The Gut Bacterial Composition And Diversity Of Sawfly Acantholyda Posticalis Matsumura

It has been well known that a large and varied microbial community inhabited in the insect gut. These microorganisms play an important role in coevolution between herbivorous insects and their host plants. The microbiota provide the essential nutrients with herbivorous insects, and also have the functions including digestion of plant polymers and detoxification of plant-produced toxins. It is reported that pine needles not only provide insects with the abundant chlorophyll, crude protein, crude fat, vitamins and minerals, but also have several kinds of peculiar chemical components such as resins, tannins and terpenes against insect feeding. Sawflies of Hymenoptera are important leaf-eating pests of confier and broadleaved trees. Most of sawfly species are strong host specific and oligophagous.In order to reveal host-plant selection and adaptation of sawfly species from the view of gut microbiology, the composition of the bacterial communities in different life stages of the pine sawfly Acantholyda posticalis Matsumura were investigated using culture-dependent and PCR-denaturing gradient gel electrophoresis(DGGE) methods. The bacterial communities from larvae of three kinds of herbivorous sawflies, named Nematus hequensis Xiao, Pristiphora erichsonii(Hartig) and Acantholyda posticalis, were also profiled, in order to provide the basic information for host-plant selection and adaptation of herbivorous insects. The results are as follows:1. Seven cultured bacterial strains were isolated from the guts of larval and adult samples of A. posticalis using Luria–Bertani agar medium, and no bacterium was obtained from egg and pupal samples. The sequences blasting results showed these seven strains belonged to Proteobacteria and Firmicutes. Acinetobacter sp., Bacillus spp. and Pantoea sp. were found in adults. Acinetobacter calcoaceticus and Janthinobacterium sp. were distributed at the larval stage.2. The gut bacteria of different development stages from A. posticalis were detected by PCR-DGGE analysis and 30 DGGE bands were found from five samples. The distribution of gut bacteria and DGGE bands among different life stages of A. posticalis was significantly different. The sequecnce blasting results showed that the detected bacteria belonged to Proteobacteria and Firmicutes and Deinococcus-Thermus, including 11 genus and 4 other unknown species. The genus Erwinia was the most widely distributed in the egg sample, while Pantoea spp. predominated in the guts of larvae. In pupae, Band-17 was the brightest and predominant bacterial species, but it is unknown taxon yet. Pseudomonas and Wolbachia endosymbiont were the dominant genera in female and male adults.3. Gut bacteria in three kinds of sawfly larvae were detected by PCR-DGGE and 24 DGGE bands were found from nine samples. Sequence alignment analysis showed that these bacteria mainly belonged to Proteobacteria, Firmicutes, Actinobacteria, and Tenericutes. N. hequensis contained the highest bacterial diversity, followed by A. posticalis and P. erichsonii. In eight detected genera of N. hequensis, Serratia and Rhizobium were the most abundant genera. Six genera were identified in P. erichsonii that was dominated by Enterobacter and Pseudomonas. The bacterial flora of A. posticali was dominated by Wolbachia and Pseudomonas, while other five genera were detected in low abundance. The gut bacterial community in N. hequensis which feed on leaves of willow trees was clearly different from those in two sawflies(P. erichsonii and A. posticalis) feeding on pine needles, both of which showed more similarity in gut bacterial community. The bacterial structures of three kinds of sawflies bear high host specificity.