Department of Conservation Ecology and Entomology

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Browsing Department of Conservation Ecology and Entomology by Author "Allsopp, Elleunorah"

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    Developing an integrated management system for western flower thrips, Frankliniella occidentalis (Pergande), on deciduous fruit, using semiochemicals in a push-pull strategy
    (Stellenbosch : Stellenbosch University, 2016-12) Allsopp, Elleunorah; Addison, Pia; Dewhirst, Sarah Y.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: Western flower thrips (WFT), Frankliniella occidentalis (Pergande), causes both feeding (russetting and silvering) and oviposition (pansy spot) damage to fruit. Despite routine insecticide applications from 20% bloom until petal fall, pansy spot and pitting damage was still being reported, particularly on plums. This study was initiated to determine the reason for the apparent failure of chemical control and the cause of pitting damage, and to investigate the feasibility of developing a push-pull system to minimize economic WFT damage by using deterrent plant essential oils and trap crops. Field trials in commercial plum orchards in the Western Cape confirmed that WFT oviposition causes pitting damage. The apparent failure of insecticide applications to prevent pansy spot and pitting damage was due to the fact that WFT entered plum blossoms even before the petals opened, where they were protected from contact insecticides applied at 20% bloom. No treatment threshold could be determined because no consistent significant relationship was found between blue sticky trap counts and WFT oviposition damage to plums. Sticky trap counts thus only serve to indicate presence or absence of WFT in an orchard. To reduce WFT oviposition damage, monitoring must start as soon as flower buds begin to swell, some blue sticky traps should be hung closer to the ground during the early season and, if WFT are present, the first spray application should be made as soon as blossoms reach balloon stage. To provide the “push” in a push-pull system, the potential of three plant essential oils to reduce WFT oviposition rate on plum blossoms was investigated. This study was the first to demonstrate that suspensions of thymol (10%), methyl salicylate (1% and 10%) and carvacrol (1% and 5%) significantly reduced WFT oviposition rate when applied to individual plum blossoms in laboratory bioassays. Significant results could not be obtained in semi-field trials using potted plum trees, mainly because the suspensions were unable to provide sustained release of the volatile essential oils at behaviourally effective concentrations. Phytotoxic damage to blossoms was encountered at higher concentrations of the essential oils. While thymol, methyl salicylate and carvacrol were shown to have potential as oviposition deterrents for WFT on plum blossoms, they could only be considered for commercial use if stable suspensions can be developed to deliver sustained release of behaviourally effective concentrations with no phytotoxic effects. An effective trap crop that provides the “pull” should be as attractive, or more attractive to WFT than plum blossoms. White clover, Trifolium repens L., was selected for investigation. The attractiveness of flower volatiles of clover flowers and plum blossoms, collected by means of air entrainment, was evaluated using a Y-tube glass olfactometer. Results showed that the volatiles of clover flowers and plum blossoms are both very attractive to WFT females. White clover shows potential as a trap crop for WFT, but a control system on heavily infested clover should be implemented to remove WFT and clover flowers should be cut before honeybees are brought in to ensure effective pollination. This study provided crucial information to improve the efficacy of early-season chemical control of WFT. Three essential oils were identified as potential oviposition deterrents for WFT on plum blossoms and white clover was identified as a potential trap crop. Development of suitable formulations of the essential oils is required before a push-pull system to manage WFT more sustainably in deciduous fruit orchards can be implemented.