Masters Degrees (Entomology)

Permanent URI for this collectionhttps://hdl.handle.net/10413/7535

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Ant diversity, assemblage composition and other arthropod activities in relation to the invader Parthenium hysterophorus L. (Asteraceae) and its biological control agent.
(2022) Hlabisa, Fanelesibonge Samkele.; Munyai, Thinandavha Caswell.; Strathie, Lorraine W.
Invasive alien plants have the potential to alter ecosystem function. While a growing number of studies have focused on the effects of invading plants on native biodiversity and the underlying community dynamics, there is still a lack of studies that detail the impact of invasive plants, such as Parthenium hysterophorus L. (Asteraceae), at higher trophic levels. This study investigated whether P. hysterophorus and its biological control agent, the stem-boring weevil Listronotus setosipennis (Hustache) Coleoptera: Curculionidae, affected ant diversity, assemblages and arthropod activities in the KwaZulu-Natal and Mpumalanga provinces of South Africa. The objectives of this study were to assess the impacts of P. hysterophorus invasion and presence of L. setosipennis on the diversity and assemblage composition of ants, a dominant terrestrial group. Additionally, whether vegetative variables in habitats invaded by P. hysterophorus affected ant assemblages, was examined. Lastly, the study investigated the impacts of the presence and absence of L. setosipennis on other arthropod activities. To study ant diversity and assemblage composition, ants were collected using pitfall traps, over five sampling periods from December 2019 to March 2020, in nine locations around KwaZulu- Natal and Mpumalanga provinces. At each site, three treatments were sampled; viz. P. hysterophorus invaded habitat, P. hysterophorus invaded habitat with L. setosipennis present, and habitat without P. hysterophorus. Species richness and abundance were compared between treatments using ANOVA and the Post-hoc Turkey test. Assemblage composition was analyzed using non-metric multidimensional scaling (NMDS). A Canonical Correspondence Analysis (CCA) was also used to correlate the best environmental variable with ant diversity and assemblage composition. Some 16 463 ant specimens that were collected were identified from four subfamilies, 27 genera, and 55 species. Results indicated that the presence of P. hysterophorus and its biological control agent L. setosipennis did not significantly alter ant diversity, as indicated by species richness and abundance, and assemblage composition, although some differences occurred across locations. The results also showed that vegetative variables (P. hysterophorus height, flowering and cover) did not significantly influence ant assemblages. A separate experiment at six locations in KwaZulu-Natal and Mpumalanga provinces, arthropod activities on P. hysterophorus plants were studied during timed observations at 07h00, 10h00 and 12h00 during monthly sampling from December 2020 to March 2021. Although some arthropod groups were less common visitors to P. hysterophorus than others, this study showed that the presence of L. setosipennis had no significant effect on overall arthropod activities. However, results demonstrated greater activity for some arthropod groups, specifically Hymenopterans, in both treatments, accounting for 60% of all arthropods recorded. Other studies have reported either a positive or negative impact on arthropods by invasive alien plants. These plants may provide a better food resource for native insects and other arthropods, causing them to be attracted to them. However, invasive alien plants have also been linked to a decline in invertebrate species diversity or changes in the composition of populations. This study contributed to growing knowledge on the impacts of invasive alien plants and on terrestrial arthropods, the most prominent group of invertebrates, that are also known to be significant indicators of biological change.
Biology, seasonal abundance and host range of capitulum-feeding insects associated with the invasive weed Senecio madagascariensis (Asteraceae) in its native range in KwaZulu-Natal, South Africa.
(2021) Mkhize, Nokwanda Lady-Fair.; Olckers, Terence.; Egli, Daniella.; Willows-Munro, Sandi.
Native to KwaZulu-Natal, South Africa, Senecio madagascariensis (fireweed) is a herbaceous plant that has become highly invasive in many countries where it was accidentally introduced in contaminated fodder. Rapid growth rates, high fecundity and toxic secondary compounds that poison livestock have caused severe economic impacts in infested pastures and rangelands. Biological control, using imported natural enemies from South Africa, is being pursued as a long-term control option for invaded countries, particularly Australia where invasions are most severe. This study forms part of a collaboration with the CSIRO in Australia to source and assess potential insect biocontrol agents that could be imported into Australia. The aims of this study were to: (i) investigate and identify species of capitulum-feeding insects on fireweed populations; (ii) determine the seasonal abundance of capitulum-feeding insects on fireweed populations in the field; (iii) differentiate between the different lepidopteran and dipteran species associated with fireweed by means of DNA barcoding; and (iv) verify the host range of these insects by surveying related Senecio species in the field and comparing the associated insects using DNA barcoding. Insects with capitulum-feeding larvae included Coleoptera, Lepidoptera and Diptera and were most abundant during late summer and autumn. The most important potential biocontrol agents were the lepidopterans Homoeosoma stenotea (Pyralidae) and an unidentified species of Platyptilia (Pterophoridae), while the flies, which included two unidentified species of Trupanea (Tephritidae), were less abundant. DNA barcoding of the COI gene revealed distinct genetic lineages (possible species) of lepidopterans that were recorded on eight of the 36 surveyed Senecio species, with most specimens conforming to H. stenotea and Platyptilia sp. Homoeosoma stenotea was recorded on three, and Platyptilia sp. on one, non-target Senecio species, respectively. The species of Trupanea were restricted to S. madagascariensis, but since they were collected only during seasonal surveys, studies of their host specificity were not concluded. Since the two lepidopteran species do not appear to be strictly host specific, they may not be suitable biocontrol agents for countries like Australia that have a diverse native Senecio flora. However, countries that lack native or economically important Senecio species may choose to further consider these potential agents.
The ecology and ethology of ball-rolling dung beetles (Coleoptera: Scarabaeidae)
(1976) Tribe, Geoffrey Darryl.; Fietcher, D. J. C.; Crewe, R. M.
Abstract available in PDF.
Ant communities along an elevational transect, the Udzungwa Mountains in Tanzania.
(2020) Kunene, Caroline.; Munyai, Thinandavha Caswell.; Foord, Stefan Hendrik.
Understanding biodiversity patterns and the processes that structure them along environmental gradients has been a topic of major ecological interest. Although relatively well-known, alpha diversity is still poorly understood. It is therefore crucial to investigate alpha diversity patterns as they reveal how diversified species are within a site and identifies processes underlying the co-occurrence of species at a local scale. The patterns and processes related to beta diversity, however, have lagged even more behind. Beta diversity describes the variation in species composition between sites. It reveals whether species turnover or richness differences cause variation in community composition between sites. Together, alpha and beta diversity may provide baseline information for conservation planning, especially in African Tropics. African tropical rainforests, although very diverse, are some of the most threatened and understudied ecosystems of the world. Similarly, although the primary aim in ecology has been to document biodiversity patterns and the processes that structure them, those of invertebrates have lagged behind. As a result, very little is known about African tropical invertebrate patterns and the mechanisms that drive them. The current study, therefore aims (1) describe ant diversity patterns and community assemblages along the Udzungwa mountains, (2) to describe the extent of compositional differences between sites (beta diversity) and (3) to reveal the assembly mechanisms that drive these differences along an altitudinal gradient, Udzungwa Mountains, Tanzania. A standardized pitfall survey was conducted across five elevational transects, each at a distance of 0.1, 1, 20 and 174 km from the first one. Three target elevations which correspond to the three forest types of this mountain (lowland (300-800 m.a.s.l), sub-montane (800-1400), montane (1400-1500)) were selected. A total of 31 776 ant specimens were collected. They belong to five subfamilies, 34 genera and 101 species. Species richness declined with increasing elevation. Three species assemblages corresponding to the three forest types were observed across the mountains. The lowland assemblage was very distinct, while the sub-montane and montane assemblages were closely related. Results show that distance (km) and elevational distance (m.a.s.l) influence variation in community composition (beta diversity). Beta diversity increases with geographic and elevational distance, although more noticeable with elevation. The standardised effect sizes (SES) models suggest that species turnover increases with distance and elevation, while richness differences decrease with distance and elevation. Species turnover plays a significant role in structuring ant communities with increasing elevation while neither species turnover nor richness differences play a significant role in structuring ant communities with increasing geographical distance. The overall findings of this study, therefore, suggest that ants of the Udzungwa mountains are niche conservative, beta diversity is affected by distance and elevation and that species replacement structures ant communities with increasing elevation, while biotic interactions structure ant communities with increasing distance. Therefore, temperature is very important in structuring ant communities along the Udzungwa mountains and complementarity between sites is maximized by choosing sites that are at different elevations.
Ant diversity and composition in a reforested landscape of Buffelsdraai Landfill Conservancy, KwaZulu-Natal.
(2019) Xolo, Sbongiseni.; Munyai, Thinandavha Caswell.; Slotow, Robert Hugh.; Foord, Stefan Hendrik.
Restoration of degraded and reclaimed landscapes provide a useful framework to evaluate the recovery of biodiversity loss. A reforestation project was initiated in 2008 by eThekwini Municipality in Buffelsdraai Landfill Conservancy, aiming to offset carbon emissions over a 20-year period and increase climate change adaptation through biodiversity and ecosystem services restoration. The project offered an opportunity to evaluate to what extent reforestation for carbon sequestration can have co-benefits for biodiversity. The current study monitors the recovery of habitat restoration practices (planting of indigenous forest trees) in Buffelsdraai Landfill Conservancy, eThekwini Municipality, KwaZulu-Natal Province, in South Africa. The main aim of the study was to evaluate how biodiversity recovers following forest restoration. The study used ants (Formicidae: Hymenoptera) as a model organism as they comprise a significant component of invertebrate diversity and a keystone taxon in the terrestrial ecosystems. The study objectives were to provide ant checklist in a reforested landscape and to describe ant diversity patterns along a gradient of restoration and to identify the environmental variables which drive the diversity patterns along a reforestation gradient. Using a standardized pitfall survey, ants were sampled across eight sites, each replicated four times, which included sugarcane (unrestored), grassland and scarp forest (natural reference sites), short-term (0-2 year), medium-term (3-5 years) and long-term (6-8 years) restored sites. Ant sampling was conducted in April-May 2017 (early dry season) and December 2017 (wet season). Environmental (habitat structure) and soil surveys were conducted at each plot. A total of 27 439 ant specimens comprising of 96 species in 31 genera, and six subfamilies were collected. Sample coverage estimator was larger than 0.97, indicating that inventory completion approximated most of the ant assemblages found in the study area. Myrmicinae, Ponerinae and Formicinae were the most abundant and species-rich subfamilies, with Tetramorium, Pheidole and Monomorium as the most species-rich genera. The most numerically dominant species were Pheidole megacephala species group and Anoplolepis custodiens. Ant species richness and activities were significantly highest in the restored and grassland sites and low in forest site, and lowest in unrestored sugarcane. Species richness responded with a hump-shaped response as patterns of species richness significantly decreased with increasing bare-ground cover. High species diversity and composition was associated with open habitats with grass layer. Forest had the most distinct assemblages. Leaf litter, vegetation structure, canopy cover and bare-ground cover, were the four predictor variables which had major influences on ant assemblage structure. Four forest indicator taxa were identified (Pheidole UKZN_11 (megacephala gp.), Tetramorium UKZN_04 (squaminode gp.); Tetramorium UKZN_28 (setigerum gp.) and Leptogenys attenuate), and one indicator for grassland (Lepisiota capensis). No indicators were found for sugarcane sites. Solenopsis UKZN_01 and Pheidole UKZN_09 were potential indicator for restored sites. The restoration sites were transitioning from sugarcane plantation, and were drawing most of their colonisation from grasslands at this stage. This study shows that open woodlands are ideal habitats for maximising species diversity, as they provide a complex habitat for many species, and the availability of local natural grassland as a source of invertebrates assists restoring functioning, even if we expect the community to transition to forest species as regrowth progresses.
An investigation into the robustness of insectary-reared Anopheles Arabiensis for use in the Sterile Insect technique for controlling malaria.
(2018) Manilal, Yurita Yona.; Olckers, Terence.; Maharaj, Rajendra.
Human malaria is one of the deadliest vector-borne diseases in the world and is caused by parasites of the genus Plasmodium that are transmitted via mosquitoes of the genus Anopheles. The highest impact of malaria can be seen in Africa, where 90% of worldwide deaths occur. Although current vector control strategies include biological control, chemical application and environmental management, there is renewed interest in the Sterile Insect Technique (SIT). SIT involves the mass production of the target population, in this study Anopheles arabiensis Patton, sterilizing the males with ionizing radiation and, thereafter, the mass release of these sterile males into the natural environment. The subsequent mating of the sterile males with the wild females should result in a decrease, and ultimately the elimination, of the natural An. arabiensis population. However, for SIT to be successful, the insectary-reared males need to compete effectively with their wild counterparts for female insemination. This study was conducted to determine if the laboratory-reared males would be able to compete successfully with the wild male population in northern KwaZulu-Natal. Standard testing protocols were taken from the Malaria Research Unit, World Health Organization, as well as methods proposed by the National Health Laboratory Services. The collection of mosquitoes from the target area indicated that An. arabienis is a seasonal species with populations increasing during warmer conditions. The mating compatibility between the three tested strains of An. arabiensis, namely the Old Mamfene strain (laboratory strain), New Mamfene Strain (wild strain) and the Genetic Sexing Strain, proved favorable due to statistically non-significant insemination rates. However, the results indicated that the laboratory-reared colony displayed greater fecundity and mean numbers of larvae hatched than the wild colony. Within strains, overcrowding of larvae affected the size of the male adults, although reduced size did not affect mating within each strain, as insemination rates were not statistically affected (p>0.05). Dyes were tested to track mating between sterile males and wild females. However, dye transfer from male to female during copulation resulted in mating compatibility being negatively affected. Further investigations are thus needed to determine a better approach to tracking females that have copulated with released males. Although the results indicate that laboratory-reared males can compete successfully with their wild counterparts, field studies are required to verify these laboratory results.
The impact of soil water and nitrogen variability on the fitness and performance of Neolema abbreviata Larcordaire (Chrysomelidae) a biological control agent for Tradescantia fluminensis.
(2018) Mbande, Abongile.; Chidawanyika, Frank.; Tedder, Michelle Jennifer.
Tradescantia fluminensis Vell. (Commelinaceae) is a plant of Neotropical origin native to the southern parts of Brazil bordering Argentina. In South Africa, it is classified as a category 1B invader species in the National Environmental Management Biodiversity Act (NEMBA) owing to its incipient phase of invasion. The occurrence of naturalised populations of T. fluminensis has so far been confirmed in all provinces except the Free State, Northern Cape and North West. In cognisance of the devastating effects of invasive alien plants on native biodiversity, ecosystem health and ultimately provision of ecosystem services, several control methods have been employed with varying degrees of success. Classical biological control, which involves the release of exotic natural enemies (pathogens and herbivorous insects), is one such method widely-used because of its relatively low costs and minimal non-target effects. For T. fluminensis, Neolema abbreviata (Larcodaire) Coleoptera: Chrysomelidae) is one agent that is earmarked for release in South Africa following a successful introduction in New Zealand. However, little is known how novel environments presented by soil water and nutrient gradients may indirectly influence its herbivore performance and life-history through alterations in host-plant quality. In this era of global climate change where anthropogenic activities have led to changes in rainfall patterns and biogeochemical cycles of major elements such as nitrogen, investigation of species responses to such is important. Results from my study show that both water and nitrogen (N) variability influenced plant biomass accumulation, foliar N content and subsequent herbivore performance, and life-history traits of both adult and larval N. abbreviata. The longest vines were on plants that had optimal irrigation under excess fertiliser whilst severely water stressed plants that had excess fertiliser had the shortest vines. Foliar N content was highest in plants that had excess fertiliser under both pulsed and optimal irrigation whilst lowest foliar N content was in plants under optimal irrigation without any fertiliser. Optimally irrigated plants that received moderate fertiliser had their highest rate of egg deposition in both no-choice and multi-choice conditions suggesting quality-based host ranking behaviour in N. abbreviata. The consequent larval performance traits which included weight gain and time to pupation were superior in this treatment thereby providing support for the preference-performance hypothesis (PPH). Feeding patterns between larvae and adults among plant treatments were largely similar suggesting uniform nutritional requirements across the life-stages. There were limited parental effects of plant quality on the life-history traits in both larvae and adults across F1 and F2 generations. In reciprocal diet transplant experiments, there were no significant responses to parental diet effects on larval weight, mortality, feeding damage, pupal weight and days to pupation. However, there were significant parental diet x test diet interactions with offspring from parents fed on high N plants generally performing better on low N test plants in traits such as larval weight gain and final pupal weights. Oviposition selection, feeding weight and longevity did not respond to the effects of parental diet nor its interaction with test diet, unlike the case with larval traits. There were significant correlations between pupal weight and number of days to pupation, pupal weight and eclosion success. I conducted a 3 x 3 full factorial experiment to determine the impact of water and fertiliser variability on the performance of Neolema abbreviata (and its host plant Tradescantia fluminensis. My results show differential responses to parental diet between larvae and adults of the same generation among an insect species with both actively feeding larval and adult life-stages. However, there was no correlation between adult weight and longevity. Overall, my thesis contributes to the growing body of literature on the impacts of anthropogenic global change on plant-insect interactions. It will also assist land managers when applying biological control of T. fluminensis. Furthermore, my results show the implications on the successful biological control (mass-rearing and field release) of T. fluminensis resulting from variable nitrogen and water conditions.
Aspects influencing the suitability of Rhizaspidiotus donacis (Leonardi) (Hemiptera: Diaspididae), a candidate biological control agent for the invasive giant reed, arundo donax L. (Poaceae) in South Africa.
(2016) Pillay, Sasha-Ann.; Olckers, Terence.; Bownes, Sarah Jane.
Abstract available in PDF file.
Development of Beauveria brongniartii as a bio-insecticide to control white grub (Coleoptera: Scarabaeidae) species attacking sugarcane in South Africa.
(2016) Kheswa, Nozipho.; Conlong, Desmond Edward.; Laing, Mark Delmege.; Shuttleworth, Adam.
Abstract available in PDF file.
Monitoring the spread of Sirex noctilio in pine plantations in South Africa (2004 – 2014).
(2016) Croft, Philip Kenneth.; Olckers, Terence.; Light, Marnie Elizabeth.
Abstract available in PDF file.
Distribution and seasonal abundance of the flowerbud weevil anthonomus santacruzi hustache (coleoptera: curculionidae) in KwaZulu-Natal and its impact on the invasive weed solanum mauritianum scopoli (solanaceae).
(2016) English, Kelby Farrell.; Olckers, Terence.
Solanum mauritianum Scopoli (Solanaceae), native to South America, is an invasive weed of tropical, subtropical and warm temperate regions in many countries including South Africa. The seed-packed fruits are highly palatable to native birds which feed on them throughout the year, vastly aiding in the weed’s dispersal. Research into the biological control of the weed began in the 1980s after chemical and mechanical control efforts proved insufficient and resulted in the release of Gargaphia decoris Drake (Hemiptera: Tingidae), a leaf-sucking lace bug, in 1999. Anthonomus santacruzi Hustache (Coleoptera: Curculionidae), a flowerbud weevil, was later released in 2008 to reduce the excessive levels of fruiting by S. mauritianum populations. Although several thousand weevils have recently been released in KwaZulu-Natal province, where infestations of S. mauritianum are particularly severe, to date there has been no post-release evaluation to determine the extent of the weevil’s establishment, seasonal abundance and impact on the weed’s reproductive output. Twenty four sites with healthy populations of S. mauritianum were initially sampled in the KwaZulu-Natal midlands and coastal regions from February to October 2014 to determine the presence and abundance of A. santacruzi. Populations of A. santacruzi were recovered at 14 sites, mainly along the coast, with poor establishment recorded in the inland region. A preliminary assessment of the role of climate in the weevil’s establishment suggested that low temperatures may be a constraint. Six sites (three inland and three coastal) with established populations of A. santacruzi were subsequently chosen for monitoring across seasons from October 2014 to September 2015. Although seasonally variable, the numbers of flowers and flowerbuds of S. mauritianum were high at all sites throughout the monitoring period, indicating no distinct periods of food scarcity. However, the numbers of weevils were relatively low in comparison resulting in low levels of floral damage (up to 26%) and no apparent impact on fruiting. Although higher weevil numbers were recorded at the coastal sites, there was a consistent trend of weevil numbers peaking during the autumn months (April/May), at all six sites. Despite the low population densities of A. santacruzi, there were indications of density-dependent relationships between food availability and weevil numbers. At the study sites (i.e. where A. santacruzi had established), climatic factors (e.g. monthly temperature) had no significant effect on the abundance of the weevils. Ants were frequently associated with S. mauritianum inflorescences at the study sites and displayed a significant positive relationship with the numbers of mature fruits, presumably because of their high sugar content. However, there was no relationship between weevil abundance and the numbers of ants, suggesting that ants were not interfering with the weevil populations. A preliminary survey for parasitoids failed to provide any evidence that the weevil’s immature stages had recruited native parasitoids. Only seven years has elapsed since A. santacruzi was first released in KwaZulu-Natal. Although the weevil’s establishment and population proliferation has been confirmed at several sites, its impact on S. mauritianum populations is currently negligible. Should higher population densities of A. santacruzi be realized over the medium to longer term, its impact could become significant. Further monitoring of A. santacruzi populations should thus be conducted in KwaZulu-Natal, but also in other provinces, to determine their potential for the biocontrol of S. mauritianum. Keywords: Agent establishment, bugweed, flowerbud-feeding agents, resource availability, seasonal abundance, weed biological control.
Aspects influencing the efficacy of Liothrips tractabilis Mound and Pereyra (Thysanoptera: Phlaeothripidae): a biological control agent for the invasive weed Campuloclinium macrocephalum (Less.) DC. (Asteraceae) in South Africa.
(2015) Ramanand, Hiresh.; Olckers, Terence.; McConnachie, Andrew.
Pompom weed, Campuloclinium macrocephalum (Less.) DC. (Asteraceae), an unpalatable, perennial, erect invasive herb from South America has become naturalized in South Africa, invading grasslands, savannas and wetlands, where it has a significant impact on biodiversity. In order to sustainably curb the spread and negative impact of the weed, Liothrips tractabilis Mound and Pereyra (Thysanoptera: Phlaeothripidae) was imported from South America (Argentina) as a candidate biological control agent. Quarantine tests demonstrated that the thrips was suitably host specific and damaging to the target weed and permission for its release in South Africa was granted in 2013. However, numerous biocontrol agents worldwide have displayed exceptional potential while in quarantine but have had little to no success following their release in the field. This study incorporated both laboratory and field trials to determine the likelihood of success with the thrips. Liothrips tractabilis developmental threshold trials were conducted at seven constant temperatures (15, 17.5, 20, 25, 27.5, 30, 32°C) and the data, excluding the uppermost and lowermost temperatures (as the trips did not survive at these temperatures), were ultimately used to develop a degree-day model. The findings of the model were then validated under outdoor conditions. Furthermore, the impact of the thrips was assessed on seedlings and root crown regrowth shoots under outdoor conditions, and the results were compared to those of the laboratory impact trials that were conducted while the agent was still under investigation in quarantine. The thrips completed development at all five temperatures, with the number of days taken to develop from egg to adult decreasing with increasing temperature. Lethal temperatures were recorded at 15°C and 32.5°C where no development beyond the egg stage was observed. The lower developmental threshold (t) was estimated at 9.6°C with 546.9 degree-days (°D) required by the thrips to complete its development. The degree-day model predicted that in Gauteng, parts of Limpopo, North West and Mpumalanga provinces, where C. macrocephalum is invasive, the thrips is likely to complete 3-9 generations per year. The outdoor developmental trials did validate the model and although temperatures recorded in the laboratory and field trials were not equal, the field data largely supported the predictions of the laboratory trials. Furthermore, the thrips developed significantly faster at the Pietermaritzburg site in comparison to Cedara, which was largely a consequence of low altitude and higher ambient temperatures. A significant difference was also obtained across the three seasons, where the thrips developed fastest during summer, and slowest during winter at Pietermaritzburg. The same was true at Cedara, although no development occurred during the winter trials. The impact trials showed that the thrips significantly reduced the height, number of leaves and both wet and dry masses of C. macrocephalum seedlings, which was largely in agreement with the original laboratory study. However, this was not the case with the regrowth trials, where only relative growth rates in terms of wet tuber mass were significantly reduced by thrips feeding. These results were largely a consequence of varying tuber wet masses used at the start of the trials. Liothrips tractabilis appears to be climatically compatible with conditions in South Africa, since this study has shown that the establishment and persistence of L. tractabilis is unlikely to be limited by climatic conditions in areas that are currently invaded by the target weed. Furthermore, the agent should be able to inflict appreciable damage and hence have an impact on C. macrocephalum populations in the field. Thus, prospects for the biological control of C. macrocephalum in South Africa appear promising.
Impact of the biological control agent Aceria lantanae (Cook) (Acari: Trombidiforms: Eriphyidae) on the invasive weed Lantana camara L. (Verbenaceae) in South Africa.
(2015) Mukwevho, Ludzula.; Olckers, Terence.
This study was conducted to determine the establishment, dispersal, performance and impact of a recently introduced flower-galling mite, Aceria lantanae (Cook) (Acari: Trombiformes: Eriophyidae) on the inflorescence and seed production of the invasive Lantana camara L. (Verbenaceae) in Limpopo, Mpumalanga, Gauteng and KwaZulu-Natal provinces of South Africa. The climate-matching programme CLIMEX was used to predict the distribution range of the mite on the African continent. Furthermore, the influence of some climatic factors (i.e., elevation, temperature, rainfall and relative humidity) and the suitability of different L. camara varieties were also investigated. Aceria lantanae established and persisted for more than 12 months at 58.6% of the release sites in Limpopo, Mpumalanga, Gauteng and KwaZulu-Natal provinces. Continuous surveys also showed that the mite had dispersed widely throughout the geographic range of L. camara in South Africa and Swaziland, with the highest dispersal rate of 40.6 km per annum recorded between the inland area of Nkwene (Swaziland) and the coastal area of Ncotshane (KwaZulu-Natal). The performance of A. lantanae varied among sites, provinces and seasons, with the infestation levels ranging from 2.7% to 97% per site. Inflorescence and seed production declined significantly by up to 86% and 96%, respectively, on lantana stands that were infested with A. lantanae in KwaZulu-Natal compared to the control stands. The CLIMEX model predicted that the climatic conditions for A. lantanae would range from suitable to highly suitable within the distribution range of L. camara in southern Africa. Although not statistically significant, there was a slight decline in A. lantanae infestation levels, with increasing elevation and annual rainfall. Infestation levels were somewhat higher at sites receiving between 600 and 1000 mm of rainfall per year, and decreased slightly as the annual rainfall exceeds 1000 mm. This study also found that infestation levels of A. lantanae were neither related to temperature nor relative humidity. Mite infestations differed significantly amongst the 10 tested varieties of L. camara. Highly preferred varieties included 017 Orange Red, 021 White Pink and 018 Dark Pink, with infestations ranging from 50.4% to 61.2%. Those which were moderately attacked by A. lantanae included 163 Light Pink, 021 Total Pink, 165 Light Pink, 015 Yellow White, 021 Pink and 015 White Yellow varieties, with infestations ranging from 7.8% to 21.4%. Variety 010 Dark Pink was completely rejected by the mite, with no infestations recorded during the study period. Furthermore, regression analysis showed that neither plant size nor inflorescence density influenced A. lantanae infestation levels. However, there was a significant increase in A. lantanae infestation on plants already infested by other lantana biocontrol agents. This study concluded that amongst all investigated parameters, varietal resistance was the major factor that influenced the sporadic establishments and overall performance of A. lantanae throughout the distribution range of L. camara in South Africa.
Suitability of the defoliating beetle Physonota maculiventris (Coleoptera: Chrysomelidae) for release against Tithonia diversifolia (Hemsl.) A. Gray (Asteraceae) in South Africa.
(2015) Mphephu, Tshililo Emmanuel.; Olckers, Terence.; Simelane, D. O.
This study was conducted to assess the suitability of the defoliating beetle Physonota maculiventris Boheman (Coleoptera: Chrysomelidae: Cassidinae) for release as a biological control agent against Mexican sunflower, Tithonia diversifolia (Hemsl.) A. Gray (Asteraceae), in South Africa. The biology and host range as well as the potential impact and distribution of P. maculiventris were studied under quarantine conditions to determine its safety and effectiveness. Under favourable conditions, females laid 5.3 ± 0.3 (mean ± SE) egg batches during their lifetime, with each batch consisting of approximately 33 eggs. Larvae are highly gregarious as early instars and both larvae and adults feed voraciously, often defoliating the plants completely. The life cycle of the beetle was completed in 67.5 ± 7.5 days under quarantine conditions. Among the 58 test plant species subjected to no-choice tests, P. maculiventris developed successfully on T. diversifolia but on very few non-target species. However, only minor damage was recorded on non-target species, notably the exotic weed Xanthium strumarium L. and some sunflower (Helianthus annuus L.) cultivars. Also, survival to adulthood was considerably lower on sunflower cultivars than on the target weed during these tests. During choice tests, P. maculiventris oviposited and developed successfully on T. diversifolia only, with minor feeding damage on some H. annuus cultivars, suggesting that the beetle’s field host range will be confined to the target weed. Risk analysis also showed that P. maculiventris presents an extremely low risk to non-target plant species, notably those within the tribe Heliantheae and other close relatives. The effectiveness of P. maculiventris was assessed on the basis of its impact on the growth and biomass production of the weed. Significant foliar damage by the adult and larval stages of P. maculiventris was recorded at low and high insect densities, causing a 50.2 % and 55.0 % reduction in plant biomass, respectively. Climatic modelling (CLIMEX) suggested that the beetle is likely to establish over the entire range of T. diversifolia in South Africa and neighbouring countries. The study concludes that P. maculiventris is safe for release and is likely to become widely established and cause significant damage to populations of T. diversifolia in South Africa. An application to release P. maculiventris into the field is thus being prepared for submission to the relevant South African regulatory authorities.
Field ecology and impact of the seed-feeding beetle Acanthoscelides macrophthalmus, a biological control agent of the invasive tree Leucaena leucocephala, in the KwaZulu-Natal coastal region.
(2014) Sharratt, Morag Elizabeth Jessie.; Olckers, Terence.
Introduced for agroforestry, the Mexican tree Leucaena leucocephala (Fabaceae) has become invasive in several tropical and subtropical regions worldwide. In South Africa, the most notable infestations are located in the KwaZulu-Natal (KZN) coastal region. A seed-feeding beetle, Acanthoscelides macrophthalmus, originally imported from Mexico, was released in South Africa to control the plant’s excessive seed production and has become widely established in the KZN coastal region. By sampling plant populations monthly at selected field sites in this region, this study was intended to determine the: (i) seasonal (monthly) abundance of the beetle populations; (ii) levels of seed damage inflicted in relation to seed production by the plants; (iii) extent to which the beetle has recruited native parasitoids; (iv) incidence of non-target effects; and (v) ability of the beetle to regulate/control plant populations or limit their spread. Beetle numbers fluctuated greatly between months and between sites, resulting in erratic levels of seed damage ranging from 2-60%. Although ripe pods were available to the beetles throughout the year at one of the four study sites, this was not the case at the other three sites where ripe pods were virtually absent from November to January. High numbers of undamaged seeds found on the soil surface indicated the extent to which the seeds escape beetle predation. Parasitism of the beetle’s larval/pupal stages by native parasitoids was variable and relatively high (up to 40%). Ten species of parasitic wasps were reared from beetle-infested seeds, the most important of which originated from native Acacia plants. There were no instances of non-target effects involving the seeds of native Acacia species. There was a strong positive relationship between wasp numbers and beetle-infested seeds, indicating that the relationship is not incidental, and that the beetle has been adopted by the wasps as a new host. The relationship between the percentage of seeds damaged by A. macrophthalmus and seed availability was inversely density-dependent, with higher rates of seed damage occurring when fewer seeds were available. This negative relationship between seed damage and seed availability, as well as the relatively low levels of seed damage recorded, suggest that the beetle’s impact is negligible. The addition of other seed-feeding or seed-reducing agents to the L. leucocephala system may result in a more significant contribution from A. macrophthalmus.
Molecular diagnostics and phylogenetics of white grubs in sugarcane.
(2008) Dittrich-Schröder, Gundrun.; Conlong, Desmond Edward.; Mitchell, Andrew.
Scarabaeid pests in South Africa and especially KwaZulu-Natal are characterised by a very long larval life cycle and short pupal and adult periods. However, it has nearly always been the adults of the species that have been identified, with very little attention paid to the larval identification of the species. This is unfortunate as it is nearly always the larval stage that is found to be associated with crop damage. Accurate identification of the species of these larvae is important for the management of scarabaeid pest species, as it unlocks the necessary information on the biology and ecology of many species, which allows the adaptation of control methods for different species. Inadequate keys for the taxonomy of larvae of these groups, as well as the lack of morphological taxonomists working on these groups have been identified as constraints. When a species is difficult to identify using traditional taxonomic methods, DNA diagnostic tools can be useful. Chapter 2 investigated the feasibility of identifying scarabaeid larvae using mitochondrial DNA data. Variation in the base pair sequence of the mitochondrial cytochrome c oxidase sub unit I (cox 1) gene was used. DNA sequences of cox 1 from scarabaeid larvae collected from sugarcane fields were compared with sequences from scarabaeid adults of known species in order to identify the species attacking sugarcane. Neighbour-joining and maximum parsimony analyses of 658 bp cox 1 sequences identified groups of larvae that linked to adult specimens. The major groupings delimited specimens belonging to the subfamilies Dynastinae, Melolonthinae and Rutelinae. Within-group sequence divergence ranged from 0 - 3.4 % and divergence between sister groups ranged from 2.6 - 25.1 %. The recorded divergence range within and between tribes was 0 - 21.3 % and 17.3 - 28.5% respectively. Similarly, the divergence range observed within and between genera was 0 - 19.2 % and 17.1 - 25.4% respectively. The maximum sequence divergence observed within subfamilies was 23.7 % and divergence between subfamilies ranged from 16.8 - 26.7 %. Examination of pairwise sequence divergence levels as well as node support allowed 68% of the unidentified larval specimens to be associated with identified adult specimens. Phylogenetic analysis matched identified adult mtDNA with unidentified larval mtDNA. This allowed the identification of those larvae through morphological characteristics unique to certain species. To create a field key to the subfamilies of Dynastinae, Melolonthinae and Rutelinae the most useful character distinguishing larvae of different species was the raster but additional morphological characteristics were included. These relationships between larval and adult scarabaeid specimens from sugarcane were examined using various phylogenetic tools. The data set included a total of 19 morphological characters as well as 166 partial cox 1 gene sequences. Maximum parsimony analyses were performed on morphological, molecular and combined data. The same morphological and molecular data sets were run both separately and as a combined analysis with MrBayes. In both types of analyses the morphological data performed poorly and crude groupings resulted, dividing taxa to tribe level only. Molecular data showed greater resolution than the morphological data and taxa were separated into groups equivalent to species and morphospecies designated in Chapter 2. A partition homogeneity test indicated that both data types could be combined. It is recommended that both morphological and molecular data be utilised in identification of scarabaeid sugarcane pests and that a character-based approach be implemented. Further molecular data from other genes should be included to test the accuracy of these results. The keys produced during this study will allow workers to focus on a single species biology, and subsequently allow an analysis of between species interactions, and within species control. These advances are a start to the improvement of knowledge of the species composition of scarabaeid larvae in sugarcane fields, thus making management and biological control of these pests a greater possibility. Further recommendations for future work are discussed in Chapter 5.
Investigation of the biology and cross-breeding of populations of Pareuchaetes insulata (Lepidoptera : Arctiidae) and the implications for the biological control of Chromolaena odorata (Asteraceae) in South Africa.
(2008) Dube, Nontembeko.; Olckers, Terence.; Zachariades, Costas.
Larvae of Pareuchaetes insulata were released in South Africa for the biological control of the invasive weed Chromolaena odorata. Pareuchaetes insulata has proved to be a difficult agent to establish in the field in South Africa, for various possible reasons. Populations collected from Florida and Jamaica (their aboriginal home) were released separately at several sites each in South Africa, but only one population (Florida) was definitely established. It is possible that adults from this established population interbred with adults from the Jamaican population released at nearby sites. The aims of this study were to determine whether there were any differences in biology between the two populations and whether hybridization affected the fitness of either. Trials involved: (i) pure-breeding of both Florida (F) and Jamaica (J) populations; (ii) cross-breeding of the two populations and; (iii) back-crossing of the hybrids with the parent populations. The fitness of these populations was determined by measuring adult longevity and fecundity, egg viability, and larval development and survival rates. The F population was superior to the J population in most of parameters measured, including fecundity. Hybridization of these populations reduced the fitness of the F population. It is unknown whether these differences in fitness reflect differences in their native regions, laboratory cultures or response to South African C. odorata. It appears that different populations of P. insulata have different levels of fitness, and that hybridization negatively affects the fitness of stronger populations. The lower fitness of the J population may have reduced its likelihood of establishing successfully, and even reduced the fitness of the established F population where the populations came into contact. These results caution that the possible consequences of mixing different genotypes of a biocontrol agent species should be properly investigated prior to their release in the same country.
Thermal physiology and predicted distribution of Zygogramma bicolorata (Chrysomelidae), a promising agent for the biological control of the invasive weed Parthenium hysterophorus in South Africa.
(2008) King, Helen.; Olckers, Terence.; McConnachie, Andrew.; Downs, Colleen Thelma.
Parthenium hysterophorus (Asteraceae), classified as an emerging weed in South Africa, has become abundant throughout large parts of southern and eastern Africa. In South Africa it has invaded areas in KwaZulu-Natal, Mpumalanga, the North West Province and Limpopo. A biological control programme against parthenium weed was launched in South Africa in 2003, based on the success achieved in Australia. Zygogramma bicolorata, a leaf-feeding beetle native to Mexico, was imported into South Africa via Central Queensland, Australia where it was released in the 1980s. This thesis examines aspects of the thermal physiology of Z. bicolorata which, in conjunction with its native and exotic geographical distribution, was used to predict the potential distribution of the agent in South Africa, in relation to climate. To determine Z. bicolorata’s physiological capability, several physiological parameters were examined for mechanistic modelling purposes. These parameters included the beetle’s lethal thermal limits, critical thermal limits, lethal humidities (Chapter 2) and developmental rate at constant temperatures (Chapter 3). In Chapter 4, these physiological parameters were entered into the dynamic modelling program CLIMEX (CLIMEX programme ver. 2, CSIRO Entomology ©) and a map of the areas that are acceptable for the establishment of Z. bicolorata was produced. The CLIMEX model predicted that most of South Africa is favourable for the establishment of the beetle, except in the west of the country and in the north of Lesotho, extending into South Africa. All areas in which parthenium currently occurs were predicted to be very favourable for Z. bicolorata establishment and proliferation. Optimal release sites aimed at initial establishment were earmarked at three areas in the northeastern part of South Africa (Jozini, Ndumu Game Reserve and along the road from Swaziland to Mozambique). It is concluded that Z. bicolorata is climatically suited to South Africa, increasing the likelihood that populations will establish and proliferate when released.
Effect of pyrimethamine on gametocytogenesis, exflagellation and asexual growth in southern African isolates of Plasmodium Falciparum.
(1995) Tsoka, Joyce Mahlako.; Appleton, Christopher Charles.; Freese, Janet Anne.
Pyrimethamine efficacy was investigated in vitro on the blood asexual stages, the sexual stages and exflagellation in Plasmodium falciparum. Gametocytogenesis was stimulated following the standard methods on five isolates of Plasmodium falciparum. From these five isolates, RSA 2, 3 and 5 produced gametocytes which reached maturity within seven days and the gametocytes were able to exflagellate. Isolate MW2 produced young gametocytes which disappeared within ten days. NF54 produced mature gametocytes which lasted for 24 hours only. There were no statistically significant differences between the static and the synchronization methods of gametocyte stimulation for any of the isolates. The effect of pyrimethamine was investigated by adding a known concentration of the drug (For RSA 2, MW2 and NF54, l00nmol/ℓ; RSA 3 and 5, 3000nmol/ℓ pyrimethamine) to the culture medium for seven days during gametocyte stimulation. The results of this investigation show that there was gametocytocidal activity on the isolates that were used and pyrimethamine also had a schizontocidal action on NF54 and the young gametocytes of this isolate were destroyed by the drug. At concentrations which were inhibitory to asexual parasites, the drug had a sporontocidal effect on isolate RSA 2 but not on isolate RSA 5. The pyrimethamine MIC values for asexual parasites ranged from 300nmol/ℓ to > 3000nmol/ℓ (RSA 2 and 5 were not inhibited at 3000nmol/ℓ ). These results are consistent with those found in previous studies when pyrimethamine resistance was first detected in South Africa. The chloroquine MICs indicate a good correlation with the results obtained from previous drug sensitivity tests for all the isolates examined using both the 48-hour in vitro test and isotope incorporation for growth assessment. The isobolograms constructed to determine relationship between chloroquine and pyrimethamine indicated no synergism for isolates RSA 2 and 5, but the Σ relative IC[50]s indicated a weak synergism. Both the isobolograms and the Σ relative IC[50]s for the isolates RSA 6, 9 and 14 indicated an antagonistic action between chloroquine and pyrimethamine. The results obtained from this study have important implications for malaria control in South Africa.
Niche and life-history differences in five highly sympatric species of Trithemis dragonflies (Odonata: Libellulidae)
(1995) Osborn, Rae.; Samways, Michael John.
Niche and life-history differences in five species of Trithemis were investigated to determine the extent of interspecific competition. Interspecific competition was mostly avoided because species favoured different habitats and microhabitats. There was the possibility of competition between larvae under conditions of lowered food concentration, where they occurred in the same habitat and microhabitat. Larvae of different species preferred specific prey taxa, but chose to feed on a different prey taxon once it was more readily available. Because species were restricted more by food size than taxon, competition for food was unlikely. Interspecific competition may have occurred between adults because the niche breadth of some species became contracted as the density of other species increased. Interspecific competition among larvae was unlikely because individuals of different sizes were present together, allowing for food partitioning. Asynchronous development therefore ensured that competition for food of the same size was reduced. Competition was also reduced by species showing peaks in abundance at different times of the year.

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