Cassava whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), in sub-Saharan African farming landscapes: a review of the factors determining abundance

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a pest species complex that causes widespread damage to cassava, a staple food crop for millions of smallholder households in Sub-Saharan Africa. Species in the complex cause direct feeding damage to cassava and are the vectors of multiple plant viruses. Whilst significant work has gone into developing virus-resistant cassava cultivars, there has been little research effort aimed at understanding the ecology of these insect vectors. In this review we critically assess the knowledge base relating to factors that may lead to high population densities of Sub-Saharan African (SSA) Bemisia tabaci species in cassava production landscapes of East Africa. We focus first on empirical studies that have examined biotic or abiotic factors that may lead to high populations. We then identify knowledge gaps that need to be filled to deliver long-term sustainable solutions to manage both the vectors and the viruses that they transmit. We found that whilst many hypotheses have been put forward to explain the increases in abundance witnessed since the early 1990s, there are little available published data and these tend to have been collected in a piecemeal manner. The most critical knowledge gaps identified were: (i) understanding how cassava cultivars and alternative host plants impact B. tabaci population dynamics and its natural enemies; (ii) the impact of natural enemies in terms of reducing the frequency of outbreaks and (iii) the use and management of insecticides to delay or avoid the development of resistance. In addition, there are several fundamental methodologies that need to be developed and deployed in East Africa to address some of the more challenging knowledge gaps

Susceptibility of cassava to Colletotrichum manihotis

Meeting: International Society for Tropical Root Crops. Africa Branch, Triennial Symposium, 2d, 14-19 Aug. 1983, Douala, CMIn IDL-737

Sensibilité du manioc aux atteintes de Collectotrichum manihotis

Réunion: International Society for Tropical Root Crops. Africa Branch, Triennial Symposium, 2d, 14-19 Aug. 1983, Douala, CMDans IDL-638

Stratégies de sélection de variétés résistantes aux principales maladies du Programme national manioc (PRONAM) du Zaïre

Dans IDL-1152

Bark removal for medicinal use predisposes indigenous forest trees to wood degradation in Zambia

Bark harvesting for medicinal purposes has become widespread in Zambia, mainly due to the high levels of poverty among the population. The injury caused to trees leads to wood deterioration as a result of insect damage and fungal infection. This study aimed to ascertain the effects of different bark harvesting practices on the quality of wood of selected indigenous tree species often used as medicinal plants. The bark of these trees, which included Julbernardia paniculata, Isoberlinia angolensis, Brachystegia longifolia, Albizia adianthifolia and Parinari curatellifolia, was removed by (1) stripping bark on the side of the tree facing the sun, (2) on the shaded side of the tree, (3) covering the wound with mud immediately after harvesting, (4) stripping at night and (5) no wounding as control. Wood of J. paniculata and I. angolensis was severely deteriorated, displaying extensive tissue discolouration, increased insect infestation and profuse gum exudation, especially when the wound was not covered with mud. Covering the wound site with mud considerably protected the trees from wood deterioration and insect damage and this constitutes the best and most sustainable bark harvesting prescription for biodiversity conservation. Keywords: Africa, Albizia adianthifolia, bark harvesting, Brachystegia longifolia, Isoberlinia angolensis, Julbernardia paniculata, Parinari curatellifolia, tree wounds, wood deteriorationSouthern Hemisphere Forestry Journal 2007, 69(3): 157–16