INTRODUCTION

The silkworm Bombyx mori, is a commercially important insect, produces the silk. Akola and Washim district though known as cotton producing districts, farmers in villages, are now encouraged for opting sericulture, taking commercial crops throughout the year, using CSR2 and Kolar gold breeds. However there is great deal of loss every harvest as silkworm is susceptible to a number of diseases during rearing. In tropical countries like India, almost all the major pathogenic microbes infect and cause disease to silkworm (Rajsekhar et al., 1992: Doreswamy et al., 2004).

The most common diseases of silkworm are Grasserie caused by a virus: nuclear polyhedrosis, Flacherie, caused by

ARTICLE INFORMATION:

*Corresponding Author Received 22nd October, 2013

Accepted after revision 20th December, 2013 BBRC Print ISSN: 0974-6455

Online ISSN: 2321-4007

©A Society of Science and Nature Publication, 2013. All rights reserved.

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bacteria: Streptcoccus and Staphylococcus in association with Flacherie virus, Muscardine, Aspergilosis, caused by fungal infection, and Pebrin, a protozoan disease caused by a para- sitic microspor-idian, Nosema bombycis. The diseases prevail throughout the year, and in tropics they are significantly high (Srivastava and Kumar, 2009).

These infections vary seasonally, and greatly affect, the economic performance of these worms. According to Sivapra- kasam and Robindra (1995) commercial silkworm rearing units are to be regularly surveyed for incidence of such diseases. Such surveys were earlier, conducted by Christi and Schaf (1990) in Jammu and Kashimir State, Samson et al., (1990) in Karnataka, Reddy and Rao, (2009) in Andhra Pradesh, and by Isaiarasu et al., (2011), in Virudhunagar district of Tamilnadu. Such study however has not been carried out in Akola and Washim, the new districts on the sericulture map of Vidarbha

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region in Maharashtra. Therefore attempts are being made to know the seasonal silkworm diseases and their incidence lev- els, in the commercial silkworm crops in Akola and Washim districts. The results of the study will make local silk growers aware about the diseases and help them to take due control measures.

MATERIAL AND METHODS

Akola and Washim are districts in the Indian state of Mahar- ashtra, which forms central part of Amravati Division. Washim was earlier a part of Akola. These study districts were surveyed and the information of the leading commercial silk growers located in Wadegoan, Deulgaon, Khanapur, Patur and Balapur in Akola district, Sawad, Kalamba, Risod, Maihsaldoh, Male- goan in Washim district was collected. With due consent of the farmers, a Season wise survey of the silkworm diseases was conducted during the year 2010-11 and 2011-12. All the centers were visited during rainy, winter and summer seasons. At fifth instars larval stage external examination was done, to identify worms infected for Grasserie, Flacherie, Muscardine and others. During every visit, prevailing ambient temperature and humidity was determined and recorded.

RESULTS AND DISCUSSION

The survey in Akola and Washim districts revealed that the common breed of silkworm in the area is dominated by CS 2 and by Kolar gold in summer. The data regarding the seasonal diseases in silkworm occurred during the year 2010-11 and 2011-2012 are presented in Table 1.

The figures revealed that all the major diseases of the silk- worm namely, Grasserie, Flacherie, Muscardine are reported to infect the silkworm in all studied commercial crops from Akola and Washim districts. Same disease pattern has also reported by Reddy and Rao, (2009) in the districts of adjoining state of Andhra Pradesh. Worms infected with Grasserie were sluggish, with swollen inter-segmental region, fragile having easily breakable integument. Flacherie infected larvae were, observed to be dull, lethargic, soft and flaccid was vomiting gut juice, with dysentery and chain type faeces. Muscardine affected larvae were having oil specks on the surface of the integument and later became hard, dry and enclosed into a white or green coloured structure.

As depicted in the table 1, our first survey (2011-12) reported that in rainy season incidence of Flacherie was

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7.0- 9.0%, Grasserie was 6.0 - 9.5% and Muscardine was

0.5- 2.5. In winter season, the Flacherie was 2.0 - 4.0%, Grasserie was 5.0 - 7.0% and Muscardine was 19.0 - 22.0%. While in summer season the Flacherie was 7.0 - 9.0%, Grasserie was 6.0 - 9.5% and Muscardine was lacking.

Survey during 2011 - 12, found that in rainy season Flach- erie was 2.5 - 3.8%, Grasserie was 3.0 - 5.0% and Muscardine was 0.0 - 1.0%,.In winter season Flacherie was 0.0 - 1.0%, Grasserie was 1.5 - 3.6% and Muscardine was nil. In summer season Flacherie was 4.0 - 6.8%, Grasserie was 3.5 - 6.8% and Muscardine was nil.

As per the data, collected during 2010-11and 2011-12 the incidence of Flacherie and Grasserie was higher during rainy and summer season in the studied districts. The reports coincide with that of Etebari et al., (2007) and Chandrasekharan, (2009) who reported similar incidence of Grasserie and Flacherie in the commercial silkworm crops respectively. They claimed that such incidences are caused by greater variations in environ- mental conditions specially, the temperature and water vapors in the atmosphere during these seasons. Srivastava and Kumar, (2009) too mentioned incidences of bacterial Flacherie and cytoplasmic polyhedrosis caused losses up to 48.9 and 35.4 per cent respectively to the commercial silkworm crop growers.

Winter conditions in the region are dry and more suitable for fungal growth; therefore encourage the spread and trans- mission of Muscardine fungus (Miyajima, 1978). Accordingly in the present study too Muscardine infection was reported higher during winter season, but very much reduces during rainy season and lacking in summer.

The table also revealed that, there was reduction in inci- dence of diseases in year, 2011-12 as compared to 2010 2011. It indicated that the incidence of diseases varied not only sea- sonally but also varied from year to year. The reduction in the incidence of diseases reported may be due to the favorable ambient conditions prevailed during 2011-12. Similarly clean- liness drive after harvesting, a more hygienic practice and timely control measure according to Ramesh Babu et al., (2009) and Mahalingam (2010 ) if followed by the growers always reduces the incidence pathogenic diseases in, silkworms . High frequency of infections in commercial crops of silkworms may be due to perseverance of the agents at high concentrations in the silkworm-rearing centers (Ramesh Babu et al., 2009). These pathogens are difficult to devastate and can keep on for long periods under amiable conditions. The agents released by diseased worms easily mount up and spread in the rearing unit through different pathogens. Thus it can be concluded that post harvest cleanliness, good quality mulberry leaves, hygi- enic practices and use of advanced disease resistant breed of

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silkworm help a great deal in protecting the commercial silk- worm crop from the seasonal incidence of Grasserie, Flacherie, and Muscardine in the region.

REFERENCES

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