A study on the biology and the impact of natural enemies on the African wild silk moth, gonometa sp. at Kamaguti, Uasin Gishu district, Kenya
Ngoka, Boniface M.
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The steadily growing demand for silk in all silk consuming countries provides excellent opportunities for any country to venture into wild silk production. In East Africa, 58 wild silk moth species have been found to occur in three lepidopteran families: Saturniidae, Lasiocampidae and Thaumetopoeidae. In Uasin Gishu district, Gonometa sp. (Lasiocampidae) would be ideal for generation of supplementary income to resource-poor farmers, reduce host plant destruction, promote conservation of the silk moths and at the same time permit positive utilization of these biological resources by the local community. Experiments on the population dynamics of Gonometa species were carried out at Uasin Gishu district using two Acacia plant species (Acacia mearnsii and Acadia hockii). Partial life tables were constructed to evaluate the impact of natural enemies on the population of the Gonometa species. Gonometa sp. caterpillars were found feeding on two abundant host plants namely Acacia mearnsii (Thornless) and Acacia hockii (Thorned). The A. mearnsii maintains green forage throughout the year unlike the A. hockii, which sheds leaves during a dry spell. Thus A. mearnsii could be recommended for mass wild silk cocoon production. The moth's oviposition was bimodal for a year. The moths start emerging during the moths of September-October and the life cycle is completed by moths emerging again during the months of March-April. Moths opted laying eggs on two protected environments (Net sleeves and Plastic containers). The incubation period in the two environments was significantly different at p<0.05 with the plastic containers environment having the shortest period. Larvae had six developmental instars and the larval period was significantly different (P<0.05) between the host plants with the larvae reared on A. mearnsii having the shortest developmental period (72.75±1.83 days). The Gonometa sp., cocoon size and weight varied within the sexes. The female cocoons were larger than the male cocoons with the cocoons mean length and mean width being significantly different at P<0.0001 within the sexes. The pupa had a diapause period in December-February and June-September. Male larvae spun earlier than the female larvae but all moths emerged almost at the same time and mate. The sexual dimorphism exhibited in both pupal and adult stages can be used precisely for identification and separation of sexes during the breeding period. The fecundity of moths kept in the net sleeve environment was higher than that in plastic containers. Eggs in plastic containers had the highest infertility percentage (51.65%). The survival rate observed during the developmental period of Gonometa sp. larvae in this study was higher in the protected than in the unprotected larvae. Disappearance was the key mortality factor. Disappearance covered combined mortality factors that could not be singled out easily especially predators (Birds), escape of the larvae through the net pores and wondering movements of the released larvae.
- MST-Zoological Sciences