Hanna, R., Tindo, M., & Goergen, G. 2008 The African root and tuber scale in Central Africa: distribution, hosts, and effects of land use patterns on its abundance.. Proceedings of the XI International Symposium on Scale Insect Studies, Oeiras, Portugal, 24-27 September 2007. ISA Press Lisbon, Portugal 322 pp.

Notes: The African root and tuber scale Stictococcus vayssierei Richard is widely distributed in the Congo Basin of sub-Saharan Africa. This subterranean scale has become a major pest of cassava since it was first identified and described in 1970. The rise in the pest status of S. vayssierei presents an intriguing case study on how a native insect has evolved into a major problem on an exotic crop plant. A major effort is presently underway to identify and characterize biotic, agronomic, and environmental factors that affect scale abundance, and to develop sustainable tactics for scale management on cassava and other affected food crops. Research conducted during the last few years has shed light on some of the factor that may have led to the increase in abundance and damage severity of this scale. Present evidence indicates that S. vayssierei abundance is affected substantially by land use patterns prevalent in the forest zone of Central Africa. Scale densities are higher in cassava fields planted after short fallow than in fields planted after long fallow or after secondary forest. Host plants such as Dioscorea spp. (Dioscoreaceae), Aframomum daniellii (Zingiberaceae), Costus afer (Costaceae), Haummania danckelmanniana (Zingiberaceae), and particularly volunteer cassava were more common in short fallow vegetation compared with long fallow and forest vegetation, and apparently serve as reservoir for S. vayssierei that infest cassava fields planted after the fallow. This knowledge has led to the development of a successful management strategy based on pre-planting removal of host-plants and their residues within the planted fields and in the immediately adjacent vegetation. Scale abundance in cassava fields was also positively related to the degree of disturbed forest cover and to the frequency of occurrence of a closely associated ant, Anoplolepis tenella (Santschi), which is vital for scale survival and dispersal. Several studies are being conducted to develop a fundamental understanding of S. vayssierei and A. tenella ecology for the purpose of developing sustainable tactics to reduce scale infestations on cassava and other economically important host plants.