Distribution and abundance of cassava pests in Tanzania with a note on the spiralling whitefly

Two surveys were conducted in Tanzania in May- June 2003 and June-August 2004 to determine the incidence and severity of several cassava arthropod pests including cassava green mite, cassava mealybug, spiralling whitefly, Bemisia spp., cassava scale, red mite, Zonocerus elegans, and several species of termites. Cassava green mite densities were relatively low except in the Lake region in 2004. The introduced phytoseiid predator of cassava green mite Typhlodromalus aripo was found in all regions, with the highest abundance in the Eastern and Lake regions in 2003, and in the Eastern region in 2004. Cassava mealybug infestations were very low throughout the surveyed regions, while B. tabaci (probably in mixed infestations with B. afer) were found in all regions but never exceeding 5 nymphs per leaf. Termite damage was widespread but impact on plant growth and yield is not known. Cassava scale was found only in few fields in the Southern Highlands, Lake and Eastern regions, with damage severity ranging from 2 to 4 (on a scale of 1 to 5). The spiralling whitefly Aleurodicus dispersus, first recorded in Zanzibar in 2002, was found for the first time on the mainland, but only in the Eastern region and at low infestation levels

Biological control of cassava green mite in Tanzania

The cassava green mite Mononychellus tanajoa (Bondar) (Acari: Tetranychidae) is one of the most important pests of cassava, a main staple food crop in Tanzania. The International Institute of Tropical Agriculture (ETA) in collaboration with the Tanzania National Biological Control P r o m (NBCP) launched in 1998 the biological control campaign against cassava green mite in Tanzania with the release of the neotropicd phytoseiid predator Z)phlodromallus aripo DeLeon (Acari: Phytoseiidae), which had proven to be an efficient biological control agent of the cassava green mite in West Mca. The campaign consisted of new introductions and redistributions of I: aripo from infested cassava shoot tips, follow-up surveys to determine establishment, spread, and impact, as well as extension and farmer training on pest and natural enemy recognition and means of enhancing predator efficacy. ~phlodromallusa ripo was h t fo und in March 1998 in the Tanga region, most likely invading h m the southern Kenya coast where it was released in 1996. Subsequently, the Tanzania NBCP in close collaboration with IITA has carried out numerous introductions and redistributions of the predator. Surveys conducted in the following 6 years revealed success M establishment, persistence and spread in five agro-ecological zones including the Lalce (Mars and Kagera regions, except parts of Mwanza region), Western (Kigorna region except Shinyanga region), Southern Highlands (Mbeya and Iringa region), Eastem (Tanga and Coast regions) and Southern (Lindi and Mtwara regions) zones. Up to 2005, there was still no T. arip in parts of 3 regions: Mwanza, Shinyanga and Ruvuma. Cassava green mite mean densities have declined to low levels (less than 20 actives per leaf) in all regions where 'I: a r b has been present. In on-fm impact assessment trial, 'I: aripo was capable of reducing population density of cassava green mite by 64.3% and increasing total and marketable cassava root weights by 61.2% and 71.7%, respectively. There was also a significant increase in total number of roots (25.4%), number of marketable roots (45.78%), stem weights (47.39%), and leaf weight (40.7%) where T, aripo was not eliminated. This report present evidence of the impact of biological control on cassava green mite populations and cassava yield in Tam&, and recommends the use of exotic isolates of the fungal pathogen Neozygites tanajoae, which has been established in West Africa, as a complementary alternative approach in controlling further the cassava green mite in the remaining spots of high infestations