TOLERANCE OF DIFFERENT HOST-PLANTS TO THE CASSAVA MEALYBUG PHENACOCCUS-MANIHOTI MATILE-FERRERO (HOMOPTERA, PSEUDOCOCCIDAE)

The tolerance of seven varieties of cassava (Manihot esculenta Crantz) , Poinsettia (Euphorbia pulcherrima Wild.), Talinum (Talinum triangula re Jacq.) and Faux-caoutchouc (a hybrid of M. esculenta and M. glaziov ii Mull. Arg.) to the cassava mealybug Phenacoccus manihoti Matt. Ferr ., was measured in the laboratory, by quantifying morphological and ph ysiological changes in the growth of plants infested with P. manihoti. A 2-month infestation by 100 mealybugs decreased the total leaf area and the leaf area ratio FBAR. but did not modify total dry weight, rel ative growth rate RBAR or net assimilation rate EBAR of plants studied . The decrease in leaf area was extremely variable and depended on pla nt species and variety. The effect of infestation on dry weight of dif ferent plant organs was not homogeneous, suggesting that translocation of nutrients made during photosynthesis was modified. In cassava the decrease in leaf area, without significant change in leaf dry weight, appeared to be due to physiological changes in plants similar to those induced by water stress. The degree of tolerance was not related to t he plant species (cassava varieties Ganfo, Incoza and Zanaga were as t olerant as Talinum and Faux-caoutchouc).