Biodiversity of wild silkmoths (lepidoptera) and their potential for silk production in East Africa
Kioko, Esther N.
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Wild silk production is a unique eco-friendly agro-practice with the potential for environmental amelioration, employment and income generation. The present utilisation of wild silkmoths hardly accounts for 5% of the rich potential and most of the production is from the Far East countries. The steadily growing demand for silk in all consuming countries provides excellent opportunities for any country to venture into wild silk production. In East Africa, wild silk production would be ideal for generation of supplementary income to resource-poor farmers, reducing the destruction of their host plants, promoting conservation of the silkmoths and at the same time permitting positives utilisation of these biology resources by the local community. In Kenya, Uganda and Tanzania, 58 wild silkmoth species of three lepidoptera families, Saturniidae,Lasiocampidae and Thaumetopoeidae were recorded. These species diversity varied in these three families. In family Saturniidae, 19 species were recorded in 6 genera, 33 species in 17 genera in the family Lasiocampidae and 6 species in one genus in family Thaumetopoeidae. Two case studies carried out on the distribution of Bridelia micrantha (Hochst) Bail (Euphorbiaceae) the hostplant of the wild silkmoth Anaphe panda (Boisduval) (Thaumetopoeidae) and Sclerocarya birrea, (A. Rich.) Hochst. (Anacardiaceae) the host plant of the silkmoth Argema minosae (Boisduval)(Saturniidae) revealed that the hostplants are widely distributed in the three East African countries. In western Kenya, a ground survey confirmed the availability of B. micrantha with 84% of the farmers having it in varying numbers in their land. A questionnaire distributed to 50 local farmers near the Kakamega forest responded positively (98%) to the potential of initiating wild silk farming as an extra source of income. Further phenological studies on selected species, Gonometa sp. (Lasiocampidae) at Nguni, Mwingi and A. mimosae at Sultan Hamud, Makueni, Kenya showed that these silkmoths have two generations each year. The adult moth emergence synchronised with the hostplant state, which was also influenced by weather conditions. A high larval mortality of the silkworms of both species was observed in the field. The overall mortality from the first instar to the onset of cocoon spinning for Gonometa sp. reared on caged Acacia elatior Brenan was 82.9% during the short rains of 1996 and 78.9% during the short rains of 1997. In A. mimosae, reared on the hostplant Sclerocarya birrea, 80.6% larval mortality was recorded during the short rains of 1997. Rearing the Gonometa sp. silkworms in net sleeves tied to the hostplant branches reduced the mortality to 23.9% In both species, the pupal stage was the longest indicating the possibility of pupal diapause. Gonometa sp. pupae observed in controlled environmental conditions in an incubator had a significantly shorter life span (87.2 + 3.6 days) compared to those observed under room condition (124.0 + 11.2 days). This is an indication that the pupal diapause in these species can be manipulated for continuous cycle of the silkmoth generations depending on the foodplant state. Predators attacking Gonometa sp. and A. mimosae in the field belonged to three insect ordes, Hemiptera, Orthoptera and hymenoptera. Formicid ants were abundant. Pentatomid bugs of the sub-family Asopinae, Maccroraphis spurcata Walker were observed in Sultan Hamud sucking fluids and killing larvae of A. mimosae. Field collected eggs and cocoons of Gonometa sp. and A. mimosae yielded hymenopteran and dipteran parasitoids. Mesocomys pulchriceps Cameron and Pediobius anastati (Crawford) were identified from the eggs of both silkmoth species. Telenomus sp. and an unidentified Encyrtidae were recorded from Am mimosae eggs. No parasitoids were obtained from A. mimosae cocoons. From Gonometa sp. cocoons, unidentified Tachinidae together with hymenopterans Goryphus sp., Eurytoma sp and unidentified Chalcidoidea were recorded. These parasitoids from the cocoons spoilt the continuity of the silk fiber by making exit holes for the adults to emerge. Cocoons of A. mimosae were not reelable but those of Gonometa sp. gave long filaments of lustrous brown silk. Females gave longer silk thread (706.34 + 222.4 m) compared to males (521.49 + 204.2 m). The mean weight of silk from females was 0.43 + 0.2 g and 0.21 + 0.10 g from males. 2,326 to 4,762 cocoons are required to make one kilogram of Gonometa sp. silk.