Arthropods associated with commercial Proteaceae in the Western Cape Province, South Africa

Sasa, Archbold (2011-03)

Thesis (MSc)--University of Stellenbosch, 2011.

Thesis

ENGLISH ABSTRACT: The commercial cultivation of Proteaceae is an important industry in the Western Cape, however, farmers are challenged with arthropod infestation which compels them to solely rely on chemical pesticides. Past studies in South Africa have shown that Proteaceae comprise a rich and diverse arthropod fauna. However, as most of these studies were conducted on wild Proteaceae, they may not be representative of cultivated proteas. Moreover, most of these species remained unidentified due to lack of identification expertise. These past studies, however, form a useful baseline for arthropod studies in proteas, e.g. the feeding guilds found in proteas. The aim of this research was to conduct an intensive and extensive survey of the arthropod-fauna associated with commercially-cultivated proteas across an entire year. Specifically, this survey was designed to document the composition of the arthropod fauna (creating a comprehensive reference collection for pest management purposes) and to assess whether the arthropod fauna differed between seasons and pesticide treatments. Infructescences, inflorescences and foliage of mainly commercial Proteaceae were sampled for arthropods seasonally for a period of twelve months by collection of plant material and direct searching. Seven commercial protea blocks, and a wild protea block (remnant patch of fynbos vegetation), were used as the sampling sites, and two sprayed blocks were used for assessing pesticide efficacy. Individual arthropods were identified as far as possible, with 37% identified to species level. A species accumulation curve showed that rare (minor) arthropod species made up of 70% of arthropods occurring in cultivated proteas. More than 8 700 individuals from more than 140 species and about 80 families were collected and identified, revealing that cultivated proteas have a rich and diverse insect fauna. These arthropods represent the full range of plant-feeding guilds: leaf miners, leaf chewers, flower bud borers, sap suckers and seed feeders. Flower visitors/free living guild was the most abundant (72%) and speciose (25%). In addition to phytophages, there was a large suite of insect predators and parasitoids. A large number of the arthropods were endemic to the Cape Floristic Region (CFR) and some (7.86%) have a pest status, in that they cause significant damage to the protea plants (for example, 60% of Safari sunset cultivar (Leucadendron salignum x L. laureolum) new flush stems and leaves were affected by Epichoristodes acerbella (Tortricidae). Capys alphaeus (Lycaenidae) and Phyllocnistis sp. (Phyllocnistidae) appear to be specialist pests, as they attack mainly Protea cynaroides and Susara cultivar (Protea magnifica x P. susannae) respectively. Arthropod abundance did not differ significantly between seasons, although significant seasonal effects were observed in species richness when the protea cultivars were examined separately. Pesticide application did not affect arthropod abundance, but did decrease species richness in sprayed blocks. Pesticides appeared to negatively affect minor (rare) species disproportionately, probably due to their lack of prior exposure to pesticides and hence sensitivity. Due to this inefficacy of pesticides in cultivated proteas, an increasing emphasis on the importance of non-chemical control measures, and our improved knowledge of the predatory and parasitic species in this system, integrated pest management strategies deserve greater research attention. Monitoring and use of threshold values for arthropod pests were suggested here, as well as the use of biological, cultural, physical and chemical (optimal use) control. For instance, in cultural control, polycropping and intercropping in proteas to increase plant diversity in the monocultures to promote a higher density of predators and parasitoids can be used. Certain flowering plants are known to provide greater temporal and spatial distribution of nectar and pollen sources, which can increase parasitoid reproductive potential and abundance of alternative hosts/prey when the pest species are scarce or at an inappropriate stage.

AFRIKAANSE OPSOMMING: Die kommersiële verbouing van Proteaceae (proteas) is 'n belangrike bedryf in die Wes-Kaap. Menige plantasie wemel egter van artropodes, wat boere noop om slegs van chemiese plaagdoders gebruik te maak. Vorige studies in Suid-Afrika toon dat proteas die gasheerplant vir 'n ryke en diverse artropodefauna is. Aangesien die meeste van hierdie studies egter op wilde proteas uitgevoer is, weerspieël dit moontlik nie die stand van sake met verboude proteas nie. Weens 'n gebrek aan kundigheid om die artropodes te eien word baie van die spesies boonop nooit uitgeken nie. Dié studies voorsien egter 'n nuttige grondlyn vir 'n ondersoek na die artropodes op proteas, veral vir die bestudering van die gilde wat van die protea leef (“the feeding guild”). Hierdie navorsing het ten doel om 'n intensiewe en omvattende opname te maak van die artropodefauna wat oor die tydperk van 'n jaar op kommersieel verboude proteas voorkom. Die opname is meer bepaald ontwerp om die samestelling van die artropodefauna te bestudeer (deur 'n omvattende verwysingsversameling vir plaagbestuurdoeleindes te skep), en om vas te stel of seisoene en plaagbehandelings enige beduidende uitwerking op die artropodefauna het. Oor 'n tydperk van 12 maande is seisoenale monsters van die vrug- en bloeistadia, saadkoppe en blare van hoofsaaklik kommersiële proteas gesoek en ingesamel. Sewe kommersiële proteablokke sowel as 'n blok wilde proteas het as proefpersele gedien, en twee bespuite blokke is gebruik om die doeltreffendheid van plaagdoder te beoordeel. Individuele artropodes is so noukeurig moontlik uitgeken – 37% tot op spesievlak. Volgens 'n spesieakkumulasiekurwe maak seldsame (kleiner) artropodespesies sowat 70% van die artropodes uit wat op verboude proteas voorkom. Die meer as 8 700 individue van meer as 140 spesies en sowat 80 families wat ingesamel en uitgeken is, toon die rykheid en diversiteit van die artropodefauna op verboude proteas. Hierdie artropodes verteenwoordig die volle reeks plantvreterspesies – van blaardelwers en blaarkouers tot blomknopboorders, sapsuiers en saadvreters. Blombesoeker-/vrylewende spesies was die volopste (72%) en mees divers (25%). Buiten plantvreters was daar ook 'n groot aantal roofinsekte en parasitoïede. Baie van die artropodes was inheems, en sommige (7,86%) het boonop plaagstatus, aangesien hulle beduidende skade aan die proteaplant aanrig. [By ongeveer 60% van die Safari Sunset-kultivar (Leucadendron salignum x L. laureolum) is nuwe stamme en blare byvoorbeeld deur die Epichoristodes acerbella (Tortricidae) aangetas.] Capys alphaeus (Lycaenidae) en Phyllocnistis sp. (Phyllocnistidae) blyk spesialisplae te wees wat onderskeidelik hoofsaaklik die Protea cynaroides en die Susarakultivar (Protea magnifica x P. susannae) in die visier het. Artropodegetalle het nie juis tussen seisoene gewissel nie, hoewel 'n afsonderlike ondersoek van die proteakultivars 'n beduidende seisoenale uitwerking op spesierykheid aan die lig gebring het. Eweneens het die toediening van plaagdoder nie die artropodegetalle verminder nie, maar wel spesierykheid op die bespuite blokke verswak. Plaagdoders blyk besonder negatiewe uitwerking op kleiner (seldsame) spesies te hê – waarskynlik omdat dié spesies nie voorheen aan plaagdoders blootgestel was nie, en dus gevoelig is daarvoor. Weens die oënskynlike ondoeltreffendheid van plaagdoders op verboude proteas, verg 'n toenemende klem op die belang van niechemiese beheermaatreëls, 'n behoefte aan meer kennis van die roof- en parasitiese spesies in die stelsel, en die vraag na geïntegreerde plaagbeheerstrategieë, meer navorsing. Die studie moniteer en gebruik drempelwaardes vir artropodeplae, sowel as biologiese, kulturele, fisiese én chemiese (‘optimalegebruik’-) plaagbeheer. Met kulturele beheer kan poli- en interverbouing van proteas byvoorbeeld gebruik word om plantdiversiteit in die monokulture te verbeter, ten einde só 'n hoër digtheid van roofspesies en parasitoïede in die hand te werk. Sekere blomplante bied kenmerkend 'n wyer tyd- en ruimtelike verspreiding van nektar- en stuifmeelbronne, wat parasitoïede se voortplantingsvermoë en die getalle van alternatiewe gashere/prooi kan verbeter wanneer die plaagspesies skaars is of in 'n ontoepaslike stadium verkeer.

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