Effect of zinc on the larval growth and quality cocoon parameters of silkworm (Bombyx mori L.): A review

Silkworm is an economic insect producing valuable silk. All insects require a variety of minerals and trace elements as micronutrients. However, caterpillars are known to require appreciable amounts of potassium (8000-9000 ppm DW), phosphate (2000- 6000 ppm), and magnesium (1000 ppm) (Muniandy, 2001). The role of mineral nutrition, more particularly that of Zinc, needs to be ascertained as it is known to play a vital role in the synthesis of lipids, proteins and carbohydrates and in reducing the duration of larval and pupal stages (Bhattacharya and Kaliwal, 2005). Such studies provide substantial evidences for practical application of Zinc and other microelements for qualitative and quantitative improvements in silk production. The cocoon spinning activity is an important phase in the silkworm which produces the cocoons, the final product of the insect. This activity which lasts for 5 to 6 days requires continuous function of the nervous system and the muscular system where the Cholinergic and Glutametargic neurotransmitters play key roles. Since, the larval stage is the only feeding stage in silkworm development, intake of balanced diet is very essential for silk production. By supplementing the diet with minerals, vitamins and trace elements, the various functions of the hormonal system, neuromuscular system, reproductive system etc., can be modulated effectively. Zinc fortified mulberry leaves increases the fecundity of silkmoths after feeding to silkworms and also quality parameters of cocoons like higher shell cocoon ratio, silk-body ratio, raw silk percentage, denier and renditta and secondly it lowers the floss-shell ratio by decreasing the floss protein synthesis.