Habitat preferences of the invasive harlequin ladybeetle Harmonia axyridis (Coleoptera: Coccinellidae) in the Western Cape Province, South Africa
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The invasive and predatory harlequin lady beetle, Harmonia axyridis, has been introduced as a biological control agent to many agricultural areas worldwide and has now spread from agricultural to natural habitats where it threatens native arthropod biodiversity. The aim of this study was to determine how H. axyridis uses the local landscape during different times of the year in the Western Cape Province, South Africa. We also determined its association to native arthropod diversity. Harmonia axyridis adults and larvae, as well as arthropod herbivores, predators and other ladybeetles were sampled every second month for a year with a vacuum sampler in vineyards, natural habitats, edges between natural habitats and vineyards, and urban areas. Highest adult and larval H. axyridis abundance occurred in urban areas during all sampling periods, with a peak in May and July (winter). Vineyards and natural vegetation had very low abundances of H. axyridis. Harmonia axyridis had some, but limited effect on the local arthropod community abundance. There was also a negative relationship between H. axyridis and the overall arthropod community as well as a positive relationship between H. axyridis abundance and that of other ladybeetles. Harmonia axyridis appeared to influence the assemblage composition of other ladybeetles and herbivores. Overall, the native arthropod assemblage responded primarily to season and habitat and secondary to the presence of H. axyridis. Harmonia axyridis has a strong association with the urban environment, seemingly in association with the exotic aphid Tuberculatus annulatus that feeds on cultivated oak trees. Outside of the urban area, H. axyridis numbers were very low and its ecological impacts may be negligible.