Masters Degrees (Entomology)

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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.
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.
Antixenosis and antibiosis as resistance mechanisms of South African sugarcane varieties against early instar larvae of Eldana saccharina Walker (Lepidoptera: Pyralidae)
(2002) Mabulu, Linda Yolanda.; Miller, Raymond Martin.; Keeping, Malcolm G.
The complexity of the behaviour of neonate Eldana saccharina Walker (Lepidoptera: Pyralidae) larvae and the limited information on their response to the morphological characteristics of South African sugarcane varieties was the primary justification to study antixenotic/antibiotic effects on larval behaviour. Laboratory experiments were conducted with stalk segments in plastic jars inoculated with larvae and in a metal cage covered with gauze. In jars, the larvae were observed until they penetrated the stalks. After 14 days, the stalks were dissected and larvae weighed. In all varieties, larvae moved directly to the node after inoculation and penetrated the stalk through leaf scars and buds. No significant differences in larval mass were observed among varieties. In cage experiments different parts of the node, namely the rind below the wax band; the bud; and the root primordia were tested. There was a clear indication that rind hardness and the budscale properties are associated with varietal resistance and only affect early instars. The experiments were repeated using whole cane plants in a glasshouse. The results were similar to those of laboratory experiments. In the Insect Rearing Unit, scraped waxes from different varieties were incorporated into the diet. Larval masses from different diets showed significant differences among varieties, but they did not conform to the known resistance ratings, as cane varieties N12 and N21 showed high susceptibility, instead of resistance. Dispersal behaviour of neonates shortly after hatching was investigated in 'mobility experiments' conducted on live cane plants. Mobility is important because the more time neonates spend wandering around on the stalk surface or on exposed parts of the plant, the more vulnerable they are to predation and other adverse factors that may reduce their survival. Experiments to test stalk penetration by larvae on the node showed that neonates required a softer food source before attacking the hard nodal parts. Second and third instar larvae were used subsequently to the mortality of all neonates fed on the rind, which in turn resulted in non-significant differences, suggesting that feeding on debris and/or leaves is critical to the survival and penetration of larvae into the sugarcane stalk. Incorporation of the characteristics tested in these experiments aims to reduce the number of larvae that penetrate the stalk and to expose them for longer on the surface where their numbers may be controlled by predators and insecticides. The resistant varieties used in these experiments have high fibre and less sugar, but newer varieties, such as N29 and N33 incorporate both high resistance and high sucrose yield, which are the two key elements for optimised sugar production. Chemical characteristics of the plants need to be taken into consideration as high sucrose is seldom found in fibrous varieties. Leaf sheath tightness is another characteristic that would go well with leaf sheath hairiness, because though not tested in this work-would make it difficult for the larvae to get to the smooth adaxial surface of the leaf. The hardness of trichomes is another feature that needs to be investigated, because a variety may have dense, but soft pubescence that does not repel even the most sensitive larvae, neonates. At present, integrating plant resistance with cultural control, i.e. field hygiene etc. is cost-beneficial for the sugar industry.
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.
Aspects influencing the release and establishment of the flowerbud weevil, Anthonomus santacruzi Hustache (Coleoptera : Curculionidae), a biological control agent for Solanum mauritianum scopoli (Solanaceae) in South Africa.
(2011) Hakizimana, Seth.; Olckers, Terence.
Solanum mauritianum (bugweed, woolly nightshade) is a perennial tree native to South America that has invaded many countries including South Africa and New Zealand. In South Africa, after 143 years of naturalization, the plant is ranked as the country‟s sixth worst weed and has invaded 1.76 million ha. Invaded areas include agricultural lands, forest plantations, water courses and conservation areas, especially in the eastern higher rainfall regions. The success of the spread of this weed is due to its production of very high numbers of bird-dispersed seeds. Since conventional control methods are unsustainable in the long term, the weed has been targeted for classical biological control since 1984. Following exploration work in its native range, biological control experts recommended that agents that are able to limit the weed‟s reproductive potential would help to manage the spread and invasiveness of this weed. Anthonomous santacruzi, a flower-feeding weevil found throughout the native range of the weed, was imported and tested between 1998 and 2002. Following approval for its release in South Africa in 2007, a new colony was imported and propagated at the University of KwaZulu-Natal Pietermaritzburg. This study was initiated to investigate aspects that could influence the release and establishment of this agent. Three aspects were investigated namely: (1) reassessing the weevil's host range to confirm that the new colony is not different from the colony tested originally and to assess the risks associated with the release of the weevil in New Zealand; (2) surveying the arthropods associated with S. mauritianum in the field to identify groups of predators that could interfere with the establishment of the weevils as well as to investigate, through laboratory-based trials using spiders as surrogate, the impact of these predators on the survival and proliferation of the weevils; and (3) propagation and release of the weevil and monitoring of its establishment. Host-specificity tests revealed that the host range of new colony is not different from that of the originally tested culture. In no-choice trials, the weevils fed and reproduced on some non-target Solanaceae species but reverted back to S. mauritianum in the choice tests. Although the risks for releasing the weevils in New Zealand were calculated to be very low, additional evidence is needed to demonstrate this conclusively. Future research to provide this evidence includes open-field trials complemented with a chemical ecology study, to resolve the case of two species, a New Zealand native and South African native, which have shown higher risks in comparison to the other tested species. For arthropods associated with S. mauritianum in the field, Araneae (especially Thomisidae), Thysanoptera, Hemiptera (especially Miridae) and Hymenoptera (especially Formicidae) were identified as generalist predators that could interfere with the establishment of A. santacruzi. However, their numbers in the field appear to be too low to provide a major threat. Also, laboratory trials using spiders as a surrogate suggested that A. santacruzi populations can survive and reproduce in the presence of such predators. The weevils were released at four sites in KwaZulu-Natal and monitoring of three of these has confirmed establishment at the warmest site along the South Coast but not at the coldest site in the Midlands. Further releases in the province are intended to complement these promising results, while additional studies are intended to facilitate the weevil's release in New Zealand.
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.
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.
Competition for invertebrate food between the endangered Seychelles Magpie Robin and endemic skinks.
(1998) Le Maitre, Stella.
The endemic landbirds of the Seychelles granitic islands have suffered considerable losses due to predation by introduced rats and cats and extensive habitat destruction. With less than 100 individuals, the Critically Endangered Magpie Robin Copsychus sechellarum Newton, faces the greatest risk of extinction. Translocations to three predator-free islands, Aride, Cousin and Cousine, have provided valuable opportunities for gaining insights into the ecology of the species. Of particular interest are links between the Magpie Robin, endemic skinks Mabvya spp., ground-living invertebrates and seabird colonies. Magpie Robin faecal pellet and skink gut content analysis demonstrated a high degree of dietary overlap between the species. A widespread exotic cockroach Pycnoscelus indicus was the favourite prey item for each species. However, behavioural observations and a dietary choice experiment indicated that there is no significant competition for food during the main seabird breeding season. Invertebrate sampling on Cousine identified 52 species which were available in all habitat types currently in use or those considered suitable for the Magpie Robin. Seabird and skink density counts on Cousine demonstrated the considerable magnitude of vertebrate organic food also available. Invertebrate sampling results on Cousin and Cousine were used to determine territory quality and the carrying capacity of each island for the Magpie Robin. While most seabirds are not breeding, skink survival depends on invertebrate abundance. M. wrightii weight declined throughout this period but that of M. sechellensis remained fairly stable. The data were insufficient to conclude that inter-specific competition for food exists between M. sechellensis and the Magpie Robin during this period. Further expansion of the Magpie Robin population depends on eradicating mammalian predators from other islands and maximising the potential carrying capacities of those already supporting the species.
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.
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.
Ecological aspects and conservation of the invertebrate fauna of the sandstone caves of Table Mountain, Cape Town.
(1998) Sharratt, Norma Joan.
No abstract available.
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.
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.
Epidemiology of human intestinal parasites in Qwa-Qwa, South Africa.
(1995) Mosala, Thabang Innocentia.; Appleton, Christopher Charles.
This study investigated the prevalences and intensity of intestinal parasites and aspects of their epidemiology among children in the Qwa-Qwa region of the eastern Free St~te. Faecal samples of 1180 children differing socio-economic status from nine schools at altitudes varying from 1660m to 2200m were examined quantitatively by means of the formol-ether sedimentation technique. Socio-economic, and demographic characteristics for the communities served by the schools were obtained from the literature and from a questionnaire. The study showed that, the area supports a markedly low diversity of parasite infections, and at lower intensities, than low altitude areas such as the coastal plain of KwaZulu-Natal and Eastern Cape, the Northern Province, Mpumalanga and the Western Cape. The intestinal parasite fauna affecting children in Qwa-Qwa is dominated by protozoans with only few helminths and no hookworm or bilharzia. The results indicated that factors which influence the transmission of intestinal parasites in Qwa-Qwa appear to be related primarily to social, economic and cultural aspects of the peoples' lifestyles. Climatic factors were not found important. There was a significant seasonal effect on the intensities of all parasite infection, except two protozoans, Entamoeba coli and Endolimax nana. Water source, electricity, house-type and quality of meat were found to be the important socio-economic factors that influenced parasite transmission. These relationships were investigated by fitting logistic regression and generalized linear mixed models. By documenting human parasitism (above 1700m) this study provided an endpoint to the altitudinal transect conducted in 1993 in KwaZulu-Natal by Appleton and Gouws (in press). Public health authorities and Primary Health Care personnel should find this study useful when designing and implementing nutrition and parasite control. Severe ascariasis has been reported from the study area. It will help focus PHC activities in Qwa-Qwa and in the wider context of Free State Province by demonstrating the value of proper personal and environmental hygiene in the home, thereby forming the basis for intestinal parasite control at the community level.
Factors affecting millipede, centipede and scorpion diversity in a savanna environment.
(2000) Druce, David James.; Hamer, Michelle Luane.; Slotow, Robert Hugh.
Millipedes, centipedes and scorpions are an important component of the ground-dwelling invertebrate fauna, and may have value as bioindicators of ground-dwelling invertebrate diversity. However, some level of understanding of which factors influence patterns of their distribution and diversity is necessary prior to any investigation of their use in conservation planning and as bioindicators. This project was undertaken in the Greater Makalali Conservancy in the Northern Province. Many methods have been used to sample millipedes, centipedes and scorpions but the efficiency of these in savanna has not been investigated. One aim was to determine a method for quantitatively sampling these invertebrates in this environment. Six sampling methods were tested during the study. Millipedes were found to be efficiently sampled by active searching 9m2 quadrats and drive transects, centipedes by actively searching 25m2 plots and scorpions by pitfall traps. The other methods tested were wet cloths and cryptozoan traps. Another aim was to determine spatial and temporal variation in millipede, centipede and scorpion diversity in the range of habitat types present in the Conservancy. 45 sites within five habitat types were sampled during three different sampling periods. The highest diversity for each study group was recorded in the most heterogeneous habitat, with the lowest being recorded in more homogeneous habitat types. Millipede and centipede diversity was significantly influenced by habitat type, while sampling period had a significant effect on millipede and scorpion diversity. Quantifying the effect of various environmental factors on the diversity of these invertebrates was a further aim. Maps of various Conservancy wide variables as well as micro-habitat variables were created, including an accurate vegetation map, maps of soil characteristics, rainfall and temperature. Micro-habitat characteristics were also recorded within each of the sample sites. Diversity of the three study groups was related to specific micro-habitat variables. A Geographic Information Systems (GIS) model was created, predicting millipede, centipede and scorpion diversity in areas of the Conservancy not sampled. Three undescribed millipede and one centipede species were found and a new distribution record for a scorpion species was documented. These results emphasise the importance of invertebrate biodiversity studies in the savanna environment.
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.
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.
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.
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.

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