impact of Sahlbergella singularis on the development of young plants of two cocoa varieties in Central Cameroon

In Cameroon, cocoa culture is strongly influenced by mirid attacks in general and by those of the species Sahlbergella singularis in particular. Damages related to this main cocoa pest that feeds as well on fruits as vegetative parts are difficult to quantify. So far, little studies have been done on damages of this species to cocoa varieties. In addition, works focused in damage evaluation of different stages of development of this Heteropterous on different varieties are almost non-existent in Cameroon. A description of the damage young fruits and cherries of two cocoa varieties (Amelonado and Trinitario) associated with the comparison of damage rates S. singularis developmental stages was carried out of in Libelli-Ngoï and the University campus of Yaoundé I from March to september 2017. Artificial infestations of young fruits and cherries were made by cocoa variety and stage of development of S. singularis. Dietary preference was tested using an experimental device consisting of transparent cylindrical boxes in which a fresh cherry (or a fresh greedy) of each cocoa variety was introduced with stage of mirid. S. singularis bites have negatively affect length and leaves number of young fruits on the one hand and on length, diameter and shape of pods on the other hand. When the intensity of the bites is higher, the leaves of young plants and young cocoa fruits turn yellow and dry out. Larva stage L1, L2 and L3 did not have a significant effect on young plants and young fruits mortality. That mortality was more pronounced in the variety Trinitario than Amelonado variety. The L5 larva was the most destructive stage. Dietary preference test has globally shown that S. singularis feeds more on the Amelonado variety than Trinitario The cherries of each variety are more adapted to food needs than the greedy.
Keywords: cocoa, Sahlbergella singularis, variety.