Survey of Wild Silkmoth Populations in Three Ecological Zones and Evaluation of the Performance of Bobyx Mori L. (Lepidoptera Bombycidae) on three Mulberry Varieties in Ghana

Abstract

The majority of the world’s silk is mulberry obtained from the domesticated silkworm, Bombyx mori L. (Lepidoptera: Bombycidae) with wild silk being minimal. A survey was undertaken in three agro-ecological zones in Ghana to document the wild silkmoth populations and their host plants. In addition, the effect of three mulberry varieties; Mysore local, Kanva 2 and S36 on the performance of five B. mori L. strains; G2xV2xH1xKK, M2xN2xSN1xI1, Z/Y, ICIPE I and ICIPE II was evaluated in the Coastal Savanna agro- ecological zone of Ghana. One hundred and fifty newly emerged silkworms strains were fed on cut leaves of the different mulberry varieties in wooden trays in the laboratory under ambient conditions. Performance was assessed on the basis of measurement of larval developmental time, larval size and weight, cocoon size and weight, pupal and shell weight, and shell ratio. Consumption and utilization of mulberry leaves by the 5 th instar silkworm strains as well as the quality of the raw silk from cocoons were also assessed. The survey found the African wild silkmoth, Gonometa sp. (Lepidoptera: Lasiocampidae) on Acacia sp. in Northern Ghana, and wild silkmoths belonging to this genus is known to produce cocoons of good quality for commercial silk production. Results on the mulberry silk production revealed that the interaction between silkworm strains and mulberry varieties was found to be significant for larval, cocoon, pupal and shell weight, and shell ratio. M2 strain exhibited the longest larval developmental time (23.17 days) while ICIPE 1 had the shortest (21.00 days). Z/Y strain obtained the longest and the widest larvae of (5.09 cm, 0.72 cm) and cocoon (3.25 cm, 1.73 cm) when fed with Mysore local mulberry variety. But in terms of larval, cocoon, pupal and shell weights, Z/Y and M2 strains performed better when fed on K2 and S36 mulberry varieties. In terms of raw silk yield, this study has revealed that the three silkworm strains from Bulgaria (Z/Y, G2 and M2) yielded higher than the two silkworm strains (ICIPE 1 and ICIPE 2) from Kenya. However, ICIPE 1 strain had the highest tenacity and elongation percentage of (4.98 g/d, 21.33 %) raw silk when fed on Mysore local variety and was ideal for silk production but the increase in larval mortality was a major setback. ICIPE 1 silkworm strain obtained the longest filament of 982.13 ± 57.75 m followed by G2 894.38 ± 57.09 m when the larvae fed on S36 food plants. From the study, Z/Y, M2 and G2 were the most suitable silkworm strains in terms of cocoon yield, shell ratio and filament length and could be promoted in Ghana. The silkworms reared on S36 and K2 revealed good growth and development of the larvae, cocoon shell weight, shell ratio and raw silk quality and so its cultivation and use should be encouraged in the production areas. The semi-captive rearing technique could be used to augment the wild population of Gonometa sp. in order to exploit its full potential for commercial wild silk production in Ghana.