M.Sc. (Zoology) / This study centres around the findings on mites (Acari: Eriophyidae) (also referred to as "eriophyids") as potential biological control agents of weeds in South Africa. The use of mites in the biological control of weeds is briefly reviewed. Four species of the family Eriophyidae have been used against weeds in other countries. Seventeen eriophyid species, causing symptoms possibly of significance to biological weed control of 12 plant species regarded as weeds in South Africa, are discussed. Methods to rear and study eriophyids in the laboratory have not yet been fully developed and studying these practically invisible arthropods, very closely associated with their host plants, frequently presents difficulties. Reported methods, and those used for the present study, are reviewed and discussed. The eriophyid, Aceria lantanae (Cook), causing flower and leaf galls on Lantana camara L. could not be successfully established in a quarantine laboratory on potted plants propagated from cuttings of L. camara forms from South Africa. The results obtained during this attempt were inconclusive. The failure of establishment on local L. camara forms could be attributed to a variety of factors, of which rearing methods and host incompatibility are the most likely. Convolvulus arvensis is a troublesome agricultural weed and occurs in especially the Orange Free State and the eastern and southern parts of the Cape Province. Biological control may possibly contribute to curbing this weed in South Africa. The eriophyid, Aceria malherbae Nuzzaci, causing deformation and galling on C. arvensis is regarded as one of the most promising candidates for the biological control of this weed. It was imported and successfully established on potted plants in a quarantine laboratory on biotypes of the weed occurring in South Africa. The biology and host specificity of A malherbae are accounted for, by using reported information and data obtained during this study. The biology of A. malherbae broadly conforms to the biology of other eriophyid species. This species has a narrow host range, being restricted to species very closely related to C. arvensis. The symptoms caused by this eriophyid on C. arvensis are described, and seem especially harmful to the reproductive potential of the plant. Two eriophyid species from L. camara from Paraguay, Tegonotus stefneseri and Paraphytoptus magdalenae, are described as new species. An illustrated as well as a dichotomous key to species (Eriophyoidea) described from L. camara, including the two new species, are provided. A key, and a review of known Tegonotus species, incorporated in a compendium based on the original descriptions of 74 species, are included. Shevtchenkella Bagdasarian is considered to be a junior subjective synonym of Tegonotus Nalepa.

D.Sc. (Botany) / Please refer to full text to view abstract

Thesis (MScConEcol)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The role of mites as primary vectors of various fungi within Protea infructescences was recently confirmed and raised questions about their general diversity and their role within this unique niche. Although mites evidently form an integral part of Fynbos ecosystems and probably play a significant role in Protea population dynamics, there is a general void in our knowledge of mite diversity within the Cape Floristic Region. These organisms do not only affect ecological processes within the CFR, but also the economic value of Protea exports. This study sets out to describe mite communities within the infructescences of a variety Protea species. In the process, the role of various environmental variables and differences in host characteristics affecting these communities are also explored. A total of 24281 mite individuals, comprising of 36 morphospecies in 23 families, were collected from 16 surveyed Protea spp. Mite community structure and composition were significantly influenced by plant taxonomy, phenology and infructescence architecture in different Protea spp. At a temporal scale, infructescence age and season were influential factors on mite community structure. Collection locality significantly influenced mite communities within the infructescences of a single Protea sp. Host architecture had no influence on mite communities within a single host species. Geographic distance had no significant influence on mite community structure within Protea infructescences. This implies that factors particular to particular host species determine mite communities. These include factors such as the mode of pollination of the host plant, level of serotiny and plant life form. Numerous newly recorded mite species collected from Protea infructescences are also described in this study. An identification key to the Tydeidoidae of South Africa is provided here for the first time. This study forms a baseline dataset for future studies on the biodiversity of mites in this extremely diverse eco-region. / AFRIKAANSE OPSOMMING: Die rol van myte as primêre vektore van verskeie funguses binne Protea vrugtekoppe is onlangs bevestig, en het vrae laat ontstaan oor hulle algemene diversiteit en rol binne hierdie unieke nis. Alhoewel myte duidelik ‘n integrale deel vorm van Fynbos ekosisteme en waarskynlik ‘n belangrike rol speel in Protea populasie-dinamika, is daar ‘n algemene leemte in ons kennis van mytdiversiteit binne die Kaapse Floristiese Ryk (KFR). Hierdie organismes affekteer nie slegs ekologiese prosesse binne die KFR nie, maar ook die ekonomiese waarde van Protea-uitvoere. Hierdie studie mik as vertrekpunt om die verkillende myt-gemeenskappe binne die vrugtekoppe van verskeie Protea spesies te beskryf. In die proses is die rol van verskillende omgewingsveranderlikes en verskille in gasheer kenmerke wat hierdie gemeenskappe affekteer, ook ondersoek. ‘n Totaal van 24281 myt individue, saamgestel uit 36 morfspesies in 23 families, mytgemeenskappe is beduidende beinvloed deur die taksonomie van die plant, die fenologie en die vrugtekop-argitektuur van verskillende Protea spesies. Op ‘n temporale skaal is gevind dat vrugtekop-ouderdom en seisoen beduidende faktore is in die samestelling van mytgemeenskapstruktuur. Versamel-lokaliteit het verder mytgemeenskappe binne die vrugtekoppe mytgemeenskappe binne ‘n enkele gasheerspesie getoon nie. Geografiese afstand het geen beduidende invloed op mytgemeenskapstruktuur binne Protea vrugtekoppe getoon nie. Dit faktore in soos die metode van bestuiwing van die gasheer plant, die vlak van saadhoudendheid van die Protea koppe en plant-lewensvorm. Verskeie nuwe myt spesies wat uit Protea vrugtekoppe versamel is, word ook in hierdie studie beskryf. ‘n Identifikasie-sleutel vir die Tydeidoidae van Suid-Afrika word verder vir die eerste keer hier verskaf. Hierdie studie vorm die basis datastel vir toekomstige studies van die biodiversiteit van myte in hierdie besonder diverse eko-omgewing.

Water hyacinth (Eichhornia crassipes) is an aquatic macrophyte originating from the Amazon basin. Due to its beautiful appearance it has been introduced into numerous countries across the world as an ornamental pond plant. It was introduced into South Africa in the early 1900s and has since reached pest proportions in many of the country’s fresh water bodies, causing significant economic and ecological losses. It is now considered to be the worst aquatic weed in South Africa. Efforts to control the spread of the weed began in the early 1970s and there have been some successes. Biological control has been used widely as an alternative to mechanical and chemical controls because it is cost-effective, self-sustaining and environmentally friendly. To date, six biological control agents have been introduced onto water hyacinth in South Africa. However, due to factors such as cold winter temperatures and interference from chemical control, the agent populations are occasionally knocked-down and thus the impact of biological control on the weed population is variable. In addition, many South African water systems are highly eutrophic, and in these systems the plant growth may be accelerated to such an extent that the negative impact of the agents’ herbivory is mitigated. One of the agents established on the weed is the galumnid mite Orthogalumna terebrantis, which originates from Uruguay. In South Africa, the mite was initially discovered on two water hyacinth infestations in the Mpumalanga Province in 1989 and it is now established at 17 sites across the country. Many biological control researchers believe that the mite is a good biological control agent but, prior to this thesis, little quantitative data existed to confirm the belief. Thus, this thesis is a post-release evaluation of O. terebrantis in which various aspects of the mite-plant relationship were investigated to determine the efficacy of the mite and thus better understand the role of the mite in the biological control programme of water hyacinth in South Africa. From laboratory experiments, in which mite densities were lower than densities occurring in the field, it was found that water hyacinth growth is largely unaffected by mite herbivory, except possibly at very high mite densities. When grown in high nutrient conditions the growth of the plant is so great that any affect the mite has is nullified. Plant growth is thus more affected by nutrients than by mite herbivory. However, mite feeding was also influenced by water nutrient levels and mite herbivory was greatest on plants grown in high nutrient conditions. The presence of the mite had a positive effect on the performance of the mirid Eccritotarsus catarinensis, such that the interactions of the two agents together had a greater negative impact on the plant’s growth than the individual agents had alone. Furthermore, water hyacinth physiological parameters, such as the plant’s photosynthetic ability, were negatively impacted by the mite, even at the very low mite densities used in the study. Plant growth rate is dependent on photosynthetic ability i.e. the rate of photosynthesis, and thus a decrease in the plant’s photosynthetic ability will eventually be translated into decreased plant growth rates which would ultimately result in the overall reduction of water hyacinth populations. In addition, temperature tolerance studies showed that the mite was tolerant of low temperatures. The mite already occurs at some of the coldest sites in South Africa. Therefore, the mite should be able to establish at all of the water hyacinth infestations in the country, but because it is a poor disperser it is unlikely to establish at new sites without human intervention. It is suggested that the mite be used as an additional biological control agent at sites where it does not yet occur, specifically at cold sites where some of the other, less cold-tolerant, agents have failed to establish. Finally, conditions of where, how many and how often the mite should be distributed to water hyacinth infestation in South Africa are discussed.