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

[摘要] 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 solelyrely on chemical pesticides. Past studies in South Africa have shown that Proteaceaecomprise a rich and diverse arthropod fauna. However, as most of these studies wereconducted 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. thefeeding guilds found in proteas. The aim of this research was to conduct an intensive andextensive survey of the arthropod-fauna associated with commercially-cultivated proteasacross an entire year. Specifically, this survey was designed to document the composition ofthe arthropod fauna (creating a comprehensive reference collection for pest managementpurposes) and to assess whether the arthropod fauna differed between seasons and pesticidetreatments.Infructescences, inflorescences and foliage of mainly commercial Proteaceae were sampledfor arthropods seasonally for a period of twelve months by collection of plant material anddirect searching. Seven commercial protea blocks, and a wild protea block (remnant patch offynbos vegetation), were used as the sampling sites, and two sprayed blocks were used forassessing pesticide efficacy. Individual arthropods were identified as far as possible, with37% 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 werecollected 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 themost abundant (72%) and speciose (25%). In addition to phytophages, there was a large suiteof insect predators and parasitoids. A large number of the arthropods were endemic to theCape Floristic Region (CFR) and some (7.86%) have a pest status, in that they causesignificant damage to the protea plants (for example, 60% of Safari sunset cultivar(Leucadendron salignum x L. laureolum) new flush stems and leaves were affected byEpichoristodes acerbella (Tortricidae). Capys alphaeus (Lycaenidae) and Phyllocnistis sp.(Phyllocnistidae) appear to be specialist pests, as they attack mainly Protea cynaroides andSusara cultivar (Protea magnifica x P. susannae) respectively.Arthropod abundance did not differ significantly between seasons, although significantseasonal effects were observed in species richness when the protea cultivars were examinedseparately. Pesticide application did not affect arthropod abundance, but did decrease speciesrichness in sprayed blocks. Pesticides appeared to negatively affect minor (rare) speciesdisproportionately, probably due to their lack of prior exposure to pesticides and hencesensitivity. Due to this inefficacy of pesticides in cultivated proteas, an increasing emphasison the importance of non-chemical control measures, and our improved knowledge of thepredatory and parasitic species in this system, integrated pest management strategies deservegreater research attention.Monitoring and use of threshold values for arthropod pests were suggested here, as well asthe use of biological, cultural, physical and chemical (optimal use) control. For instance, incultural control, polycropping and intercropping in proteas to increase plant diversity in themonocultures to promote a higher density of predators and parasitoids can be used. Certainflowering plants are known to provide greater temporal and spatial distribution of nectar andpollen sources, which can increase parasitoid reproductive potential and abundance ofalternative hosts/prey when the pest species are scarce or at an inappropriate stage.

[发布机构] Stellenbosch University