GUWAHATI, Jan 15 - The complaint being made by silkworm farmers of the State for the past several decades that the use of pesticides in tea gardens and tilling fields in their neighbourhood has been harming their worms and affecting their products, should not be looked down upon as a silly one. The scientific truth behind this complaint has now been found.
The Institute of Advanced Study in Science and Technology (IASST) here has found, through a study, that pesticides do harm silkworms and thus affect the products of silkworm farmers in the long run.
Dr Dipali Devi, Associate Professor in the IASST, who led the study, said that pesticides damage the immune system of the silkworms and alter the physiology which affects the commercial characters of cocoon as well as silk fibres. Intoxication symptoms like body blackening, less feeding and vomiting were observed in silkworm larvae exposed to pesticide along with oozing out of hemolymph (body fluid) as rectal protrusion of the larva within 12 hours of exposure.
It is found that most of the farmers prefer the use of pesticides like endosulfan, quinalphos, chlorpyrifos, monocrotophos, cypermethrin, deltamethrin, profenophos, thiomethoxam, cartap hydrochloride, imidaclorpid, dicofol, ethion, etc. The average pesticide utilisation in the NE region is 6.13 gram per hectare per annum. This value is, however, quite low in comparison to the use pesticide at the national level, which is 600 gram per hectare per annum, Dr Devi said.
These pesticides enter and contaminate the environment either by direct application, spray drifts or crop run-off and shows adverse effect on the non-targeted organisms starting from microorganisms to higher vertebrates, she said.
The IASST scientists undertook the study on the eri silkworms, as indoor rearing of these silkworms is possible, while muga silkworms grow only in the wild. Keen scientific observation on muga silkworms is hence difficult, said Dr Devi. She said Northeast is rich in seri-biodiversity as this region is bestowed with the natural habitat for a number of sericigenous insects and their host plants. Among these, four types, namely, mulberry silkworm Bombyx mori and non-mulberry silkworms namely Oak Tasar Antheraea proileyi, muga silkworm Antheraea assamensis and eri silkworm Philosamia ricini have been commercially exploited.
Silk growers of Lakhimpur and Dhemaji districts are suffering heavy losses and the affected farmers link the cause of this loss to the unchecked use of pesticides in the neighbouring tea gardens, she said.
The study reflects the negative impact of organophosphate and pyrethroid pesticides on eri silkworm and provides a serious apprehension about the potential danger of pesticides to non-target organisms.
This study might be helpful for safe and judicial use of pesticides in agricultural practices as well as in the tea cultivation, so that no serious suffering occurs to the non-target organism like silkworm species for a sustainable growth and development of sericulture industry of this region, said Dr Devi.
Supporting the demand for declaration of a muga endemic zone, she also made an appeal to the authorities concerned to create sericulture zones to protect silkworm races, the unique and precious bio-resources of this region, from such type of human-induced hazards.