Sensibility to Mononychellus tanajoa Bondar (Acari: Tetranychidae) of some cassava (Manihot esculenta Crantz) cultivars and effect of damage on yield loss in the Cameroonian western highlands

摘要

The study of the sensibility towards the green mite Mononychellus tanajoa Bondar of some cassava (Manihot esculenta Crantz) cultivars and the assessment of the effect of damage on the yield losses was carried out in the Western highlands of Cameroon. Four cassava cultivars were used: two local (Dschang and Njombe) and two improved varieties (IITA 8017 and IITA 82516). The results obtained showed that the density (mites number/cm~2 of leaf area) was low during the rainy season and high during the dry season, which means that rains reduce the mite population by washing or lead the mites to death. The highest mean density (3.40 mites/cm~2 of leaf area) was obtained on the local Njombe cultivar which is consequently the most sensitive. On the contrary, the local Dschang cultivar, with the lowest mite density (1.40 mites/cm~2 of leaf area) was the most resistant followed by the IITA 8017 cultivar (1.74 mites/cm~2). The IITA82516 cultivar had a mean density of 2.65 mites/cm~2. Yield losses ranged from36.90 percent for IITA 8017 (1.74 mites/cm~2 and damages level of 2.75) to 58.70 percent for local Dschang (3.40 mites/cm~2 and damages level of 3.84). Local Dschang cultivar (1.40 mites/cm~2 and damage level of 2.96) and IITA 82516 (2.65 mites/cm~2 anddamage level of 2.96) had a yield losse of 38.10 percent and 41.80 percent. The results showed that higher the mite density and damage level are, higher is the yield loss, unless the cultivar is tolerant.