By: Ritah Elit

Introducing silk

Silkworm is one of the most important domesticated insects, which produces luxuriant silk thread in the form of cocoon by consuming mulberry leaves during larval period.

Sericulture entails the production of silk by rearing of silkwormswith the aim of producing silk yarns for silk textiles. Silk is called the queen of textiles due to its glittering luster, softness, elegance, durability, and tensile properties and was allegedly discovered in China between 2600 and 2700 BC. Silk originating in the spittle of an insect is a natural fibrous substance and is obtained from pupal nests or cocoons spun by larvae known as silkworm. The silk is preferred over all other types of fibres due to its remarkable properties like water absorbency, heat resistance, dyeing efficiency, and luster.

Influence of Climate on Silkworm Rearing (Bombyx mori L.)

From a research by TRIDI team led by Clet Wandui Masiga (PhD) and Mr. Ssemugenze Brian, the growth and development of silkworm is greatly influenced by environmental conditions. The biological as well as cocoon-related characters are influenced by ambient temperature, rearing seasons, quality mulberry leaf, and genetic constitution of silkworm strains. Different seasons affect the performance of Bombyx mori L. The seasonal differences in the environmental components considerably affect the genotypic expression in the form of phenotypic output such as cocoon weight, shell weight, and cocoon shell ratio. The variations in the environmental conditions during the last decade emphasize the need of management of the temperature and relative humidity for sustainable cocoon production.

In TRIDI’s findings,the mulberry silkworm (Bombyx mori L.) is very delicate, highly sensitive to environmental fluctuations, and unable to survive extreme natural fluctuation in temperature and humidity because of their long years of domestication since 5000 years. Thus, the adaptability to environmental conditions of the silkworm is quite different from that of wild silkworm and other insects. Temperature, humidity, air circulation, gases, light, and so forth, show a significant interaction in their effect on the physiology of silkworm depending upon the combination of factors and developmental stages affecting growth, development, productivity, and quality of silk.

According to Clet Wandui Masiga (PhD), Mr. Ssemugenze Brian, et al, the seasonal differences in the environmental components considerably affect the genotypic expression in the form of phenotypic output of silkworm crop such as cocoon weight, shell weight, and cocoon shell ratio. The variations in the environmental conditions day to day and season to season emphasize the need of management of temperature and relative humidity for sustainable cocoon production. Temperature and humidity do greatly affect the growth and development of silkworm including recent studies by TRIDI on heat shock protein. It has been discovered that the influence of air and light on silkworm development is very great. In addition to this, emphasis is put on the role of various environmental factors on embryonic development of silkworm egg, nutritional indices of silkworm larva and reproductive potential of silkworm moth. Also highlighted is the caution required during silkworm spinning and influence of temperature and humidity on post-cocoon parameters of silkworm.

Clet Wandui Masiga (PhD), Mr. Ssemugenze Brian, et al further emphasize that; factors that mainly influence the physiology of insects are temperature and humidity despite wide fluctuations in their surroundings, insects show a remarkable range of adaptations to fluctuating environmental conditions and maintain their internal temperature and water content within tolerable limits. Adaptation is a complex and dynamic state that widely differs from species to species. Surviving under changing environment in insects depends on dispersal, habitat selection, habitat modification, relationship with water, resistance to cold, diapause and developmental rate, sensitivity to environmental signals, and syntheses of variety of cryoprotectant molecules.

Clet Wandui Masiga (PhD) intimated that; Uganda is endowed with the most favorable climate in the world suitable for all sericulture practices thus conducive enough for the rearing of these multivoltine × bivoltine hybrid silkworms. This explains why all the National Sericulture Resources Research Centers and stations in all regions of Uganda are doing well irrespective of the weather condition and season.

Summarily, Mulberry thrives under various climatic conditions ranging from temperate to tropical located north of the equator between 28° N and 55°N latitude. The ideal range of temperature is from 24 to 28°C. Mulberry grows well in places with an annual rainfall ranging from 600 to 2 500 mm. Everbearing mulberry trees grow in Zones 5-10—across most of the country.

They are able to tolerate cool and hot temperatures, and they are fairly drought-tolerant. Under ideal conditions (78° to 88° F and allowed to feed nearly continuously) silkworms can go from egg to 1 inch in length in about 12 days, and 3 inches in under 30 days. The worms will begin to spin cocoons at about 28 - 30 days old or when they are between 2 1/2 and 3 inches long.Dark condition, room temperature and 65% RH is required for incubation of silkworm eggs. 27-28 °C and 80-85% RH is required for first and second instar larvae (Chawki silkworm rearing), while 24-25 °C and 60-65% RH is required for third, fourth and fifth instar larvae (late-age silkworm rearing). Mulberry trees are quite drought-tolerant and cold-hardy, and many varieties grow in poor soil. In some areas, they're even known as “weed trees” because they show up uninvited in neglected areas.”. Mr. Ssemugenze Brian concluded.

 Tropical Institute Of Development Innovations (TRIDI) is pioneering all sericulture value chains in the whole of East Africa in over 26 districts and aver 28 stations countrywide.

 These centrers and or stations include; Kween, Sheema, Mbarara, Kiruhura, Bulambuli, Kamuli, Mubende, Gomba,  Mukono, Iganga, Luweero, Kayunga, Nakaseke, Nakasongola, Kween, Bukedea, Zombo, Nwoya, Buikwe, Pallisa, Busia (on a total of 627.92 acres). Silkworm rearing has so far been carried out in 6 districts i.e. Sheema, Mukono, Kamuli, Pallisa, Iganga and Kayunga, Zombo, Bulambuli. The newly established demonstration farms are in; Lira, Adwila,  Amolatar and Otuke districts. Sericulture is currently employing about 1,000 people with 99% of the total population being Ugandans most especially, local communities.