Diversity of culturable endophytic bacteria at different developmental stages of Phthorimaea operculella（ Zeller） and its effects on digestion

【Objective】 To clarify the dynamic changes of culturable endophytic bacteria of Phthorimaea operculella（Zeller） with the growth and development of the host and their effects on feeding and digestive function, which could provide theoretical basis for exploring the interaction between symbiotic bacteria and hosts. 【Method】 Taking Phthorimaea operculella（Zeller） at different developmental stages as the research object, the culturable endophytic bacteria were isolated and cultured in the body（eggs, 1^st and 2^nd instar larvae） or intestine（3^rd and 4^th instar larvae, male and female pupae, male and female adults） of Phthorimaea operculella（Zeller） at different developmental stages by traditional isolation and culture technology. The isolated strains were identified by 16S rDNA sequence analysis, through refeeding dominant bacteria and resident bacteria, the nutritive indexes of Phthorimaea operculella（Zeller） were detected by gravimetric method, and effects of dominat bacteria and resident bacteria on the feeding and digestion of Phthorimaea operculella（Zeller） larvae were analyzed.【Result】The composition and diversity of culturable endophytic bacteria at different developmental stages of Phthorimaea operculella（Zeller） were different. The number of culturable endophytic bacteria isolated from eggs was the least, and the number of culturable endophytic bacteria isolated from larvae was the most abundant. With the increase of age, the number of culturable endophytic bacteria gradually increased, and began to decline after pupation. There were 3 phyla, 13 families, 17 genera and 30 species of culturable endophytic bacteria in Phthorimaea operculella（Zeller）. Among them, there were 2 phyla, 3 families, 3 genera and 3 species of culturable endophytic bacteria in eggs. There were 2 phyla, 2 families, 2 genera and 3 species; 2 phyla, 4 families, 5 genera and 6 species; 3 phyla, 9 families, 10 genera and 11 species; 3 phyla, 10 families, 10 genera and 11 species; 3 phyla, 5 families, 5 genera and 7 species; 3 phyla, 8 families, 8 genera and 10 species of culturable endophytic bacteria in 1^st-4^th instar larvae, pupae and adults respectively. The dominant species of endophytic bacteria in Phthorimaea operculella（Zeller） at different developmental stages were different. The dominant species of culturable bacteria of the 1st instar larvae was Enterobacter ludwigii, while the dominant species of culturable bacteria of eggs, 2^nd-4^th instar larvae, pupae, and adults were Enterococcus mundtii. Enterococcus mundtii was stable at all developmental stages of the Phthorimaea operculella（Zeller）, and Serratia rubidaea was found in the 3rd and 4th instar larvae, pupae and adults. Enterococcus mundtii, Enterobacter ludwigii and Serratia rubidaea can promote the digestion of Phthorimaea operculella（Zeller）.【Conclusion】 The species of culturable endophytic bacteria in Phthorimaea operculella（Zeller） are abundant. The composition and structure of culturable endophytic bacteria in Phthorimaea operculella（Zeller） at different developmental stages are different. The species of culturable endophytic bacteria in larvae are greatly higher than those in eggs and pupae, but there is no obvious difference in dominant species. The dominant species of endophytic bacteria can promote the growth and development of the host by promoting the digestion of larvae.