Developing an integrated management system for western flower thrips, Frankliniella occidentalis (Pergande), on deciduous fruit, using semiochemicals in a push-pull strategy

Allsopp, Elleunorah (2016-12)

Thesis (PhD)--Stellenbosch University, 2016.

Thesis

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.

AFRKAANSE OPSOMMING: Westelike blomblaaspootjie (WBB), Frankliniella occidentalis (Pergande), veroorsaak beide vreetskade (skilverruwing en versilwering) en eierleggingskade (“pansy spot”) by vrugte. Ten spyte van roetine insekdoder aanwendings vanaf 20% blom tot blomblaarval, is “pansy spot” en kuiltjieskade, veral by pruime, toenemend aangemeld. Hierdie studie is geloods om te bepaal waarom chemiese beheer nie skade tydens die blomstadium doeltreffend beheer nie, om die oorsaak van die kuiltjieskade te bepaal, en om die ontwikkeling van ‘n afweer-aanlok stelsel te ondersoek, wat ekonomiese WBB skade minimiseer deur gebruik van afwerende essensiële plantolies en vangoeste. Veldproewe in kommersiële pruimboorde in die Weskaap het bevestig dat eierlegging deur WBB kuiltjieskade veroosaak. Die skynbare onvermoë van insekdoders om “pansy spot” en kuiltjieskade te voorkom, was te wyte aan die feit dat WBB pruimbloeisels binnedring nog voordat die blomblare oopmaak, waar hulle beskerm was teen kontakmiddels wat op 20% blom toegedien is. Geen drumpelwaarde vir beheer kon bepaal word nie, aangesien daar geen konsekwent betekenisvolle verwantskap tussen blou lokvaltellings en WBB eierleggingskade by pruime was nie. Lokvaltellings dien dus slegs as ‘n aanduiding van die aan- of afwesigheid van WBB in ‘n boord. Om WBB eierleggingskade effektief te verminder, moet monitering begin sodra blomknoppe begin swel, taai lokvalle behoort aan die begin van die seisoen nader aan die grond gehang te word en, indien WBB teenwoordig, moet die eersre bespuiting aangewend te word sodra die bloeisels ballonstadium bereik. Om die afweringselement van ‘n afweer-aanlok stelsel te voorsien, is die potensiaal van drie essensiële plantolies om die eierleggingstempo van WBB op pruimbloeisels te verlaag, ondersoek. Hierdie studie was die eerste om te wys dat suspensies van timol (10%), metiel salisilaat (1% en 10%) en karvakrol (1% en 5%) WBB eierleggingstempo betekenisvol verlaag het in laboratoriumstudies met enkel pruimbloeisels. Betekenisvolle resultate kon nie verkry word in semi-veldroewe met pruimbome in potte nie, hoofsaaklik weens die onvermoë van die suspensies om volgehoue vrylating van vlugtige essensiële plantolies teen biologies effektiewe konsentrasies te voorsien. Hoër konsentrasies van die essensiële olies het fitotoksiese skade aan bloeisels veroorsaak. Alhoewel daar bewys is dat timol, metiel salisilaat en karvakrol potensiaal het om eierlegging deur WBB op pruimbloeisels te verhinder, kan hierdie verbindings slegs vir kommersiële gebruik oorweeg word indien stabiele suspensies ontwikkel kan word wat volgehoue, eweredige vrystelling biologies effektiewe konsentrasies sonder enige fitotoksiese effek verseker. ‘n Doeltreffende vangoes wat die aanlokkingselement van ‘n afweer-aanlok stelsel voorsien, behoort ewe of meer aanloklik vir WBB te wees as pruimbloeisels. Wit klawer, Trifolium repens L., is gekies vir die ondersoek na ‘n potensiële vangoes. Die vlugtige verbindings van klawerblomme en pruimbloeisels is versamel en die aanloklikheid daarvan is met behulp van ‘n Y-buis olfaktometer bepaal. Resultate het gewys dat die vlugtige verbindings van klawerblomme en pruimbloeisels beide hoogs aanloklik is vir WBB. Wit klawer het potensiaal as ‘n vangoes vir WBB, maar om doeltreffende bestuiwing te verseker, sal WBB op die klawer vroegtydig beheer en die klawerblomme afgesny moet word voordat bye in die boorde ingebring word. Hierdie studie het uiters noodsaaklike inligting verskaf om die doeltreffendheid van chemiese beheer van blaaspootjies vroeg in die seisoen te verbeter. Drie essensiële olies is as potensiële afweermiddels vir eierlegging deur WBB op pruimbloeisels geïdentifiseer en wit klawer is geïdentifiseer as ‘n potensiële vangoes. Ontwikkeling van geskikte formulasies van die essensiële plantolies is ‘n voorvereiste vir implementering van ‘n afweer-aanlok stelsel om WBB meer volhoubaar te bestuur.

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