The Ghana Cocoa Board (COCOBOD) approved insecticides, imidacloprid, thiamethoxam and bifenthrin, for the control of cocoa mirids (Hemiptera: Miridae): Implications for insecticide-resistance development in Distantiella theobroma (Dist.) and Sahlbergella
The Ghana Cocoa Board (COCOBOD) in 2001 initiated a national Cocoa Diseases and Pest Control (CODAPEC) programme (popularly known as mass-spraying programme) against the cocoa mirids (Hemiptera: Miridae), which are predominantly Distantiella theobroma (Dist.) and Sahlbergella singularis Hagl. The insecticides approved by COCOBOD for controlling the cocoa mirids under CODAPEC and for individual farmer applications are Confidor® (imidacloprid 200 g/l), Actara® (thiamethoxam 240 g/l) and Akate Master® (bifenthrin 27 g/l). Imidacloprid and thiamethoxam are both neonicotinoid insecticides with cross-resistance between them, while cross-resistance has been established between the neonicotinoids and bifenthrin, a pyrethroid insecticide. Using imidacloprid, thiamethoxam and bifenthrin singly or rotationally selects for genes that confer resistance to the approved insecticides. The detection of ɣ-BHC-resistant D. theobroma in Ghana after widespread use of the insecticide against mirids from the mid 1950s through early 1960s indicated the genetic ability of mirids to develop resistance to insecticides. The mass-spraying of imidacloprid, thiamethoxam or bifenthrin to control mirids is, therefore, increasing selection pressure on field populations of mirids, and escalating the risk of the mirids developing resistance to all three insecticides. Preventing resistance development in the cocoa mirids to the COCOBOD approved insecticides is crucial to avert resistance associated yield losses, reduce the risk of insecticide residues in cocoa beans and safeguards Ghana's foreign exchange earnings from cocoa. Measures for protecting imidacloprid, thiamethoxam and bifenthrin from mirid resistance development are recommended.