Studies on the nutritional supplement of mulberry leaves with Cowpeas (Vigna unguiculata) to the silk worm Bombyx mori (L) (Lepidoptera: Bombycidae) upon the activities of midgut digestive enzymes

Abstract

Aim : To evaluate the changes in the activities of midgut digestive enzymes activities of silkworm fed with mulberry leaves supplemented with Cowpeas (Vigna unguiculata). Materials and Method: Finely powdered Vigna unguiculata was dissolved in distilled water and diluted to 2.5%, 5%, 7.5%, and 10% concentrations. Fresh mulberry leaves (Morus alba L.) were sprayed by each concentration and were fed to silkworms, from third to fifth instar, five feedings/day. Group 1 larvae received mulberry leaves sprayed with distilled water and served as control, group 2 larvae received 2.5% Vigna unguiculata sprayed mulberry leaves, group 3 larvae received 5% Vigna unguiculata sprayed mulberry leaves, group 4 larvae received 7.5% Vigna unguiculata sprayed mulberry leaves and group 5 larvae received 10% Vigna unguiculata sprayed mulberry leaves. Result: Silkworm larvae fed on Morus alba L. (mulberry) leaves enriched with 7.5% concentrations of Vigna unguiculata, significantly gained more pupa weight, silk length and silk weight as compared to those fed on normal MR 2 mulberry leaves. Hence, 7.5% dose was fixed as an effective dose. Further, same study was conducted to find out the changes in the digestive enzymes activities in the midgut occurred in the fourth day of fourth instar larvae. There was a significant increase in the midgut urease, amylase, sucrase, and protease activities. But midgut trehalase activity was significantly decreased. Conclusions: The results suggest that supplementation of Vigna unguiculata with mulberry leaves at a concentration of 7.5% has enhanced the digestion of ingested food which in turn reflects in the quantity of silk produced.