Masters Degrees (Entomology)

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Proximate factors influencing dispersal in the social spider, Stegodyphus mimosarum (Araneae, Eresidae)
(2002) Bodasing, Marilyn Naomi.; Slotow, Robert Hugh.; Crouch, Tanza.
Stegodyphus mimosarum Pavesi,1883 and S. dumicola Pocock, 1898 are two species of philopatric, inbred, permanently communal, non-territorial spiders that co-occur in parts of South Africa. The patchiness of colony distribution, limited dispersal capabilities and the observation of periodic, but rare mass dispersal events raised interest in factors influencing dispersal. The aim of this project was firstly, to determine which factors influence the spiders' readiness to leave a colony (two laboratory experiments), and secondly, to map nest dispersion in Weenen Nature Reserve, Kwa-Zulu Natal, and to use this to explain nest distribution. The first experiment assessed whether group size and variance in access to resources influenced the decision to disperse. Four colony sizes (8, 16,32 and 64) of S. mimosarum were established under a proportional feeding regime. I expected more spiders to leave larger colonies due to intra-group competition. However, there was no significant increase in the number of spiders leaving with increasing group size. Significantly more spiders left a colony during spring and when spiders were large. In the second experiment, I assessed whether the mean amount of food available, in liberally fed or starved colonies influenced the decision to disperse. Five colonies were fed daily on an abundance of prey items and five were starved. I expected more spiders to leave the starved colonies. However, a significant number of spiders left colonies where food was abundant. During a field survey nests were tagged within 40 plots of 50 m radius, and randomly. Retreat dimensions, height above ground, nest position, nearest neighbouring nests, and species were recorded. Nest status was tracked over six months to three years. I confirmed that nest height above ground was significantly higher for S. mimosarum. The two species differed in retreat volume and nearest neighbour distances. Most nests occurred on the northern aspect of trees. Few nests survived beyond three years, although many new nests were established. Access to resources influenced the decision to disperse. However, only well-fed (larger) spiders had the resources to relocate. Patchy nest distribution could be a consequence of nest site selection, short distance dispersal by budding and bridging, and long distance dispersal by ballooning.
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.
Susceptibility and resistance to insecticides among malaria vector mosquitoes in Mozambique.
(2003) Casimiro, Sonia Lina Rodrigues.; Appleton, Christopher Charles.; Sharp, Brian Leslie.
Insecticide resistance in malaria vector mosquitoes reduces the efficacy of insecticide in killing and can therefore cause a major problem for malaria vector control by insecticides. In Mozambique, pyrethroid resistance in Anopheles funestus was first detected in December 1999 in the southern corner of Maputo Province. Since then, various collections have been made at selected sites throughout the country and WHO standard susceptibility tests and biochemical assays were conducted to determine the susceptibility status and the major resistance mechanisms, in the Fl generation of field collected mosquitoes. Three malaria vector species: Anopheles funestus s.s., Anopheles gambiae s.s. and Anopheles arabiensis were identified in this study by Polymerase Chain Reaction (PCR) and their distributions plotted. The susceptibility data indicate that the Anopheles funestus s.s population in southern Mozambique is widely resistant to pyrethroid and with low levels of carbamate resistance evident at six localities. No resistance to organophosphate and DDT was observed at any study sites. Biochemical tests indicate the presence of an altered acetlylcholinesterase in all collection localities with the exception of Massinga district. Elevated esterase activity with substrate a-naphthyl acetate were detect in Boane with a probable role in organophosphate resistance. Elevated GST were detected in Boane, Moamba and Catembe. Very low levels monooxygenase titres were registered in all the localities in Mozambique, which suggest that this resistance mechanism is not operating in these areas. Pyrethroid resistance in the Anopheles gambiae complex was detected only in Anopheles arabiensis from one locality. No resistant to other groups of insecticide were observed. Altered acetlylcholinesterases were registered in all collection localities and in both species: Anopheles gambiae s.s. and Anopheles arabiensis. Elevated esterase with substrate a-naphthyl acetate were detected in Anopheles arabiensis at only one locality. Elevated GSTs were detected at all localities and in both species. The implications of the findings for malaria vector control in Mozambique are discussed.
Phylogenetic systematics of Scrapter (Hymenoptera: Anthophila: Colletidae).
(2006) Davies, Gregory Bernard Peter.; Brothers, Denis John.
Scrapter Lepeletier de Saint-Fargeau & Audinet-Serville, 1828 (Hymenoptera: Aculeatea: Anthophila: Colletidae) is a genus of solitary bees largely endemic to southern Africa. This dissertation investigated the phylogenetic systematics of the genus. Eleven new species of Scrapter are described, principally from the Succulent Karoo biome of South Africa, bringing the total number of species in the genus to 42. An updated dichotomous key to facilitate identification is provided. The previously unknown females of S. albifumus Eardley and S. amplispinatus Eardley are also described. The genus is recorded from outside southern Africa for the first time with the collection of S. nitidus (Friese) in Kenya. This constitutes a significant range extension of the genus. The taxonomic status of five species described by Cockerell in 1944, and subsequently overlooked, is addressed. They are all found to be synonyms of other Scrapter species, except one, which is found to be a Ctenoplectrina species (Apidae: Apinae: Ctenoplectrini). The new synonymies are: S. subincertus Cockerell = S. niger Lepeletier de Saint-Fargeau & Audinet-Serville; S. brunneipennis Cockerell = S. niger Lepeletier de Saint-Fargeau & Audinet-Serville; S. merescens Cockerell = S. leonis Cockerell; S. sinophilus Cockerell = S. algoensis (Friese). Scrapter ugandica Cockerell becomes Ctenoplectrina ugandica (Cockerell) as a new combination. Investigation of selected morphological features (e.g. postmentum, facial fovea, galea) revealed much diversity in Scrapter. The monophyly of Scrapter is not supported by unambiguous apomorphies, but is defensible by the congruence of various qualitative characters (e.g. premental fovea, T2 fovea, hindleg and sternal scopa in [females], two submarginal cells). A cladistic analysis using 25 morphological characters recovered numerous most parsimonious trees under both equal- and successive-weighting. To aid in resolution, several taxa known from only one sex or from very limited material, and with many unknown states, were deleted from the matrix. Analysis using this reduced matrix under equal- and successive-weighting resulted in better resolution, although with low consistency index values. Several subclades were common to both cladograms, and likely represent monophyla. The low consistency indices and general lack of unique synapomorphies upholding these subclades, however, dictated against making any classificatory re-arrangements.
The taxonomy and aspects of the ecology of the Ephemeroidea (Insecta: Ephemeroptera) of the Mooi River, KwaZulu-Natal Province, Republic of South Africa.
(2004) Cahill, Conor.; Hart, Robert Clynton.
The Ephemeroidea or burrowing mayflies are a superfamily of the Ephemeroptera (mayflies) with a worldwide distribution. Recent decades have seen a sharp decline in their abundance globally. Literature reviews of the past 20 years have shown this superfamily to be well represented on the Mooi River, KwaZulu-Natal- five species (Eatonica schoutedeni, Ephemera mooiana, Afromera natalensis, Afroplocia sampsoni and Ephoron savignyi) were recorded during the 20th century. However recent fieldwork failed to confirm this professed diversity, recording only two species (Afromera natalensis and Ephoron savignyi). This work critically re-examined all of the literature relating to the Ephemeroidea of Africa (in the context of the five species recorded from KwaZuluNatal) published in Africa and Europe (as well as many publications from the rest of the world) during the 19th and 20th century. It was found that a number of oversights were made in much of this literature that have become assimilated into the understanding of the taxonomy and ecology of this group. Amongst these, it was found that the synonymisation of three species of Ephoron ( = Polymitarcys-Polymitarcys savignyi, P. capensis and P. temerata) in the 1920s was weakly justified. To clarify problems in the published record relating to the five species recorded from KwaZulu-Natal, some of the most important museum holdings in Europe and South Africa were re-examined. Two previously unknown collections of Ephemera sp. were found in European museums. One of these collections was made in West Africa, undermining theories that Ephemera sp. are only found in cold waters. This research confirmed that the records for Eatonica schoutedeni in KwaZulu-Natal are probably spurious, the result of misidentification. This work presents a review of the publications relating to each of the species of the Ephemeroidea recorded from KwaZulu-Natal. Lists of synonyms are provided. Descriptions from literature and museum specimens are given. The known distribution and biology of each is presented. The current status of the Ephemeroidea of KwaZulu-Natal are discussed and a new key to the species of Kwazulu-Natal is presented. In order to assess the purported diversity of Ephemeroidea in the rivers of the KwaZulu-Natal midlands, extensive fieldwork was carried out the Mooi River and on other tributaries of the Tugela and Mgeni rivers from 1998 to 2000. This investigation failed to reveal four of the five species indicated in the literature. The sole species that was found, Ephoron savignyi was abundant in some areas of the Mooi and Karkloof Rivers. This apparent drop in diversity may be because the sampling effort carried out from 1998 to 2000 was too limited in time and space to gather specimens of all the species resident in the river, or because environmental changes in the region in the last 50 years have resulted in the extirpation of any or all of the remaining four species. It is concluded that the records of Eatonica schoutedeni from KwaZulu-Natal are spurious; Ephemera mooiana is either not the only species in the genus Ephemera on the continent of Africa, or has a substantially wider distribution than previously thought; Afromera natalensis and Afroplocia sampsoni may be present on the rivers of KwaZulu-Natal but have not been found during this research; Ephoron spp. are abundant in KwaZulu-Natal, but further research is required to confirm that the species in South Africa are the same as those originally recorded from the type locality, Egypt.
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.
Population and behavioural studies on Calycomyza eupatorivora spencer (Diptera : Agromyzidae), a biological control agent of Chromolaena odarata (L.) King and Robinson (Asteraceae) in South Africa.
(2011) Nzama, Sindisiwe N.; Olckers, Terence.; Zachariades, Costas.
Chromolaena odorata (L.) King and Robinson (chromolaena, triffid weed) (Asteraceae: Eupatorieae) is one of the most problematic weeds in the subtropical northeastern parts of South Africa. Calycomyza eupatorivora Spencer (Diptera: Agromyzidae) was introduced as a biological control agent for the control of this weed. No study has yet been done to quantify field populations of C. eupatorivora since its establishment in 2003. The aim of this study was therefore to measure aspects of the field population and laboratory behaviour of C. eupatorivora on C. odorata. The first objective was to determine the percentage leaf area mined by larvae of C. eupatorivora on C. odorata plants exposed to three densities of mated flies, and also to determine the number of mines produced by these different densities, and their distribution on the plant. It also attempts to determine the relationship between chromolaena leaf quality and usage by C. eupatorivora. The maximum percentage of leaf area damaged was 37.5% for one of the trials involving five pairs of flies. Mean percentage leaf area damaged was slightly higher with five (28.5%) than ten pairs (22.0%) of adults and was lowest with one pair (6.5%), but these differences were not significant. In relation to the mean number of mines per plant, five and ten pairs of flies caused slightly more mines than one pair. The other significantly different parameter was number of leaves mined per plant, which was higher for five pairs. Within a plant, C. eupatorivora probably selects a subset of leaves with certain chemical and physical characteristics for oviposition since certain leaves were left unmined while others received multiple eggs. Percentage water content did not differ between mined and unmined leaves, but clear patterns were shown by acid detergent lignin which was higher in unmined leaves and nonstructural carbohydrates which were much higher in mined leaves. It is likely that leaf age plays a role in its suitability. The second objective was to quantify C. eupatorivora infestation levels, by counting and examining larval leaf mines, on C. odorata in the field at four times ('seasons' - September, December, March and July) over a 12-month period, and at three study sites that each included two habitats, viz. open and shady. At each of these six sampling sites, line transects were laid out and plants/branches sampled along them. Both plant/branch height and the number of leaves increased between September and March, and plants in the open habitats were taller and had more leaves than those in the shaded habitats. At the third site, the shady habitat supported taller plants with more leaves compared to the same habitat at the other sites. There was a steep increase in the number of C. eupatorivora mines from December to March. The mean number of mines, both total and in relation to leaves available, was highest in March, and was higher in the shaded habitats compared to the open habitats. The mean number of mines per damaged leaf was slightly higher in December compared to the other seasons, and was also higher in the open than the shaded habitats. Mean larval mortality was high (70%) in September but decreased to 32% in December, and increased again in late summer. The overall levels of mining by C. eupatorivora were low, with less than 5% of leaves sampled having mines. Taken together, the laboratory and field trials suggest that C. eupatorivora is restricted to a subset of the leaves of C. odorata for its development; that the field population is unable to make full use of the resource of young, palatable leaves that develop in early- to mid-summer because it only becomes large in late summer; and that the high mortality rate of young larvae negatively affects both the population of the fly and the level of damage to the plant. Given that these results were obtained in an area where the population of C. eupatorivora is relatively high, it is unlikely that the fly is having anything more than a negligible effect on C. odorata in South Africa at present.
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.
Urinary schistosomiasis surveillance in primary health care in South Africa.
(1998) Johnson, Caron.; Appleton, Christopher Charles.
A multifaceted Schistosoma haematobium study aimed at assessing five different diagnostic techniques of surveillance was conducted. Their use in varying operational circumstances with particular reference to Primary Health Care was conducted in three areas of varying prevalence of disease namely; Mpolweni Mission (44.1%), Empangeni (30.3%) and Verulam (72.0%), KwaZulu-Natal, South Africa. This study incorporated both theoretical and applied components. The theoretical components included freshwater snail surveys, review of literature of S. haematobium diagnostic techniques and an assessment of five diagnostic techniques with particular emphasis on diagnostic performance and cost analyses. Added to these components was migration and the assessment of the prevalence of disease amongst occupants of informal settlements in and around the greater Pietermaritzburg city centre. The applied component included the initiation of a holistic S. haematobium control programme based along the World Health Organisation Guidelines. The study provided insight into several of the countries health issues relevant to both schistosomiasis and other diseases and highlighted weaknesses that may hinder the successful implementation of the current National Framework for Parasite Control. The presence of urban schistosomiasis was noted for the first time in the city of Pietermaritzburg. The present schistosomiasis distribution could be influenced by the rural-urban migration that is impacting upon major metropolitan areas. Without intermediate host snail surveys and schistosomiasis prevalence surveys amongst members of the population, the real geographic distribution of the disease will not be known. The diagnostic methods that were compared included sedimentation, filtration, three brands of chemical urinalysis strips, urine colour scales and an indirect questionnaire. Sensitivity, specificity, positive predictive, negative predictive and efficiency values were determined. Using these values, diagnostic performance ranges were established. The ranges were influenced by the cut-off values used, technique and prevalence and intensity of infection of the study area. The chemical urinalysis strips at cut-off 10erythrocyes/μl (73.7% - 93.2%) were highly sensitive whereas urine colour scales (97.1% - 99.4%) and indirect questionnaire (80.4% - 90.3%) were highly specific. The relationship between the community prevalence rates measured by all five techniques varied significantly. A cost-analysis of the techniques/sample demonstrated a wide price range (20c - R4.32). Therefore their use would be dictated more by the availability of funding than by any operational advantages each individual technique may have demonstrated. Within the public health services a need for: (1) staff training programmes, (2) core staff based within the PHC system that is dedicated to parasite control and (3) a strengthening of infrastructure was demonstrated. These may be achieved via workshops, improved communication, education courses, specific time allocation to parasite programmes i.e. parasite week, project co-ordinators and the designation of tasks.
Ecological aspects and conservation of the invertebrate fauna of the sandstone caves of Table Mountain, Cape Town.
(1998) Sharratt, Norma Joan.
No abstract available.
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.
Malaria vector populations associated with the agricultural development at Mamfene, Northern KwaZulu-Natal, South Africa.
(1995) Obala, Andrew Ambogo.; Appleton, Christopher Charles.; Sharp, Brian Leslie.; Le Sueur, David.
The irrigation farming methods on the Makhathini Flats are thought to be responsible for recent increase in malaria cases in the Mamfene area of northern KwaZulu-Natal despite ongoing malaria control activities. Their coincidence with the period of intensive fanning is an interesting one. This study was therefore carried out to determine the relationship between larval habitats and adult mosquito population in malaria transmission using Geographic Information System (GIS). Four types of breeding sites were utilised by malaria vectors in Mamfene, viz; types 1, II, III and IV. Habitat type I was tap pools, type II was irrigation spillage in agricultural land, type III was spillage outside but adjacent to the agricultural land and type IV was depression pools located both in the Balamhlanga swamp and inland. The cumulative larval density in all habitats peaked in March 1995 (20/man-hr), with irrigation spillage (type III) recording the highest density index (33/man-hr) as compared to tap pools (type I) which recorded 32.8/man-hr while other waterbodies recorded I3 .4/man-hr (type II) and O.5/man-hr (type IV) respectively. Subsamples of both larvae and adults of An. gambiae group were identified by the Polymerase Chain Reaction (PCR) technique. Of the larvae identified, 94.1 % and 5.9% (n=289) were An. arabiensis and An. quadriannulatus respectively while in the adult component, the composition was 98.7% and 1.3% (n=303) for An. arabiensis and An. quadriannulatus respectively. This confirmed An. arabiensis as the dominant malaria vector in Mamfene area while the exophilic behaviour of An. quadriannulatus was portrayed. Of the An. gambiae group dissected for parity, 51 .5%) were found parous. This is an indication that the population was old and was able to maintain transmission locally despite ongoing vector control measures. The Global Positioning System (GPS) was used to position larval and adult mosquito sampling sites. The spatial distribution of adult mosquitoes from the breeding sites were plotted using GIS soft ware (Map Info ) and the distance between the breeding sites and study houses were measured using a utility distance tool. With the aid of GIS, the adult mosquito density in houses could be used as an indicator to locate the breeding sites in the vicinity. The importance of these findings in terms of application in cost-effective malaria control cannot be over-emphasized.
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.
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.
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.
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.
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.
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.
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.
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.

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