BIOLOGICAL-CONTROL OF THE CASSAVA MEALYBUG, PHENACOCCUS-MANIHOTI (HOMOPTERA, PSEUDOCOCCIDAE), IN ZAMBIA

Surveys were carried out in Zambia twice yearly from 1986 to 1990, to assess the impact of a biological control campaign against the cassava mealybug (CM), Phenacoccus manihoti Mat.-Ferr., throughout the infest ed area. From 1984 onward, the exotic parasitoid Epidinocarsis lopezi (De Santis) (Hym., Encyrtidae) and some exotic coccinellid predators w ere released on 54 occasions along the spreading front of CM infestati on. E. lopezi established in every release site, spread, and covered t he entire infested area, but the exotic coccinellids did not establish . Between 1986 and 1990, CM populations declined on average 5.8 times. In a multiple regression analysis involving meteorological, agronomic , plant, and entomological variables, from a total of 4804 cassava fie lds, nine variables had a significant influence on the CM population d ensity, which in turn was the main factor influencing tip damage score s. The duration of E. lopezi's presence in an area was the most import ant factor: in the year the CM was recorded for the first time in a pa rticular district, more than 20% of all cassava fields had an average of 10 or more CM/tip (a few having as many as 1000). This percentage w as gradually reduced to 0% in Year 5. The condition of the plant, its age, rainfall, and water retention capacity of the soil were also impo rtant. Where CM populations were lower, damage by the cassava green mi te, Mononychellus tanajoa (Bondar) (Acari, Tetranychidae), appeared mo re severe. The frequency of ants increased with the CM population dens ity. In conclusion, biological control of the CM in Zambia was success ful. (C) 1994 Academic Press, Inc.