Effects Of Endosymbionts Wolbachia On The Reproduction And Fitness Of Brown Planthopper (Nilaparvata Lugens) And Infection Density Dynamics Of Wolbachia In The Hosts

Wolbachia are maternally inherited intracellular bacteria that infect a wide range of arthropods and are associated with various reproductive abnormalities in their hosts, by which, this endosymbiont add their infection frequency in nature. The brown planthopper, Nilaparavata lugens (Stal) is a major pest of rice in China and various other countries and regions in Asia. Its seasonal northward and southward migrations, landing and endangering abruptly result in serious damage to rice production. Preliminary studies by our laboratory showed that Wolbachia was widely distributed in the Chinese populations of N. lugens. In this paper, three different populations of N. lugens were used as materials and the effects of Wolbachia on the reproduction and fitness of hosts were investigated. The infection dynamics of Wolbachia in different developmental stages of N. lugens and the infection density of Wolbachia in different tissues were also investigated using quantitative PCR. The results will explain the maintenance and spread of Wolbachia in N. lugens. Besides, we attempted to determine how the infection density of Wolbachia affects the reproduction and fitness of hosts. These results of this paper will enrich the study of relationship between endosymbiont and its host and thus provide theoretic basis for pest control.Three Chinese populations (HN, YN and GX) of N. lugens were used to investigate the effects of Wolbachia on the reproduction. We measured the strength of CI induced by Wolbachia and the sex ratio of offspring in three Chinese populations of the brown planthopper Nilaparvata lugens from Hainan, Yunnan and Guangxi provinces, respectively. No evidence for CI was found in any of the populations. Wolbachia did not cause CI in the three populations. In each population, the hatching rate of eggs for each type of cross was not significantly different. And no significant difference of sex ratio was found. Wolbachia strains infected in the HN, YN and GX populations of Nilaparvata lugens had an identical wsp gene sequence.The fitness of Nilaparvata lugens was measured by fecundity of females, longevity of adults and the vertical transmission efficiency. In the HN population, a significant effect of female infection status was found, with infected females produced more eggs in average than uninfected ones regardless of the infection status of males. No difference in fecundity was observed between infected and uninfected females in the YN population and the GX population. In summary, Wolbachia in the HN population was the only strain that could promote the fecundity of infected females.In the HN population, infected adults were significantly shorter lived than uninfected adults. No difference of longevity was observed in comparisons of the infected and uninfected adults in the YN and GX population.To estimate the abundance of Wolbachia, the copy numbers of the wsp gene were measured using quantitative PCR. Five developmental stages of nymphs (first to fifth instars) and adult females and males of 12 stages (1,2,4,6,8,10,12,14,16,18,20,22 days old) in the HN and GX populations were examined. In nymphs, Wolbachia copy numbers significantly increased along with the developmental stage in both the GX and HN populations. In adults, the quantity of Wolbachia decreased with age after adult emergence in the GX population, while the Wolbachia density fluctuated randomly throughout development in the HN population. In addition, we found that the Wolbachia density in nymphs and adults was significantly higher in the HN population than in the GX population.The Hainan population of Nilaparvata lugens was used as material and the amount of Wolbachia in macropters and brachypters of N. lugens were calculated using real-time fluorescent quantitative PCR. It was shown that the Wolbachia load was higher in females than in males and the macropterous females harbored more Wolbachia than brachypterous females. We dissected N. lugens into four parts (head, thorax, abdomen and six legs) and detected the infection density of Wolbachia in each tissues. The highest infection load in the abdomen of adults can be explained by that Wolbachia are often concentrated in the gonads which are in the abdomen. In the somatic tissues, we also found the wide distribution of Wolbachia. The infection density of Wolbachia in the baenosome was higher than in the cephalosome and legs.