function of serine protease inhibitor gene PtrSPI, the promoter and the expression pattern under feeding stress of Lymantria dispar larvaes of the gene PtrSPI in P. tomentosa were studied. To discuss the anti-insect ability of PtrSPI, the food intake, the body mass, the mortality and the serine protease enzyme activities of L. dispar larvae were studied after using the eukaryotic recombinant protein PtrSPI feeding L. dispar larvaes.

  Result  The results showed that 5 elements related to plant resistance to disease and insects were in the promoter region of the serine protease inhibitor gene PtrSPI of P. tomentosa; the expression pattern of the gene PtrSPI in P. tomentosa leaves was firstly decreased and then increased after being fed by L. dispar larvae, and the peak was 2.03 times of the control at 30 h; under the high concentration of recombinant protein (300 and 500 mg/mL), the food intake and the body mass of L. dispar larvaes were significantly inhibited, the mortality of L. dispar larvaes was up to more than 60% after 4 and 6 days, respectively, and the activities of the serine protease in L. dispar larvaes were significantly increased at the beginning of feeding.

  Conclusion  This study verifies the insect resistance of the serine protease inhibitor PtrSPI of P. tomentosa, and it provides theoretical basis and research materials for further research and development of new non-pollution and insect-resistance biological pesticides.