Developing an integrated management system for westernflower thrips, Frankliniella occidentalis (Pergande), ondeciduous fruit, using semiochemicals in a push-pullstrategy

[摘要] ENGLISH ABSTRACT: Western flower thrips (WFT), Frankliniella occidentalis (Pergande), causes both feeding(russetting and silvering) and oviposition (pansy spot) damage to fruit. Despite routineinsecticide applications from 20% bloom until petal fall, pansy spot and pitting damage wasstill being reported, particularly on plums. This study was initiated to determine the reason forthe apparent failure of chemical control and the cause of pitting damage, and to investigatethe feasibility of developing a push-pull system to minimize economic WFT damage by usingdeterrent plant essential oils and trap crops.Field trials in commercial plum orchards in the Western Cape confirmed that WFT ovipositioncauses pitting damage. The apparent failure of insecticide applications to prevent pansy spotand pitting damage was due to the fact that WFT entered plum blossoms even before thepetals opened, where they were protected from contact insecticides applied at 20% bloom.No treatment threshold could be determined because no consistent significant relationshipwas found between blue sticky trap counts and WFT oviposition damage to plums. Sticky trapcounts thus only serve to indicate presence or absence of WFT in an orchard. To reduce WFToviposition damage, monitoring must start as soon as flower buds begin to swell, some bluesticky traps should be hung closer to the ground during the early season and, if WFT arepresent, 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 reduceWFT oviposition rate on plum blossoms was investigated. This study was the first todemonstrate that suspensions of thymol (10%), methyl salicylate (1% and 10%) and carvacrol(1% and 5%) significantly reduced WFT oviposition rate when applied to individual plumblossoms in laboratory bioassays. Significant results could not be obtained in semi-field trialsusing potted plum trees, mainly because the suspensions were unable to provide sustainedrelease of the volatile essential oils at behaviourally effective concentrations. Phytotoxicdamage to blossoms was encountered at higher concentrations of the essential oils. Whilethymol, methyl salicylate and carvacrol were shown to have potential as oviposition deterrentsfor WFT on plum blossoms, they could only be considered for commercial use if stablesuspensions can be developed to deliver sustained release of behaviourally effectiveconcentrations with no phytotoxic effects.An effective trap crop that provides the 'pull should be as attractive, or more attractive to WFTthan plum blossoms. White clover, Trifolium repens L., was selected for investigation. Theattractiveness 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 thevolatiles of clover flowers and plum blossoms are both very attractive to WFT females. Whiteclover shows potential as a trap crop for WFT, but a control system on heavily infested clovershould be implemented to remove WFT and clover flowers should be cut before honeybeesare brought in to ensure effective pollination.This study provided crucial information to improve the efficacy of early-season chemicalcontrol of WFT. Three essential oils were identified as potential oviposition deterrents for WFTon plum blossoms and white clover was identified as a potential trap crop. Development ofsuitable formulations of the essential oils is required before a push-pull system to manageWFT more sustainably in deciduous fruit orchards can be implemented.

[发布机构] Stellenbosch University