Genetic characterisation of an Iflavirus associated with a vomiting disease in the Indian tropical tasar silkworm, Antheraea mylitta.

Antheraea mylitta, the Tropical tasar silkworm, is frequently affected by a vomiting disease called Virosis by sericulturists although not confirmed being of viral origin. Based on the symptoms and the disease pattern, the causal agent is however suspected to be a virus. The condition involves a series of characteristic and progressive symptoms that generally culminates in the death of the larva. The disease is common in autumn season (Sep- Oct), with widespread distribution causing severe damage to the tasar silk industry. The leads for this study were obtained from a transcript identified in the EST database in a different study, which matched the positive strand of Iflavirus, an RNA virus known to infect insects. In the present study the genome of this novel Iflavirus was characterised and the full length of the genome was found to be 9728 nucleotides long encoding for a single large open reading frame (ORF) with flanking NTR regions at 5' and 3' ends and a natural poly A tail at the 3' end. The ORF encoded structural proteins at the N-terminal end and non-structural proteins at the C-terminal end with a predicted 2967 amino acid long polyprotein. The structural proteins consisted of 4 proteins (VP1-VP4) and the non-structural proteins consisted of helicase, RNA-dependent RNA polymerase and 3C-protease. The virus is found in various tissues (midgut, fatbody, trachea, Malpighian tubules and silk gland) and also has a vertical route of transmission, i.e., from gravid females to the offspring. Based on the available data, the virus is a new member of Iflaviridae for which we propose the name Antheraea mylitta Iflavirus (AmIV).

Genetic variation in ecoraces of tropical tasar silkworm, Antheraea mylitta using SSR markers.

The tropical tasar silkworm, Antheraea mylitta, polyphagous sericigenous insect mostly found in the tropical areas of India. It is found in these regions as ecotypes or ecoraces. It feeds primarily on plants, a variety of secondary plants like Terminalia arjuna and T. tomentosa. Tasar culture is a traditional livelihood for lakhs of tribal populace in the areas of Jharkhand, Chhatisgarh, Orissa, Maharashtra, Andhra Pradesh, West Bengal and Uttar Pradesh. In the present study, the genetic diversity of these ecoraces is identified by DNA markers, namely simple sequence repeats (SSRs), most of which produced polymorphic bands.

Estimation of amino acids, urea and uric acid in tasar silkworm, Antheraea mylitta Drury.

The tasar silkworm, Antheraea mylitta Drury, Andhra local ecorace is an exclusive race of Andhra Pradesh. It is on the verge of extinction due to difficulty of acclimatisation at breeding and rearing stages. As an attempt to protect this race, a method of total indoor rearing has been done. In this context, the estimation of free amino acids, excretory products- urea and uric acid were compared during the fourth and fifth instars of tasar silkworm, reared under outdoor and indoor conditions. The study has revealed that amino acids decreased in the fat body in outdoor and indoor reared larvae in contrast to that in the haemolymph where it has gradually increased from first to third crops. This is an important finding as it reveals that indoor worms seem to adopt proteolytic activity in the haemolymph. Secondly, in the fifth instar the excretory products are more compared to fourth instar in the indoor reared worms. During fifth instar, formation of nitrogenous products lessens as silk synthesis enhances. The present study reveals that decrease in uric acid in fifth instar implies increase in growth rate and silk synthesis in both outdoor and indoor worms. The findings of the present investigation is helpful in the conservation and protection of the A. mylitta, Andhra local ecorace.