Browsing by Author "Hoffmann, John"

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    Biological control of Acacia cyclops in South Africa : the role of an introduced seed-feeding weevil, Melanterius servulus (Coleoptera: Curculionidae), together with indigenous seed-sucking bugs and birds
    (2005) Impson, F A C; Hoffmann, John; Moran, Cliff
    Acacia cyclops A. Cunn ex G. Don, or rooikrans (Fabaceae), of Australian origin, is an invasive environmental weed in South Africa where it threatens the unique vegetation of the Cape Floral Kingdom. The invasiveness of the plant in South Africa is, in part, due to its high annual seed-yields, together with the suitable climatic and edaphic factors found here. This study investigated the role of a seed-feeding weevil, Melanterius servulus, which was first introduced into South Africa during 1991, as a biological control agent of A. cyclops seeds, together with the combined effects of indigenous seed-sucking bugs and birds. The weevils utilise filled green pods of A. cyclops for adult feeding, oviposition and larval development and completely destroy seeds during these activities. Examination of the reproductive phenology of A. cyclops showed that seeds are produced annually, during summer and that the presence of filled green pods on the plants coincides with the period of reproductive activity of the weevils. Melanterius servulus populations have established readily at all the original release sites, and within four years of release, damage levels to seeds commonly reached 90%. The weevils have dispersed at an average rate of approximately 2 km per year. Since becoming established in South Africa. the seeds of A. cyclops have been utilised by a variety of generalist vertebrate and invertebrate organisms. Indigenous polyphagous alydid bugs feed on the mature seeds, rendering a portion of the crop inviable when damage levels are high (more than five feeding-punctures per seed). Several bird species are attracted to and feed on the fleshy aril that surrounds theseeds of A. cyclops. Passage of the seeds through the gut of birds enhances germination rates. There is a synergetic relationship between alydids and birds because seeds with low levels of alydid feeding (one to four punctures per seed) germinated more readily after passage through birds than seeds that were not eaten by birds.
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    Biological control of alien species (Prosopis) in South Africa : the role of introduced seed-feeding bruchids
    (2006) Roberts, Anthony Paul; Hoffmann, John
    The use of bruchid beetles for biologicval control of mesquite, Prosopsis species, in South Africa is deemed to have failed because the beetles are supposed to be unable to compete with livestock which utilise the seed pods of mesquite extensively as forage. These assumptions have been made without any evidence as to how the beetles and livestock interact or as to whether mesquite is site or seed limited in South Africa. This study was initiated to test the hypothesis that the beetles are not coping with competition with livestock and that mesquite is site limited and not seed limited in South Africa.
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    A biophysical and economic evaluation of biological and chemical control methods for Solanum elaegnifolium (Silverleaf Nightshade) in the Limpopo province, South Africa
    (2010) Pitso, Dikeledi Confidence; Hoffmann, John; Wise, Russell
    The results showed that the difference in the weed density was insignificant, indicating that biological and chemical control were both effective in the management of S. elaeagnifolium. However biological control was shown to be more economically beneficial than chemical control, since there was a net gain as a result of lower costs using L. texana beetles. Further research is needed to determine the effectiveness of L. texana and damage caused by S. elaeagnifolium on expected yield to conduct a full cost-benefit analysis.
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    Climatic change, habitat modification and relative age of dung beetle taxa (Coleoptera: Scarabaeidae, Hydrophilidae, Histeridae, Staphylinidae) in the South-Western Cape
    (1990) Davis, Adrian Louis Victor; Moran, Cliff; Hoffmann, John
    1. Two study sites near Pretoria in the Transvaal were located in a summer rainfall climatic area, type 113d (Walter & Lieth 1964), on deep and in both open woodland and grassland. 2. Eleven study sites in the south-western Cape were distributed between two winter rainfall climatic areas, type IV in the Cape of Good Hope Peninsula and type III(IV)a (Walter & Lieth 1964) on the west coast. The west coast could be divided into two subregions, the coastal belt of deep calcareous sand and the Darling Hills comprising predominantly sandy soils with a higher clay fraction. Vegetation at the sites formed a gradient from low, dense pasture to taller sparser shrubland; The five pasture sites were distributed between all three subregions whereas the six shrubland sites were located only in the Cape of Good Hope Peninsula and on the west coastal belt. 3. Pitfall traps baited with cattle dung were used to sample dung beetle fauna over 24h periods once a week in the Transvaal, irrespective .of weather (three traps/site), and on three sunny occasions per month in the south-western Cape (ten traps/site) for one year. 4. A further 13 study sites used for back-up studies in the south-western Cape were concentrated into three localities, three in the Cape of Good Hope Peninsula, six on the west coastal plain and four-in the Darling Hills. These sites comprised different combinations of pasture (five sites) and shrubland (eight sites) habitats. Five traps at each site were baited on one 24h occasion each month over six months.
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    Friend or foe? The arrival of Stator limbatus (Bruchidae) in South Africa
    (2013) Rink, Ariella; Hoffmann, John
    Stator limbatus is a generalist seed-feeding beetle (Coleoptera: Bruchidae) whose natural range extends from the southern USA to Latin America. Individuals have recently been collected in the Western Cape province of South Africa in seeds of the invasive alien plant species Acacia mearnsii and A. cyclops. This study conducted a preliminary examination of its oviposition preference, and development on, a number of indigenous and invasive alien Acacia species and the invasive alien Paraserianthes lophantha (all Fabaceae). Oviposition preference appears to be for larger seeds but A. ataxacantha was found to be the only indigenous host suitable for larval development.
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    Neltumius arizonensis (Schaeffer) (Coleoptera: Bruchidae) as a biological control agent of mesquite (Prosopis spp., Mimosaceae) in South Africa
    (1996) Coetzer, Willem; Hoffmann, John; Moran, Cliff
    In the late nineteenth century, six North American mesquite taxa (Prosopis spp., Mimosaceae) were introduced into South Africa. They were to provide shade for livestock, and their pods were valued as a source of fodder. All Prosopis species in south Africa were recognized, as weeds in 1983. In 1987 a biological control programme using seed weevils (Coleoptera: Bruchidae) was launched against the two most invasive taxa, namely, P. glandulosa var. torreyana (L. Benson) M.C. Johnston and P. velutina Wooton. Algarobius prosopis (Leconte), the first biocontrol agent released, destroys large numbers of mesquite seeds annually, where livestock do not graze pods that are lying on the ground. Where pods are grazed, however, there is insufficient time for A. prosopis to inflict an adequate degree of seed damag'e before pods are eaten. For this reason another bruchid, Neltumius arizonensis (Schaeffer), which was reported to be capable of ovipositing on immature and mature tree-borne pods, was released in 1993. The establishment of N. arizonensis on mesquite at three sites in Western Cape Province was confirmed by monitoring N. arizonensis oviposition and emergence in the field. High levels of oviposition by N. arizonensis on tree-borne pods in June 1994 (39 and 29 'egg-seeds' at Onderplaas and Clanwilliam, respectively) were accompanied by high rates of trichogrammatid egg parasitism. Most pods had fallen to the ground by this time. The degree of egg parasitism was independent of N. arizonensis egg density. From December 1994 until June 1995, N. arizonensis egg densities were lower than those recorded in June 1994. The rate of field oviposition by N. arizonensis returned to high levels in August and September 1995, when 'tree pods' were again few in number. Neltumius arizonensis eggs were more abundant on 'tree pods' than on 'ground pods' in August and September 1995.
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    Prediction of safety and effectiveness of a candidate biocontrol agent : quarantine evaluation of the root-feeding, Mexican flea beetle, Longitarsus bethae, for potential release against the noxious weed, Lantana camara, in Africa
    (2006) Simelane, David Okhi; Hoffmann, John; Urban, A J
    A root-feeding, Mexican flea beetle, Longitarsus bethae Savini & Escalona 2005 (Coleoptera: Chrysomelidae: Alticinae), was evaluated in quarantine as a candidate biological control agent for the noxious weed, Lantana camara L. (Verbenaceae). The premise was that L. bethae would only be released if it could be ascertained that it was: (i) safe for non-target plants; (ii) likely to inflict significant damage on the target weed; and (ii) capable of surviving under the various (abiotic and biotic) environmental conditions in its new range.
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    Seed-reducing Cecidomyiidae as potential biological control agents for invasive Australian wattles in South Africa, particularly Acacia mearnsii and A. cyclops
    (2004) Adair, Robin John; Hoffmann, John
    The collection of gall-forming Cecidomyiidae specimens and their parasitoids from Australia and South Africa during this project produced a large and valuable assemblage of material, most of which will be or has been lodged with the National Insect Collection (Pretoria) (parasitoids) or the South Australian Museum Adelaide (cecidomyiids).
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    Wasps (Hymenoptera: Chalcidoidea) associated with galls in seed-capsules of Eucalyptus camaldulensis (Myrtaceae) in South Africa : species composition, trophic relationships and effects
    (2009) Klein, Hildegard; Hoffmann, John
    The Australian river red gum (Eucalyptus camaldulensis Denhardt) (Myrtaceae) is regarded in South Africa as a valuable general-purpose utility and ornamental tree, as well as an essential source of nectar and pollen to sustain the honeybees which are crucial for pollinating the economically important fruit crops in mainly the Western Cape Province. Despite its utility value, it is regarded as invasive in South Africa, the major concern being the large amounts of water it consumes when growing along watercourses. River red gum is therefore the subject of conflicts in interests between government agencies that target it for control actions, and farmers and beekeepers who utilize it. As a contribution towards resolving this conflict in interests, a research project was initiated to investigate the potential use of host-specific insects that might reduce the number of viable seeds produced by E camaldulensis. The aim was to reduce its invasive potential while retaining its general utilizability for all concerned. From the start, the need for introduced agents from Australia was weighed against the presence of two species of chalcidoid wasps, both regarded as gall inducers, in the seed capsules of E camaldulensis in South Africa. The current study was motivated by the need for information on the biology of these two species and the effect they were having on seed production in their host plant. As it progressed, three more chalcidoid species, all undescribed at that time and probably of Australian origin, were found to be emerging from the seed capsules of E camaldulensis collected in several parts of South Africa, and these became part of the investigation.
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    Wasps (Hymenoptera: Chalcidoidea) associated with galls in seed-capsules of Eucalyptus camaldulensis (Myrtaceae) in South Africa : species composition, trophic relationships and effects
    (2009) Klein, Hildegard; Hoffmann, John
    The Australian river red gum (Eucalyptus camaldulensis Denhardt) (Myrtaceae) is regarded in South Africa as a valuable general-purpose utility and ornamental tree, as well as an essential source of nectar and pollen to sustain the honeybees which are crucial for pollinating the economically important fruit crops in mainly the Western cape Province. Despite its utility value, it is regarded as invasive in South Africa, the major concern being the large amounts of water it consumes when growing along watercourses. River red gum is therefore the subject of conflicts in interests between government agencies that target it for control actions, and farmers and beekeepers who utilize it. As a contribution towards resolving this conflict in interests, a research project was initiated to investigate the potential use of host-specific insects that might reduce the number of viable seeds produced by E. camaldulensis. The aim was to reduce its invasive potential while retaining its general utilizability for all concerned. From the start, the need for introduced agents from Australia was weighed against the presence of two species of chalcidoid wasps, both regarded as gall inducers, in the seed capsules of E. camaldulensis in South Africa. The current study was motivated by the need for information on the biology of these two species and the effect they were having on seed production in their host plant. As it progressed, three more chalcidoid species, all undescribed at that time and probably of Australian origin, were found to be emerging from the seed capsules of E. camaldulensis collected in several parts of South Africa, and these became part of the investigation. The aims of this study were to determine • which species was the gall inducer(s), • the role of each of the other associated hymenopteran species in the gall, • the extent to which these hymenopteran species affected the reproductive potential of E. camaldulensis, and ultimately, • whether this complex of hymenopteran species, or any single speCies, had the potential to reduce the invasive potential of E. camaldulensis in South Africa, and therefore to serve as biocontrol agents in an integrated management plan of Eucalyptusspp. in South Africa. The first chapter is a literature study, which deals with the possible biological role of each of the five chalcidoid species associated with the galls in the seed capsules of trees in the Eucalyptus camaldulensiscomplex. They are: Megastigmus zebrinusGrisseli (Torymidae: m Megastigminae); Quadrastichode/la nova Girault (Eulophidae: Tetrastichinae); Leprosa milga Kim & La Salle (Eulophidae: Tetrastichinae); Aprostocetus sp. (Eulophidae: Tetrastichinae); and another undescribed species (Eulophidae: Tetrastichinae, genus indet.)/ which will be referred to as Eulophid #4 and is characterised by a distinct elongate hypopygium. An account is also given of galls, their development and biology, and of gall inducers and other associated insects, e.g. parasitoids, predators and inquilines. Chapter 2 deals with the geographical distribution of the seed capsule galls of E. camaldulensis in South Africa, and with the hymenopteran species that were reared from the samples collected from various parts of the country and during different periods of the year. It also discusses the emergence patterns of the various hymenopteran gall inhabitants, as observed during a detailed, one-year survey of three test trees in different parts of Pretoria. The emergence patterns of the insects are correlated with the phenology of the test trees, as recorded during the same period. Chapter 3 describes attempts to determine the biological role of each of the five chalcidoid gall inhabitants. This entails the dissection of flowerbuds, flowers and seed capsules of E. camaldulensis, oviposition trials in sleeves on intact trees, and the laboratory observation of adults. In some of the cases it was possible to identify the juveniles that were encountered during dissections by matching DNA sequences of the juveniles and of adults. By following all the available leads, it was concluded that Q. nova is the primary gall inducer, that L. milga probably parasitizes Q. nova, and that M. zebrinus is a parasitoid of either Q. nova or L. milga, but that its larvae also feed on gall tissue. Aprostocetus is possibly a parasitoid of L. milga. The last species (Eulophid #4) was not abundant enough to allow studies of its biology. In the final chapter, an account is given of the effect of galling on seed production in the three E. camaldulensistrees in Pretoria, as an indication of the ability of the gall inducer to reduce the invasiveness of E. camaldulensis in South Africa without compromising its valuable attributes. It was concluded that the presence of galls in the seed capsules significantly reduced the number of viable seeds in the capsule. This seed reduction could be expected to reduce the spread of E. camaldulensis where it grows along watercourses, which is also where it is most invasive. This study has expanded the available knowledge on the trophic relationships of chalcidoid wasps associated with eucalypts by showing that: • the tetrastichine Quadrastichodella nova induces galls in the seed capsules of trees of the Eucalyptus camaldulensiscomplex in South Africa; • the galls develop in the placenta of one of the locules in the seed capsule, and are not modified seeds, or outgrowths from the capsule wall, as previously believed; • galling of the seed capsules reduces the production of viable seeds in £ camaldulensis, • at least three parasitic chalcidoid species are associated with these galls; • of these, the tetrastichine Leprosa milga probably parasitizes the larvae of the gall inducer; • the tetrastichine Aprostocetus is possibly a hyperparasitoid of L milga; • the torymid Megastigmus zebrinus is a parasitoid that also feeds on gall tissue; • several authors referring to M. zebrinus and L milga as gall inducers have been mistaken.