Effect of seasons and larval food plants on the quality of Gonometa postica cocoons
The effect of food plants [Acacia elatior Brenan, A. tortilis (Forssk.) and A. nilotica (L.) Del.] on the development time of Gonometa postica Walker (Lepidoptera: Lasiocampidae) larvae and the quality of their cocoons was studied in the Imba and Mumoni forests of Mwingi, Eastern Kenya, during the long (March-May) and short (October-December) rainy seasons of 2006 and 2007. Larvae were reared in semi-captivity in net sleeves attached to branches of the plants. The period between hatching of eggs and spinning of cocoons, as well as their weight, as determinants of cocoon quality were recorded. In addition, collections of cocoons from the wild were done in the two forests from the same host plants for assessment of their quality. In the cage experiment, larval development period and quality of cocoons differed according to food plants, seasons and sites, whereas quality of cocoons sampled from the wild habitat was similar for all food plants and seasons but varied according to site. Generally, there was a positive correlation between weight of cocoon, its length and width for the two seasons for both the semi-captive population and those from the wild. Larvae reared on A. elatior had a shorter development period and higher cocoon quality than those raised on A. tortilis and A. nilotica. Generally, temperature and relative humidity significantly influenced larval development time and the effect was both positive and negative. Rainfall was generally higher in Mumoni than in Imba. The implications of the above findings for the semi-captive rearing of G. postica to increase the quality of cocoons are discussed.
KeywordsAcacia species Cocoon quality Larval development period Semi-captive rearing
The authors are grateful to the International Fund for Agricultural Development (IFAD), United Nations Development Programme-Global Environmental Fund (UNDP-GEF) and DAAD (German Academic Exchange Service) for providing financial support and to the International Centre of Insect Physiology and Ecology (ICIPE) for providing technical support for this work. We thank Daniel Muia and Florence Kiilu of ICIPE for their assistance in data collection. We express our sincere gratitude to silk farmers in Imba and Mumoni forests of Mwingi, eastern Kenya, for supporting this project. We appreciate the critical views and comments expressed by Dr. Fritz Schulthess on the draft manuscript.
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