No description available.

No description available.

No description available.

No description available.

The studies within this thesis have made a valuable contribution to our understanding of anthelmintic resistance in Scotland and in particular to the prevalence of benzimidazole (BZ) and ivermectin (IVM) resistance, the expression of multiple resistance and its management. Parasitic gastroenteritis (PGE) is a major welfare issue not only for Scottish, UK and European farmers but also for livestock producers throughout the world. Parasites such as Haemonchus, Trichostrongylus and Teladorsagia are estimated to cost the sheep industry hundreds of millions of dollars annually. To date control has largely been achieved using anthelmintics, but over reliance on anthelmintics has led to the development of multi class anthelmintic resistance (AR) and the realization that intensive chemoprophylaxis is not a sustainable approach for the control of nematodoses. The first two papers contributing to this thesis assessed the prevalence of benzimidazole (BZ) and ivermectin (IVM) resistance within ovine gastrointestinal nematode populations in Scotland. The prevalence of BZ resistance in selected Scottish lowland sheep farms was around 24% in 1991 but this had risen to over 80% by 2001. The first cases of ivermectin resistance in sheep were only detected in 2001 but a small scale survey in 2004 showed that 35% of the farms (6 from 17) surveyed had IVM resistance, with Teladorsagia and Trichostrongylus being identified as the resistant genera. The isolation of a triple class resistant T. circumcincta (MTci5) population has enabled research to focus on the important issue of the therapeutic and prophylactic management of this emerging problem. The third and fourth papers detail a series of controlled efficacy tests conducted on MTci5 that confirmed, in the short term at least, it should be possible to use a milbemycin (moxidectin; MOX) or combination treatments, with IVM and one other class of anthelmintic to control nematodoses (>90% efficacy) caused by adult and/or immature worms. However the study examining larval susceptibility highlighted the important role that immature stages can play in the selection and transmission of resistance. Currently there are no tests that can detect the presence of these resistant larval stages. The fifth paper outlines parasitological findings from the farm where MTci5 was isolated following the confirmation of multiple class resistance. Substantial efforts were made to find solutions to maintain sustainability and profitability of the enterprise though ultimately the use of MOX selected for a, predominately Teladorsagia, population against which the persistent activity of the compound was only negligible with the reappearance of eggs in faeces occurring between 21 and 28 days post treatment. Effective sustainable control of AR populations not only requires an understanding of the phenotypic and genotypic mechanisms that underpin resistance but also improved means of ensuring that our farmers are made aware of and utilize identified best practice approaches. The written and verbal responses of the farmers to questions relating to best practice advice (papers six and seven) would suggest that many of the recommendations for delaying the selection and transmission of AR (ACME, Moredun Foundation and sustainable control of parasites of sheep (SCOPS), DEFRA) are not being followed, recommendations such as the effective quarantine treatment of newly purchased animals and dosing animals at the manufacturers’ recommended dose rate were followed by only 20% and 56% of farmers respectively.

Root-knot nematodes (RKN) are plant parasites, and a major agricultural pest. RKN are adept at invading and feeding on plant tissue with secretions they release from their gland cells. This thesis compares glandular development in Meloidogyne to the model nematode, Caenorhabditis elegans. Pharyngeal and gland important transcription factors, PHA-4 and HLH-6, respectively, were examined for their role in regulation of parasite-specific genes. Homologues of these genes were identified and sequenced from M. incognita. Phylogenetic analyses revealed a new PPN-specific gene, hlh-6-like. Bioinformatic comparisons of the homologues revealed conservation of the DNA-binding motifs of Ce-HLH-6 and Mi-HLH-6 proteins, as well as conservation of their promoter regions. While HLH-6 antibodies proved inconclusive, expression assays revealed expectant levels of PHA-4 and HLH-6 in Meloidogyne as compared to C. elegans. In identifying genes essential for parasitism we are providing new targets for knockdown during RKN infection. / October 2016

The prevailing use of chemical pesticides has generated several problems including insecticide resistance, outbreak of secondary pests, safety risks for humans and domestic animals, contamination of ground water and decrease in biodiversity among other environmental concerns (Webster, 1982). These problems and the nonsustainability of control programs based mainly on conventional insecticides have stimulated increased interest in the development and implementation of costeffective, environmentally safe alternatives to chemical pesticides for insect pest control. One of the most promising strategies to help minimize dependence on chemical pesticides has been the recent application of entomopathogenic nematodes (EPNs) as biocontrol agents. EPNs in the families Steinernematidae and Heterorhabdidae have been shown to have considerable potential as biological control agents. As a natural process, biological control has the potential to play an important role in the suppression of field crop pests in agriculture. EPNs as biocontrol agents have the following advantages: high virulence, safety to non target organisms, ability to search for hosts, high efficacy in favourable habitats, high reproductive potential, ease of mass production, ease of application (Ferron & Deguine, 1996). To isolate the EPNs in South African soil, 200 soil samples were randomly collected from 5 locations in the agricultural research council (ARC) Pretoria, Gauteng province in April 2006; and 5 locations in Brits, North West province in March, 2006. At the different collection sites, soil samples were obtained from soils associated with various types of vegetation. The nematodes were collected from sandy soil by the insect-baiting technique and maintained successfully in vivo for 12 months on Galleria mellonella (G. mellonella), 4 months on Tenebrio molitor (T.molitor); 2 months Pupae and in vitro (lipid agar) for 2 weeks in the laboratory. Out of a total of 200 soil samples that were baited, 2 were found to be positive for EPNs.EPNs. IV In addition to completing Koch’s postulates, the colour of cadavers infected by the putative EPNs were also used as a diagnostic characteristic for categorizing the nematode isolates. Characterization and identification of the EPN isolates were based on morphological characters, as well as on a molecular marker (18S rDNA). On the basis of the morphological and molecular data that was obtained both of the EPNs isolates were placed in the family Heterorhabdidae: Heterorhabditis bacteriophora (H. bacteriophora) and Heterorhabditis zealandica (H. zealandica). Also from the phylogenetic trees generated from the 18S rDNA sequence, the indigenous putative H. bacteriophora was shown to be closely related to H. bacteriophora (accession number EF690469) and indigenous putative H. zealandica to H. zealandica (accession number AY321481). The two EPNs were found associated with Gram negative rod-shaped bacteria. The bacterial symbionts of the two isolates were isolated and a region of the 16S rDNA gene was sequenced. National Center for Biotechnology Information (NCBI-BLAST) results of the 16S rDNA sequence obtained showed the endosybiotic bacteria to be Photorhabdus luminescens laumondii (P. laumondii) (H. bacteriophora) and Photorhabdus sp (H. zealandica). Results of the tree showed that isolates from H. bacteriophora appeared to be closely related to P. luminescens subsp laumondii strain TT01 Ay 278646. The isolates from H. zealandica appeared to be most closely related to Photorhabdus sp Accession number: Q 614 Ay 216500). Bioassays were used to determine the infectivity of the two EPNs. In this experiment different infective juvenile (IJs) concentrations (5, 10, 25, 50, 100,200 400 and 500) of the two EPNs were applied per G. mellonella; T. molitor larva and pupae. The bioassay was carried out in two parts. In the first part, mortality data was collected for H. bacteriophora and H. zealandica. The results showed that the degree of susceptibility of G. mellonella, T. molitor larvae and pupae to each nematode species was different. When 24 h post-exposure mortality data for larvae exposed to the IJs of H. bacteriophora and H. zealandica were analyzed, ANOVA showed no differences V in mortality between insects exposed to different H. bacteriophora IJ doses (Fig: 8.1 ABC). However, there were significant differences in mortality between insects exposed to different IJ doses of H. zealandica such as 5 and 500 IJs/insect (Fig: 8.2 ABC) Therefore, no differences were noted when mortality data was compared between IJ doses at both 72 h and 96 h following IJ application to the insects. The highest susceptibility was observed with G. mellonella followed by T. molitor pupae and then T. molitor larvae. According to Caroli et al., (1996), the total mortality of insect such as G. mellonella and other lepidopterans, was reached within 24-72 h of exposure to nematodes at concentrations such as those tested here. In this study similar results were observed with high concentration of nematodes (100, 200 and 500). In the second part of the dose response bioassay, the number of progeny IJs emerging from EPN-infected cadavers was determined for all two EPNs. The results indicate that IJ progeny production differed among the three insect hosts used, the IJ doses they were exposed to, as well as the EPN species (Figs 8.3 & 8.4). The highest number of emerged IJs of H. zealandica was produced by G. mellonella (mean ± SEM: 220500 ± 133933 IJs), followed by T. molitor larvae (mean ± SEM: 152133 ± 45466 IJs) and the lowest then T. molitor pupae (mean ± SEM: 103366 ± 56933 IJs).

Parasites are important drivers of ecological and evolutionary processes in their hosts. However, hosts often differ in how they are affected by parasitism, which can be important in how parasite effects on individuals scale up to the population level. Hosts may differ intrinsically in their susceptibility to parasitism, and extrinsic factors may impose constraints on how hosts allocate resources between immunity, maintenance and reproduction, thereby further affecting their ability to cope with infection. These extrinsic factors include the host’s ecological environment, for example food availability or weather, and its social environment, that is its interactions with conspecifics. This is particularly true during a reproductive attempt when individuals interact closely with other family members. Not only might immediate impacts of parasitism differ between and within parents and offspring, but the direct effects of parasitism on a host could have further indirect consequences for other family members through their behavioural interactions with parasitised individuals. The distribution of direct and indirect effects among all family members could affect the outcome of the breeding event and individuals’ future performance. However, teasing apart these various avenues of parasite impacts on families may be difficult if parasite burden or susceptibility is correlated between family members. In this thesis, I explore the consequences of parasitism for different family members of the European shag Phalacrocorax aristotelis infected with gastrointestinal nematodes, over a range of ecological conditions. In chapter 2, I demonstrate that chicks’ responses to anti-parasite treatment across four years vary between siblings and with environmental conditions, which may be mediated by resource allocation among siblings. In chapter 3, I explore how costs of parasitism are distributed among the whole family by simultaneously treating chicks and/or parents with an anti-parasite drug and measuring the outcomes for all family members. Treatment has a more marked effect for the non-treated generation than for the treated individuals, suggesting that parasitism may have important indirect costs. In chapter 4, I investigate whether within-brood variability in the effects of anti-parasite treatment and its cross-generational impacts are mediated by behavioural change, and show that chick treatment but not parent treatment influences several aspects of behaviour in the nest. In chapter 5, I demonstrate that the impact of chick anti-parasite treatment on parents persists beyond the breeding attempt, with parents of treated chicks foraging less overwinter and breeding earlier the following year, whereas there is no persistent effect of parents’ own anti-parasite treatment. Lastly, I provide an appendix examining the parasitology of the system in detail, including an assessment of in situ and proxy measures of worm burdens of chicks. This thesis demonstrates that parasitism can be a key component, previously overlooked, of reproductive performance in seabirds, a group that plays an important ecological role as apex predators and thus indicator species of the marine environment.

Thesis (M. Sc. (Biochemistry)) -- University of Limpopo, 2003 / Refer to document / National Research Foundation (NRF)

Plant nematodes belong to a large group of invertebrates known as round worms, They derive their name from the Greek word "nema," meaning thread. In literature some authors refer to nematodes as nemas. In England and many parts of the United States, plant-parasitic nematodes are called eelworms. While some damage to plants results from mechanical injury, salivary secretions injected by the nematode into the plant are usually the major cause of damage. Experiments conducted in the first part of the present century have demonstrated large differences in plant growth in soil infested with nematodes and soil freed of nematodes by chemicals. Any plant subjected to nematode attack is reduced in growth. The most important nematode which attacks and retards the growth of alfalfa in Utah is the stem nematode. This parasite has been reported in most of the major alfalfa-producing counties of the state. In certain areas the nematode is prevalent to such a degree that only resistant varieties can be grown if the crop is to remain for more than two or three years. In other areas stands and yields are reduced in varying degrees. In many additional areas it is not known if the stem nematode is present, since a complete survey of the state has never been made. The objectives of this investigation were to determine the distribution of the stem nematode of alfalfa through a complete survey of the state. The physical factors of the plant and soil which may be correlated with the presence of the nematode were likewise surveyed.