Abstract: 【Aim】To identify the species of culturable symbiotic bacteria in the brown planthopper, Nilaparvata lugens, explore the effects of the symbiotic Bacillus spp. on the microbiota and growth and development of N. lugens. 【Methods】 The culturable symbiotic bacteria were isolated from two different virulent populations of N. lugens (the susceptible population TN1 and the virulent population IR56) by in vitro culture. The obtained cuttural symbiotic bacteria were identified by 16S rDNA sequencing technology. On this basis, the distribution of symbiotic bacteria in N. lugens was studied by in situ hybridization. The effects of reducing symbionts and supplementation of Bacillus spp. on the growth and development of N. lugens, as well as the abundance of symbionts, were studied using artificial diet added with antibiotics or symbiotic Bacillus spp. The effects of introducing symbiotic Bacillus spp. through feeding and microinjection methods were compared, and the correlation between Bacillus spp. colonization and the virulence of TN1 population was investigated. 【Results】 In total 15 strains of different symbiotic bacteria were obtained from N. lugens by in vitro culture, including 2 strains of the symbiotic Bacillus spp. (BPH-S36 and BPH-S33) from the highly virulent population IR56. The result of in situ hybridization showed that symbiotic bacteria were distributed in the salivary glands, gut, fat body and female internal genitalia of N. lugens, but rarely in the male internal genitalia. Symbionts are crucial for the growth and development of N. lugens. The reduction of symbiotic bacteria led to a significant decrease in the survival rate of N. lugens on the 3rd and 6th day, while supplementing the symbiotic Bacillus BPH-S33 or BPH-S36 resulted in a significant increase in the survival rate of N. lugens on the 6th day. The relative abundance of Bacillus spp.in N. lugens increased by 23.2-24.5-fold by feeding on the artificial diet supplemented with the symbiotic Bacillus spp., but not increased through microinjection into nymphs. With the increase of the symbiotic Bacillus spp., the relative abundance of yeast-like symbiont (YLS) also significantly increased by 5-12-fold. Introduction of Bacillus strain BPH-S36 significantly increased the survival rate of N. lugens TN1 population on the resistant rice IR56 from 52.1%±1.5% to 64.2%±3.0%. 【Conclusion】Symbiotic bacteria are widely distributed in the salivary glands, gut and ovaries of N. lugens. Antibiotic treatment can significantly reduce the abundance of symbiotic bacteria in their bodies and result in a decline in survival rate. The exogenous symbiotic bacteria colonize successfully in N. lugens through artificial feeding. Bacillus strain BPH-S36 derived from the IR56 population can improve the population virulence to the resistant rice variety IR56.
Key words: Nilaparvata lugens; symbiotic bacteria; yeast-like symbiont; virulence; Bacillus spp.; adundance