Identification of Semiochemicals for the Control of the West African Cocoa Mealybug

Abstract

Cocoa swollen shoot virus disease (CSSVD) continues to be a huge challenge undermining the full potential of cocoa production in Ghana, with its main host transmitters being mealybugs (Hemiptera: Pseudococcidae). Control measures using conventional spraying regimes have proven ineffective due to ecological and physiological factors, while the use of systemic pesticides face sustainability limitation including high cost, phytotoxicity, residue effects and consumers demand for organic farming practices. To address this, Integrated Pest Management, by the use of natural enemies, specifically parasitoids wasps and predatory flies, that have been identified in colonies of cocoa mealybugs are being explored. However, little is known about the role of semiochemicals from these organisms in mediating behaviours such as locating mates, food sourcing, courtship and oviposition. This study aimed to identify potential semiochemicals influencing the behaviour of natural enemies. Solvent extracts from selected wasp parasitoids and midge predators were tested for their activity in behavioural assays and their chemical compositions were analysed using Gas Chromatography Mass Spectrometry (GC-MS). The results revealed a diverse array of compounds with oxygenated functionalities including alcohols, aldehydes, etc., as well as long-chain hydrocarbons. Three key compounds detected with previously reported pheromonal activity are two methyl-branched alkanes; 2 methylhexacosane and 2-methylnonacosane and a C2 keto compound. Additionally, plant volatiles and mealybugs-derived compounds were found to exhibit kairomonal activity. The results demonstrate that there is both pheromonal and kairomonal activity in freshly emerged parasitoids and parasites (1-2 days old). These findings highlight the potential of developing semiochemical blends to attract and enhance natural enemy populations in cocoa agroecosystems. This would suppress mealybug pests and thus reduce the spread of CSSVD.