Cassava crop yield is reduced by numerous constraints among which African root and tuber scale Stictococcus vayssierei Richard, a devastator of cassava and other crops. This scale damage causes a decrease in amount and quality of cassava tuberous roots in case of serious infestations. It is in this context that a study on influence of the population density African root and tuber scale on cassava (Manihot esculenta CRANTZ) was conducted to determine the damage influence on the yields of two improved varieties and one local variety in different agro-ecological areas of Beni Territory. The objective of this study is to identify among these improved and a local varieties those can be grown in an agro ecological area where the population of african root and tuber scale has no harmful influence on tuberous root yields. To achieve this objective, we verified the hypothesis according to which a good knowledge of the population density helps to determine the rational growing site of cassava varieties. The experiment was conducted in four sites under average altitudes (800-1200 m) and high altitudes (1200-1400 m) with variable infestation rates. The populations of African root and tuber scale with various stages of life and the marketable tuberous root production of each of the varieties as well as climatic factors were determined every three months for two years. The randomized complete block with four repetitions was used. The cluster analysis findings on the effects of the population density of the scale on the yields of these three varieties show that improved varieties were more infested than the local variety under mild altitude. Consequently, their yields were low compared to the local variety. Butamu and Mvuazi improved varieties produced low yields under mild altitudes where there were serious infestations of African root and tuber scale. The yields obtained from these two improved varieties under mild altitudes were respectively 13.1 T/ha and 18.8T/ha compared to Mbayilo local variety that produced 22.5 T/ha at 12 months after plantation (12MAP) on second year screening. Serious infestations of scale under mild altitudes were the cause for low yields of these improved varieties. In high altitude agro ecological areas where the population density of African root and tuber scale was low. Butamu improved variety yielded 25.3 T/ha compared to Mbayilo local variety that produced 37 T/ha at 12MAP on second year of screening. Our results show that the tuberous root production of the released improved varieties of cassava decreases in agro ecological areas with serious infestations of the scale. For the choice of the growing site of the improved varieties, Beni Territory high altitudes with low infestation of African root and tuber scale seem to be better indicated since Mvuazi variety produced 63.8 T/ha.

Cassava is, economically, one of the most important root and tuber crops in Africa. However, its production is compromised by a large number of diseases and pests among which the african root and tuber scale (Stictococcus vayssierei Richard). This insect causes damage that can result in a low yield and non tuber formation of cassava in case of serious infestation. It is in this context that a study on screening cassava (Manihot esculenta CRANTZ) genotypes was carried out for resistance to African root and tuber scale in different agro ecological areas of Beni (North Kivu province, in East of the Democratic Republic of Congo). The objective of the study is to assess resistance to African root and tuber scale of 40 varieties of cassava supplied by the International Institute of Tropical Agriculture and the National Institut of Research Agriculture whose five local are found on the spot after survey. To reach this goal, we verified the hypothesis that stipulates that the introduction of new varieties of cassava in the country is a strategy to fight African root and tuber scale. All varieties were placed in four sites under mild altitudes (1000-1200 m) and high altitudes (1200-1400 m). The populations of African root and tuber scale in various stages of life and the tuberous root production of each variety were assessed every three months for two years in a randomized block experimental with four repetitions. The screening ANOVA findings showed significant effects, S. vayssierei infested the majority of tested varieties. Nevertheless, principal components analysis (PCA) and cluster analysis identified a reconciliation of tolerance vis-