Source and identity of insect contaminants in export consignments of table grapes

[摘要] The South African table grape industry exports approximately 60% of the tablegrapes produced. A major threat to the export of these grapes is the phytosanitary riskthat insect pests pose. This study was conducted in the Hex River Valley, SouthAfrica's main table grape producing area. The aim of this study was to reduce thenumber of phytosanitary rejections from insects on table grapes from the Hex RiverValley. Thus the main objectives of the study were to identify the most importantphytosanitary pests in the Hex River Valley; the determination of their presence in thevineyards with possible means to control them; and to assess the possibility of usingpostharvest quarantine treatments in the Western Cape. Further aims were todetermine the effect of different colour harvesting crates on the phytosanitary pests andwhether the phytosanitary pests infested the grapes via packhouses.The most important phytosanitary pests of table grapes of the Hex River Valleyare in order of importance: Phlyctinus callosus (Schonherr) (Coleoptera: Curculionidae),Epichoristodes acerbella Walker (Lepidoptera: Tortricidae), Planococcus ficus(Signoret) (Hemiptera: Pseudococcidae), Ceratitis capitata (Wiedemann) (Diptera:Tephritidae), Gonocephalum simplex Fabricius (Coleoptera: Tenebrionidae) andDysdercus fasciatus Signoret (Hemiptera: Pyrrhocoridae). 12.71% of rejections werefrom species that were not identified, while a further 33% of the rejections were possiblyidentified incorrectly.Phytosanitary control of P. callosus appeared to be far more effective usingPlantex® than pesticides. Weather conditions appeared to affect the abundance of P.callosus, especially warm weather, while bunches harboured less P. callosus later inthe day. Control of E. acerbella with DiPel® (Bacillus thuringiensis var. kurstaki)appeared to at least reduce the population within the vineyards, and so its use isrecommended. P. ficus is a non-actionable species for the USA market and is notlisted as a phytosanitary pest for the Israeli market and so should not be causing anyphytosanitary rejections. C. capitata appeared to be successfully controlled by the fruitfly sterile release program and the cold sterilisation it currently undergoes. G. simplexcaused few rejections. It is still unclear where this pest infests the grapes, as it was found in both the field and in the packhouses. D. fasciatus occurrence on grapes wasprobably accidental. It was shown that picking during the early and late parts of theday, when this species was less active, reduced its occurrence in bunches. Gryllusbimaculatus (De Geer) (Orthoptera: Gryllidae), although not reported as a reason forrejections in table grapes for the past two years, was an actionable species that waspresent in large numbers in the Hex River Valley. There was a strong correlationbetween increasing quantities of pesticides and higher abundances of G. bimaculatus.It appeared to be an indicator of the overuse of pesticides. Results of this studyshowed that infestation by the phytosanitary pests came from neighbouring vineyards.The creation of barriers to prevent the movement of these pests between vineyards issuggested.Methyl bromide is the most commonly used postharvest quarantine treatment.Owing to the ozone-depleting properties of methyl bromide, it is scheduled to beoutlawed in many countries from 2005. Alternative postharvest treatments areirradiation, extreme temperatures, forced air, vapour-heat treatments and the use ofcontrolled atmospheres. Irradiation treatments appeared to control the pests at dosesthat do not damage the grapes. Controlled atmosphere treatments also have a highprobability of success, although more research is required on this treatment. Lowtemperature treatments are relatively cheap as most exported fruit already undergoescold storage, and appears to control species in the families Pseudococcidae andTephritidae, although further research is required for the other pest.Colour or location of the harvesting crates in the vineyards appeared not toinfluence the number of phytosanitary pests collected, as they were not attracted tothese crates.

[发布机构] Stellenbosch University