Tolerance of different host‐plants to the cassava mealybugPhenacoccus manihotiMatile‐Ferrero (Homoptera: Pseudococcidae)

The tolerance of seven varieties of cassava (Manihot esculenta Crantz), Poinsettia (Euphorbia pulcherrima Wild.), Talinum (Talinum triangulare Jacq.) and Faux‐caoutchouc (a hybrid of M. esculenta and M. glaziovii Mull. Arg.) to the cassava mealybug Phenacoccus manihoti Matt. Ferr., was measured in the laboratory, by quantifying morphological and physiological 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 F but did not modify total dry weight, relative growth rate R or net assimilation rate E of plants studied. The decrease in leaf area was extremely variable and depended on plant species and variety. The effect of infestation on dry weight of different 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 the plant species (cassava varieties Ganfo, Incoza and Zanaga were as tolerant as Talinum and Faux‐caoutchouc).