Browsing by Author "Hoffmann, John Hugh"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Open Access
    Taxonomy and Life History of Gall Midges (Diptera, Cecidomyiidae) on Drosanthemum and Malephora (Aizoaceae) in South Africa
    (2021) Van Munster, Stephany; Dorchin, Netta; Colville, Jonathan; Hoffmann, John Hugh
    South Africa is known for its highly endemic and remarkably species-rich fauna and flora. The Greater Cape Floristic Region, consisting of the Cape Floristic Region and the Succulent Karoo Region, is home to South Africa's second most diverse plant family, the Aizoaceae. While the Aizoaceae are relatively well studied, there has been little work done on their associated insect fauna. Preliminary observations in recent years revealed a diverse community of gall midges on these plants. This study aimed to investigate the gall midges associated with two speciose genera of Aizoaceae and it is the first of its kind in South Africa. I report five new species of gall midges, three belonging to Asphondylia Loew and two to Lasioptera Meigen. These species are described from several species within the Aizoaceae genera Drosanthemum Schwantes and Malephora N.E.Br., and additional host records were recorded from Lampranthus N.E.Br., Carpobrotus N.E.br., Acrodon N.E.Br., Cephalophyllum Haw. and Jordaaniella H.E.K. Hartmann. The gall midges are described from adults, pupae and larvae and information is provided on their galls, life history and distribution. Morphological attributes of the gall midges support the description of five distinct species. Furthermore, morphological characters of the Lasioptera species described here do not fit entirely with those of the genus, suggesting that a new genus should be established for them. These results provide a mere snapshot of the gall midge diversity that is to be found on Aizoaceae in southern Africa, and much work is still to be done on the Cecidomyiidae of South Africa as a whole. Further targeted sampling may reveal greater distribution ranges and additional host plants for the five species described here, as well as many more undescribed species across the Aizoaceae.
  • Thumbnail Image
    Item
    Open Access
    The role of certain mortality factors in the underperformance of Aristaea (Parectopa) thalassias (Meyrick) as a biological control agent of Leptospermum laevigatum F. Muel.
    (2021) Mlokoti, Thembelihle; Hoffmann, John Hugh; Lyons, C; Impson, F
    Leptospermum laevigatum is indigenous to the coasts of south and central New South Wales in Australia. It has become invasive in South Africa since its introduction in the 1800s, competing with the native fynbos across the coastal regions of the Western Province and into the Eastern Cape Province. Due to its aggressive spread, it became a significant concern and is considered a highly invasive species requiring a concerted management plan in South Africa. Biological control of L. laevigatum has been implemented since the 1980s with limited success to date. Aristaea (Parectopa) thalassias is one of two biological control agents introduced against L. laevigatum and is present across the plant's distribution along the coastal regions of the Western Cape Province and into the Eastern Cape Province in South Africa. In order to understand the limited success of A. thalassias, this study considers the biology of the immature stages, larval mortality due to parasitoids, predation and overcrowding, and seasonal influences on development and survival. The findings showed that A. thalassias is present throughout the year, completes its life cycle in 58 days (as measured in spring), and thus has the potential to complete several overlapping generations throughout the year. Levels of overall mortality of larvae, pre-pupae and pupae averaged over a 20-month period indicated seasonal variability, with highest mortality in autumn and winter. Mortality attributed to parasitism was highest in summer (maximum 25% in one year). Furthermore, predation and overcrowding (maximum 15%) were also low, and thus these mortality factors are unlikely to account for the low efficacy of the agent. Despite this, mortality through other unknown factors was at times found to be high, especially for first instar larvae in mined leaves (maximum 58% in one year). The peak oviposition period was not aligned with the peak in production of new leaves, suggesting a possible phenological mismatch between L. laevigatum and its biological control agent A. thalassias which could curb population expansion. Whilst mortality resulting from unknown factors (i.e., not investigated in the scope of this study) might be playing an important role in the performance of A. thalassias, specific factors investigated during this study could not explain why the moth is not more prolific. Determining why any particular biological control agent is ineffective is often not a straightforward exercise because it may be the result of a complex of interacting factors, which are not easily discernible. The findings of this study show that this is probably true for A. thalassias in South Africa and much more work is needed to resolve the reasons for its underperformance as a biological control agent.