PERFORMANCE OF Bombyx mori (L) AND Samia cynthia ricini SILKWORMS UNDER CONTROLLED ENVIRONMENTAL CONDITIONS IN UASIN GISHU COUNTY

Abstract

The domesticated silkworm, Bombyx mori and Eri worm, Samia cynthia ricini are bivoltine and multivoltine, feeding exclusively on mulberry and castor leaves, respectively. The mature larvae of these silkworms forms a runny fluid before spinning a cocoon, the raw material for the production of silk used in textile industry. Domesticated silkworms are highly sensitive to environmental fluctuations, hindering their adaptability as compared to the wild silkworm. In Uasin Gishu County, temperatures range between 8.40C and 270C which are not suitable for the hatching and rearing of silkworm. The research determined the rearing structures and conditions suitable for silkworm production in Uasin Gishu by constructing Structures with equal dimensions (4mx4mx3m height) with iron roofs as follows; timber walled (L1) and mud walled (L2). Greenhouses with four flaps open (L3), three sides open (L4), two sides open (L5), one side open (L6) and completely enclosed (L7), further concrete walled (L0) structures was also used. A thermo-incubator was used as a control to test hatchability while survival percentage, larval duration to cocooning and cocoon quality and quantity were tested from all the structures. To test for hatchability, 300 eggs replicated three times were hatched in each experimental structure. The temperature and relative humidity were recorded using hygrometer/thermometer, while the duration to an end to every instar and survival was recorded. Similarly, the quality and quantity of cocoons from each structure was determined and compared using convectional parameters. The mean temperature of tested structures during hatching ranged between 23.90C±1.9 in L0 and 30.30C±1.7 in L7, the mean relative humidity of 29.9%±3.9 (L4) and 41.6%±11.6 (L2) was statistically significant in all of them. The time to complete hatching ranged from 3 days in L0 and L4 to 6 days in L1 and L2. The highest percent hatching was 88.8% and 89.5% for B. mori and Eri respectively in L1 but, was lowest in L4. The mean temperature of tested structures during rearing ranged between 22.70C±1.9 in L0 and 31.60C±0.8 in L7 during the wet season while in dry season, the mean relative humidity of 33.3%±7.3 (L1) and 43.2%±9.5 (L0) during wet season and 33.1%±7.3 (L1) and 42.2%±7.4 (L7) was statistically significant (p=0.0001). Larval duration (45.67 days) was longest in L2 for B. mori and 39.67 days for Eri in L2 during the wet season,in dry season the longest duration (38.5 days) in L0 and shortest in L5 (27.5 days) for B. mori whereas, Eri had shortest duration in L5 (21.33 days) and longest in L2 (30.3 days). Larval survival (%) was highest in L2 (76.7±4.2) and L0 (78.7%) during the wet and dry season respectively. For Eri, a similar trend obtained in L2 (77.0%) and L0 (80.1%) in wet and dry seasons respectively. The cocoon weight was highest in worms reared in structure L2 (0.86±0.0) and L5 (0.86±0.1) during the dry season while, L5 (2.78±4.3) was the highest during the wet season. Further, L0 (0.82±0.0) and L4 (1.44±0.4) recorded the lowest cocoon weights during the dry and wet season respectively. Eri cocoon weight was highest in L0 (2.35±0.5) and lowest in L3 (1.82±0.4) during the wet season and highest in L3 (2.44±0.3) and lowest in L4 (1.79±0.5) in the dry season. For B. mori during the wet season the longest Filament length was in L2 (1377.8±150.2) m while, the shortest was from L4 (1292.10±84.1) m which was significantly different. In season two, L3 (1382.8±117.2) m was the longest, while the shortest was from L5 (1137.8±105.4) m and was significantly different. From the Eri cocoon during the wet season the longest filament length was from L2 (437.6±32.3) with shortest in structure L5 (397.6±46.9), with similar trend in the dry season. The seasons did not influence average filament length and weights from the tested structures. These results indicate that hatching of silkworm eggs and rearing can be done in a mud walled structures or in a semi enclosed greenhouse or in a concrete walled structure which can produce high quantity of good quality cocoons in Uasin Gishu County.