Effects Of Facultative Endosymbionts Regiellainsecticola On Biological Traits Of The Grain Aphid Sitobion Avenae

Facultative symbionts widely infect aphid populations. They can influence on the capacities of host aphids to use host plant, protect their hosts against natural enemies and to tolerate heat stress. However, the study on the diversity and effects of facultative in the grain aphid Sitobion avenae in Nanjing has been studied rarely. In the present study, we detected the distribution of five common endosymbionts in grain aphid population from March to May,2013 in Nanjing, Jiangsu province, and effects of R. insecticola on life history traits of the grain aphids under different temperatures and population densities. The results were showed as follow:Using diagnostic PCR method, four species of facultative symbionts, Regiella insecticola, Hamiltonella defensa, Rickettsia and Spiroplasma were found in the S. avenae population in Nanjing, China, but a common endosymbiont Serratia symbiotica found in the pea aphid was not found in this population. In the three sampling dates from March to May, the infection of symbionts varied remarkably. The Richettsia and Spiroplasma were predominant, and their infection rates were more than 90%. Infection frequency of R. insecticola and H. defensa in aphids depended strongly on the sampling date. The frequency of R. insecticola decreased from 46.75% to 13.59% between March and May, as well as the frequency of H. defense decreased from 17.59% to 0.97%. Besides, we found that the multiple infection of facultative symbionts was common in S. avenae population in Nanjing, and almost every aphid was infected by Richettsia and Spiroplasma. Furthermore, a superinfection was found in March with four symbionts Regiella, Hamiltonella, Rickettsia and Spiroplasma.R. insecticola was eliminated using antibiotics. A lineage without R. insecticola naturally (Non lineage), a lineage naturally infected R. insecticola (Reg lineage) and a lineage artificially cured the R. insecticola (Amp lineage) were established in laboratory.Under individual rearing at 25℃, the development time, life span and fecundity of three lineages aphids were studied. The results showed that infection of R. insecticola led to a slow development of nymphs, short lifespan and low fecundity of S. avenae. When these aphids were reared by 10,15 and 20 aphids per dish at 25℃, the Reg lineage produced only 45.6%,45.2% and 51.0% of the number of winged offspring as the Amp lineage under the 10 aphids,15 aphids and 20 aphids per dish treatments, respectively. The infection of R. insecticola significantly reduced the ability of S. avenae to produce alate adults. Under group rearing by 10,15 and 20 aphids per dish at 25℃, net reproductive rate (R0) of infected lineage (Reg lineage) was siginificantly lower than that of the cured lineage (Amp lineage) in 15 aphids per dish treatment, and the other life parameters, such as the intrinsic rate of natural increase (rm) and the average generation time (T) had no significant difference among the lineages whether infected by R. insecticola or not.When these aphids exposed to 28℃ and 31℃ for 4h per day, the rate of winged aphids, net reproductive rate, the average generation time and intrinsic rate of natural increase of the three lineages were studied, the results showed that the Reg lineage produced 61.5%, 53.8% and 76.2% of the number of winged offspring as the Amp lineage in the 10 aphids, 15 aphids and 20 aphids per dish treatments, respectively, when these aphids exposed to 28 ℃ for 4h per day. Under the heat shock at 31℃ for 4h per day, the Reg lineage produced 42.0%,89.7%,71.2% of the winged offspring as the Amp lineage in the 10 ahpids,15 aphids and 20 aphids per dish treatments, respectively. There was no significant difference beween Non lineage and Amp lineage.Under heat shock at 28℃ for 4h per day, all life table parameters showed no significant difference beween Reg lineage and Amp lineage. When the three lineages of aphids were exposed to 31℃ for 4h per day, however, survival rate in Reg lineage was significantly lower than that in Amp lineage or Reg lineage under all aphid densities. Under the density 20 aphids per dish, net reproductive rate (R0) and intrinsic rate of natural increase (rm) in Reg lineage were significantly lower than in Amp lineage or Reg lineage. The average generation times (T) among the three lineages were not different in each density, respectively. These results indicated that the infection of R. insecticola caused adverse effects on the fitness of grain aphids under inappropriate conditions, such as the heat shock and high populaiton density.