INTRODUCTION
The North eastern region of India is home to a number of wild sericigenous insects and is centre of wild silk culture including muga, eri, oak tasar, and mulberry silk (Lokeshwari & Shantibala, 2010). Tasar silk industry has lot of socio-cultural and traditional linkages in India since immemorial and plays a vital role on rural economy and hence indicates its impact on the county’s economy simultaneously with agriculture(Reddy, 2010).The oak tasar silkworm, Antheraea proylei J, is an economically important silkworm of Manipur reared for the production of tasar silk. It is interbred between the male Indian species of A. proylei with the female of Chinese species ofA. pernyii G(Jolly, 1969).The yield and quality of tasar silk cocoons are depended on the climatic conditions, silkworm health and nutrient absorption. Physiology and pathology of the silkworm’s digestion, absorption, nutrient utilization and diseases emergence of the silkworm was closely related to microbiota of the larvae’s midgut. Till date, there are no silkworm races at present, which are deemed as totally resistant to diseases or pests. At the end of the larval stage, silk productions are aided by silk glands whose infection affects silk production, resulting in substantial economic losses to the farmers and industries(Brancalhão, Torquato, & Fernandez, 2009).As disease infected silkworms fail to spin cocoons, analysis of cytological damages in the silk gland is essential. Some histopathological studies showed the susceptibility of silk gland cells to BmNPV (Brancalhão et al., 2009; Khurad, Mahulikar, Rathod, & Rai, 2005; Rahman & Gopinathan, 2004). Hence knowledge of the microfloral changes of the gut in diseased conditions will help in understanding the health and nutrition of the silkworm(Yuan, Lan, Yang, Xiao, & Zhou, 2006)and give us ideas of management to improve the diseased condition during infection as such.
The intestinal tract microflora plays an important role in the health of the host by maintaining a normal ecological balance, regulating absorption, digestion, and assimilation (Jeon et al., 2011). Gut microflora are required in pheromone production, pesticide degradation and survivability, vitamin synthesis, and immunity against pathogens(Reeson, Jankovic, Kasper, Rogers, & Austin, 2003).In addition, these bacteria also resist and compete with the invading microbes and their propagation and strengthen the immune system (Tokuda, Watanabe, Matsumoto, & Noda, 1997). Microbial pathogens infect all animal species leading to disease and death. But their immune defence system helps in protection and survival(Miyashita, Kizaki, Kawasaki, Sekimizu, & Kaito, 2014). Insects especially their larval forms are more susceptible to pathogenic bacterial diseases and their virulence factors than vertebrates which further leads to alteration in host defense mechanism (Waterfield, Daborn, & Ffrench‐Constant, 2004).Culture studies in laboratory conditions of insect gut bacterial communities do not reflect the entire microbial types and strains (Gilliam, 1997). Culture dependent methods screen only a few predominant bacteria genera and are unable to detect bacterial genera with low abundance. The 16S rRNA gene is often used as a marker for identifying the diversity of bacterial species in insect gut microbiota (Reeson et al., 2003). It is of notable fact that gut microbiota is involved in regulating the growth, development and environmental adaptation in the host.
However, information on the gut bacterial communities of many insects, including A. proylei is limited. The molecular information regarding this economically important silk moth remains severely limited till date and only a handful of DNA sequences are available (Shantibala, Devi, Lokeshwari, Anju, & Luikham, 2018; Yang et al., 2019). Additionally, very little is known about the effects of pathogens, its nutrient utilization and disease emergence of silkworm in its gut microbiota. Therefore research of the gut microbiota is of great importance .Little is known about the bacteria inhabiting the gut of this silk moth and even basic information on the insect’s microbial symbionts is lacking. To date, there is no report on profiling of gut microflora in silkworm. Hence, in this present study, we aimed to compare the intestinal microflora of A. proylei of normal and Tiger band disease infected fifth instar larva reared under the same conditions using 16S rRNA‐based sequencing method. Furthermore, we also assess the histopathological changes in the midgut and silk glands after infection to assess the tissue damages. Therefore, our study might provide insights for improvement and management of disease as a step towards conservation of wild seri biodiversity for ecological balance and for sustainable economic viability.