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.