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Behavioural responses of cocoa mirids, Sahlbergella singularis Hagl and Distantiella theobroma Dist. (Heteroptera: Miridae), to sex pheromones.

Behavioural responses of cocoa mirids, Sahlbergella singularis Hagl and Distantiella theobroma Dist. (Heteroptera: Miridae), to sex pheromones.

Sarfo, Joseph Easmon (2013) Behavioural responses of cocoa mirids, Sahlbergella singularis Hagl and Distantiella theobroma Dist. (Heteroptera: Miridae), to sex pheromones. PhD thesis, University of Greenwich.

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Abstract

The mirids, Sahlbergella singularis Hagl and Distantiella theobroma (Dist) (Heteroptera: Miridae), are major insect pests of cocoa, a valuable crop in West Africa. Their control by the application of insecticides is problematic in terms of safety and cost. Therefore, this study was undertaken to determine the potential for use of mirid sex pheromone trapping as an alternative, environmentally-acceptable method of managing the mirids. Based on the behavioural responses of the mirids to pheromones in traps, parameters were standardised for efficient performance of the traps. A range of five blends of the synthetic pheromone, the diester, hexyl (R)-3-
((E)-2-butenoyl)-butyrate and the monoester, hexyl (R)-3-hydroxybutyrate, impregnated in polyethylene vials were assayed with a blank control. Blends of 1000:500 μg and 1000:1000 μg respectively attracted significantly higher numbers of male S. singularis than other blends and the lure attracted male mirids optimally for four weeks with minimal reduction in eight weeks. Field bioassays were conducted to determine the appropriate trap design for pheromone trapping from four models; 2.5 litre and 4.5 litre plastic water bottles, sticky plastic plates, cylinder and standard rectangular traps. All models were equally effective. A field experiment was conducted with sticky glue on the outside of the traps. Combined inside and outside surfaces caught more mirids than the inside surface alone which caught only about 23% of the male mirids. Three field experiments using two different experimental designs were conducted to determine optimal height for trap placement. Traps placed inside the canopy attracted significantly more mirids than below 2.7 m height from the ground. The potential for mass trapping of mirids as a method of control was studied through three mass trapping experiments on research plantations and smallholder farmers’ farms. Catches of male S. singularis in pheromone traps were significantly reduced in mass-trapped fields but pheromone trapping did not control mirid numbers or affect damage on cocoa. Densities of 150 and 230 traps/ha were found to be optimal for trapping S. sahlbergella and D. theobroma respectively. Catches of male S. singularis in pheromone traps, however, predicted the magnitude of total mirid populations, and also shoot and pod damage in cocoa farms, albeit inconsistently.

Item Type: Thesis (PhD)
Additional Information: uk.bl.ethos.616530
Uncontrolled Keywords: insect pest control, cocoa crop,
Subjects: S Agriculture > SB Plant culture
Pre-2014 Departments: School of Science > Natural Resources Institute
Last Modified: 17 Mar 2017 11:02
Selected for GREAT 2016: None
Selected for GREAT 2017: None
Selected for GREAT 2018: None
URI: http://gala.gre.ac.uk/id/eprint/10335

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