1. Lab. of General Biology, Dep. of Animal Biology and Physiology, Faculty of Science; Univ. of Yaounde I; P.O. Box 812 Cameroon
2. Institute of Environmental Research (INFU), Univ. of Dortmund; Otto-Hahn-Str. 6 D-44221 Dortmund Germany
3. Institute of Agric. Research for Development (IRAD); P.O. Box 8367 Yaounde Cameroon