Effect of insecticides on Muga silkworm: Study establishes harmful effects of three insecticides used in Assam tea gardens on the golden silk

Common insecticides used in tea-garden areas of Assam have caused tremendous impact on Muga silkworms (Antheraea assamensis).. This has been revealed after a three-year long study conducted by Central Eri Muga Research Training Institute (CEMRTI), Lahdoigarh, Jorhat.

Scientists of the Institute, following a three year long research have identified three commonly used insecticides namely Instant, Atom and Ennova which have severe impact on growth, development and productivity of Muga silkworms.

The study titled “Effect of plant protection formulations on the growth, development and productivity of Muga Silkworm, Antheraea assamensis Helfer (Saturniidae: Lepidoptera)”, described by CEMRI to be the first ever of its kind in Muga silkworm, conducted during 2016-19. Scientists Dr. Kartik Neog and Dr. KH. Subadas Singh led the study.

Of these three insecticide, Instant has the most severe impact on Muga silkworm and even at very low concentrations of less than 0.1 per cent, it causes fatal impact on Muga silkworms. Also, Of these three insecticides, mortality is the highest in case of use of Instant. Fatalities occur with the symptoms of vomiting, total loss of appetite, it states.

The study also reveals that use of Atom insecticide in tea-gardens cause loss of appetite, vomiting, sluggishness, body colour changes and ultimately death of Muga silkworms. At high doses with more than 0.1 per cent use, the effects can be immediate death.

It also states, Ennova and Atom has similar effects on silkworms and the immediate effects are detrimental at higher doses.

However, at lower dose that is less than 0.1 percent, the effects are not immediate and the intensity can be less. Restoration of health, appetite, colour and stability are recorded in the case of Ennova, it states. Loss of colour change or physical changes is not observed in case of Instant, it states.

The objectives of the study includes assessing impact of chemical pesticides and plant protection formulations, assessing impact of biopesticides and biocontrol agents and to develop suitable methodologies and procedures to reduce the adverse impact.

Scientists of the Institute suggest introduction of geospatial technology for identification of various landscape and climatic parameters was crucial for Muga silkworm disease incidence.

CEMRTI Scientists also suggest Muga silkworm rearing should be away from agricultural land, built-up area, factories etc as disease incidence highly correlate with increase in anthropogenic activity. Muga farms surrounded by dense forest area are beneficial for optimal growth of silkworm due to balance in land surface temperature.

One of the key suggestion is that the aspect of the farm must avoid south facing in hot and humid climate as Muga silkworms are shade lovers. Fifteen days average maximum temperature and maximum relative humidity data may be used to predict percent of flacherie infestation with the predicted model developed in the study before 10 days and 5 days of harvest coinciding with 4th and 5th Instars respectively.

Muga silkworm rearing farmers should take proper precautionary measures to avoid disease out-break during the period when temperature exceed 30°C with relative humidity exceeding 80% for few consecutive days.

According to statistis of Central Silk Board, Muga production in Assam during 2017-18 was 192 MT out of a total 31,906 silk production. During 2018-19 it was 233 MT aginst 35,468MT total silk production; during 2019-20 it was 241 MT against 35,820 MT total silk production and during 2020-21 it was 239 MT against 33,770 MT total production.

Despite institutional research and efforts, Muga plantation area has not been increased in the state during this period. According to a report of Central Silk Board titled Functioning of Central Silk Board and Performance of India Silk Industry, published during January, 2020 Muga plantation area of the state during 2018-19 was 233 hectare against a targeted 260 lakh hectare. During 2019-20 it came down to 227 lakh hectare against a targeted 280 lakh hectare.

Photo and text -Ratna Bharali Talukdar