关键词: 灰飞虱, 异常毕赤酵母, 离体培养, 杀菌剂, 生物防治, 变性梯度凝胶电泳

Abstract: 【Aim】 With the extensive application of chemical pesticides, the small brown planthopper,  Laodelphax striatellus has increased its resistance to pesticides so that the control effect of pesticides on L. striatellus is weakened. Therefore it is crucial to explore a new method for controlling this pest. In this study, we attempt to inhibit the abundance of symbiotes inside L. striatellus by fungicides to weaken the vitality of this pest, so as to provide a theoretical foundation for controlling L. striatellus through inhibiting yeast-like symbiont (YLS). 【Methods】 The yeast-like symbiont was isolated from L. striatellus via in vitro culture and the susceptibility of the isolated YLS to different concentrations of fungicides was examined. The fungicides with apparently higher ability to inhibit the growth of YLS were applied on wheat seedlings used for feeding L. striatellus. The mortality and body weight of L. striatellus adults were measured and the variation of the amount of YLS inside L. striatellus was examined through real-time florescent quantitative PCR. 【Results】 A strain of YLS was successfully isolated and identified as  Pichia anomala based on the corresponding carbon assimilation experiment and 18S rDNA phylogenic analysis. Denaturing gradient gel electrophoresis (DGGE) result further confirmed the existence of this strain in L. striatellus. The test results of sensitivity to fungicides indicated that 70% propineb and 50% tebuconazole+25% trifloxystrobin had obvious inhibitory effects on the growth of P. anomala while fluopicolide+ propamocarb hydrochloride（687.5 g a.i./L） and 40% pyrimethanil had relatively less inhibitory effects on the growth of P. anomala.When two fungicides (70% propineb and 50% tebuconazole +25% trifloxystrobin with obvious inhibitory effect were applied on wheat seedlings at the concentration of 800 mg/L, the mortality of L. striatellus adults feeding the treated wheat seedlings reached 46.7% and 63.3%, respectively, which was apparently higher than that of the control group, and the body weight of L. striatellus adults in the treatment group was also less than that of the control group. Real-time florescent quantitative-PCR results indicated that the amount of YLS of three strains (Hypomyces chrysospermus, Pichia guilliermondii, and P. anomala) inside L. striatellus dropped sharply after different fungicides were applied. 【Conclusion】 The results suggest that the fungicides applied in vitro on  L. striatellus  have inhibitory effects on their YLS, thus impacting the survival of L. striatellus, and this validates the feasibility of “reduction in use of pesticides through use of fungicides” strategy in controlling L. striatellus.

Key words:  Laodelphax striatellus, Pichia anomala, in vitro culture, fungicide, biological control, denatured gradient gel electrophoresis (DGGE)