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Notes on the African root and tuber scale, Stictococcus vayssierei Richard, a recent reported cassava pest in the BasCongo Province of the Democratic Republic of Congo
Abstract/Description
The African root and tuber scale insect (ARTS)(Stictococcus vayssierei. Richard) has increasingly become a major pest of cassava in the forest areas of the Bas-Fleuve District in the most western province of the Democratic Republic of Congo where it was known since long ago without any noticeable damage on the crop. Surveys conducted in the District indicated that the pest is confined to forest zones. The level of infestations on cassava was shown to be highly influenced by the type of predominant forest vegetations where the cassava fields were established. Scale infestations were high in highly degraded secondary forests where cassava is continuously planted and low in well reconstituted forests, where fields are planted after long fallows. Wild alternative host plants were inventoried in different types of fallows and were identified. These plants are thought to serve as reservoir for S. vayssierei infesting cassava fields planted after long fallows. Furthermore, the impact of S. vayssierei attacks on cassava production was experimentally quantified and revealed a negative effect on the bulking of the storage roots and hence cassava yield. An average root yield reduction of45'/" and 60% was obtained on the tolerant and susceptible variety, respectively. This reduction in root yield could not be attributed to any other cassava constraints as at the time the experiment was conducted, the only differences among plots and between varieties were the experimentally manipulated scale infestation levels. This paper reports on the geographical distribution of S. vayssierei in the province of Bas-Congo, the host plants association, the type of damage on cassava and its effects on cassava yield. The pest has been repoded in other provinces with similar forest agro-ecologies in the country. La Cochenille Africaine des Racines et Tubercules(CART) Stictococcus vayssierei Richard estdevenu un ravageur majeur dans les parties desfor6ts secondaires du district du Bas-Fleuve dansla province du Bas-Congo en R6publiqueD6mocratique du Congo oir cet insecte est connudepuis de longues dates sans pour autant causerdes d6gAts d la culture. Des enqu6tes entreprisesd travers le district avaient indiqu6 que ce ravageurest confine aux seules zones forestidres. Lesniveaux d'infestations sur le manioc 6taient mon-tr6s 6tre fortement influenc6s par les types deforOts pr6dominantes du site ou le champ de man-ioc a 6t6 instal16. Les infestations de la cochenille6taient 6lev6es en for6ts secondaires s6vdrementd6grad6es, ou le manioc est continuellement plan-te, et faibles en for6ts secondaires suffisammentreconstitu6es aprds des longues jachdres. Desplantes h6tes alternatives sauvages 6taient inven-tori6es dans diff6rents types de jachdre et 6taientidentifi6es. Ces plantes hdtes alternatives sontsuppos6es etre des r6servoirs de la cochenilleattaquant le manioc dans les champs install6saprds longues jachdres. En plus, I'impact de S.vayssierei sur la production du manioc avait 6t6exp6rimentalement 6valu6 et avait montr6 un effetn6gatif des attaques tant sur la tub6risation que surle rendement. Une moyenne de 45"h et 60% der6duction sur le rendement 6tait observ6e la vari6t6tol6rante SADISA et la vari6t6 susceptible LUEKI,respectivement. Ce rapport pr6sente et discutequelques r6sultats de recherche sur la distributiong6ographique, les plantes hotes alternatives, lestypes des d6g6ts sur le manioc et aussi l'effet surle rendement. Ce ravageur a 6t6 aussi rapport6dans d'autres provinces du pays ayant des agro-6cologies similaire.