Variation of the response of clonal cocoa to attack by cocoa pod borer Conopomorpha cramerella (Lepidoptera: Gracillariidae) in Sabah

Eight cocoa clones were examined for variation in resistance to cocoa pod borer (Conopormorpha cramerella Sn) in Sabah, Malaysia. Over a 13 month period up to 1200 ripe pods of each were shaved back to the sclerotic layer and the number of larval entry and exit holes were counted. There were statistically significant differences in the proportion of larvae that were able to exit, with PBC123, a popular commercial clone in Sabah, and IMC23 is more resistant than BAL244 and KKM22. The six more resistant clones were characterized for pod hardness, using a penetrometer. The correlation with the entry/exit ratio suggested that the measurements could be used for screening clones for resistance. The data indicated that at relatively low rates of infestation, the proportion of larvae that can exit from the pods is negatively correlated with the number that enter, which would amplify the effect of partial resistance. The partial resistance of PBC123 may be sufficient to greatly reduce moth populations in a large enough pure stand of the clone. Pod borer resistance should be given a high weighting in an economic index for cocoa clone selection, and should be combined with tolerance of infestation in the form of low damage to the cocoa beans despite infestation.