Effect of imidacloprid stress on growth of resistant and susceptible strain of yeast-like symbiote, Candida lipolytica, isolated from rice brown planthopper, Nilaparvata lugens Stål

In order to understand the effect of imidacloprid stress on the growth of resistant and susceptible strain of yeast-like symbiote, Candida lipolytica, the number of colonies cultured on solid medium and the growth amount of different strains of C.lipolytica cultured in liquid medium contained different concentrations of imidacloprid were compared by methods of strain culturing, colony observation and microscope examination of mycelium. The results showed that different concentrations of imidacloprid had inhibitory effects on the growth of resistant and susceptible strains of C.lipolytica; and the higher concentration of imidacloprid, the stronger the inhibitory effect. The number of colonies of susceptible strain treated with 500, 1 000 and 2 000 mg/L imidacloprid for four days were only 46.61%, 27.58% and 6.25% of the control, respectively, which were all significantly different with that of the control. The number of colonies of resistant strain treated with 2 000 mg/L imidacloprid were also significantly different with that of the control, however, that of 500 and 1 000 mg/L treatment were not. After being treated with imidacloprid, the morphology of susceptible strains of C.lipolytica became abnormal, for example, some mycelia were not stretched, became atrophy or bending, the top of mycelia appeared swollen, and yeast vacuoles generated; and the higher concentration of imidacloprid treated, the higher degree of abnormal was observed; the abnormal morphology of resistant strain was similar with that of susceptible strain, but the proportion of abnormal mycelia declined significantly. At treatment of 500 mg/L imidacloprid, the growth and dry weight of mycelia of resistant and susceptible strains were not affected significantly; while at treatment of 1 000 and 2 000 mg/L imidacloprid, the growth of different strains was inhibited significantly in the early stage, but was not affected obviously in the later stage. In conclusion, the effect of imidacloprid on the growth of resistant strain of C.lipolytica was significantly less than that of susceptible strain.