Systemic Insecticides for Theobroma cacao L., Their Translocation and Persistence in Foliage and Residues in Cacao Beans1

Abstract

From preliminary screening of 14 systemic compounds with cacao seedlings in Costa Rica, Thimet, Chipman R-6200 ( 0,0 -diethyl S-(2-diethylamino)ethyl phosphorothiolate), demeton, Isolan and dimefox were selected for further study. These five systemics were compared on the basis of their translocation and persistence in the foliar parts of mature cacao trees after trunk implantation, their effect on the flavor of chocolate produced from beans from the treated trees, and the level and nature of residues in the beans using radiotracer and anticholinesterase methods of analysis. Thimet and Chipman R-6200 were readily translocated into the foliar portions of cacao trees and persisted for as long as 20 months after a single implantation treatment. Little or no residues were found in the cacao beans at any time after treatment regardless of the pod position on the trees in relation to the site of implantation. Studies with radioactive R-6200 demonstrated a high concentration of phosphorus-containing residues in the cotyledons of the cacao beans but these materials did not partition into chloroform and did not inhibit cholinesterase and therefore cannot be considered as hazardous residues. No off flavors were detected in chocolate from beans harvested from any of the systemic treatments but definite off-flavors were obtained when BHC was used as a foliar spray. The insecticidal efficiency of the systemics was not studied because the insect populations in the treated areas were not adequate for this purpose.