Studyies On The Functions Of Three Facultative Bacterial Endosymbionts In Sitobion Avenae

Several facultative endosymbionts have been detected in Sitobion avenae(Fab.), and they may have significant impacts on the biological and ecological characteristics of this aphid. The study was focused on three facultative bacterial endosymbionts of S. avenae, including T-type(Hamiltonella defensa), U-type(Regiella insecticola) and Rickettsia sp.. The impacts of these endosymbionts on the fitness of S. avenae clones on five different host plants were evaluated, as well as their effects on the resistance of this aphid to the parasitioid Aphidius gifuensis. The main findings are as follows:1. The fitness of S. avenae clones was evaluated in terms of developmental times and 10 d fecundities. It was found that symbionts U9 and T8 reduced the fitness of S. avenae but symbionts U14, T10, Ric5 and Ric10 increased S. avenae’s fitness on AK58. On wheat PIG, symbionts U7, U9, T7 and T8 reduced the fitness of S. avenae but symbionts Ric3 and Ric10 increased its fitness. On wheat 186, symbionts U11 and T9 reduced the fitness of S. avenae but symbionts Ric1 increased its fitness. On oat, symbionts U11 and T9 reduced the fitness of S. avenae but symbionts Ric3 increased its fitness. On rye, symbionts U7, T7 and Ric2 reduced the fitness of S. avenae.2. Overall, compared with the life-history of corresponding aphid clones that were free of secondary endosymbionts, aphid clones with Regiella insecticola had longer nymphal developmental times on oat and rye, and lower fecundity on rye, so R. insecticola could reduce the fitness of S. avenae on oat or rye. Hamiltonella defensa and Rickettsia sp. appeared to have no significant impacts on the fitness of S. avenae on the five host plants tested. 3. Parasitization rates of aphid clones carrying H. defensa(T2, 28%) by Aphidius gifuensis were significantly different from those of aphid clones with H. defensa eliminated(NT2, 56%). Significant differences were also found for the parasitization rates between Ric3(1%) and NRic3(23%), and between U14(63%)and NU14(48%). Thus, compared with aphid clones free of facultative symbionts, aphids with H. defense and Rickettsia could show reduced parasitization rates, but Regiella insecticola might increase the parasitization by A. gifuensis.