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The broad objectives were to better understand the biology of <i>Meloidogyne javanica</i> and to seek cultural and non-chemical control methods of controlling it in tobacco and vegetable rotations in Tanzania. In pot trials <i>Tagetes erecta, Sesame orientale, Arachis hypogea</i> and <i>Zea mays</i> were all shown to be non or poor hosts of <i>M.javanica</i>. These were tested as rotational crops in one or both of two field trials. The core of my work was two rotational trials which extended over three seasons. In the first and third seasons of the field trials susceptible crops (tobacco or tomato) were grown uniformly in all plots. In the second year the various rotational treatments were applied. In both trials <i>Crotolaria ochroleuca</i> greatly reduced <i>M.javanica</i> and increased yields in the third season. The role of root exudates in the effectiveness of <i>T.erecta</i> and <i>C.ochroleuca</i> was studied in pots. Exudate from <i>T. erecta</i> controlled <i>M.javanica</i> on tomato provided it was applied at or before juvenile invasion. That from <i>C.ochroleuca</i> had no effect. In the tomato trial a weedy fallow maintained a substantial population of <i>M.javanica</i> and its weed hosts were examined in a dry season survey of tobacco fields. Two thirds of these which were commonly found were hosts. Solarisation was tried as an additional means of controlling <i>M.javanica</i>. Water bath experiments suggested temperatures above 50<SUP>o</SUP>C were needed for rapid killing of <i>M.javanica</i> eggs. Such soil temperatures were not achieved even under polythene where the maximum was 45<SUP>o</SUP>C. Even so, eggs of <i>M.javanica</i> were killed over 2-3 weeks probably by a combination of temperature and drying. In other temperature studies the base temperature for development of <i>M.javanica</i> was found to be 12.8<SUP>o</SUP>C and thermal constant at 356<SUP>o</SUP>C days. In the continuous tomato plots in the field trial the incidence of <i>M.javanica</i> decreased in the third year associated with a high level of infection with the bacterial parasite <i>Pasturia penetrans</i>. In pot <i>P.penetrans</i> showed promise in reducing infection by <i>M.javanica</i>.

This thesis investigates how host metapopulation processes (local population size and dispersal) affect the prevalence and persistence of ectoparasites of water voles <i>(Arvicola terrestris). </i>Water voles have been found to persist as metapopulations in the study areas in northern Scotland (fragmented populations with frequent extinction and colonisation and linked by dispersal). The ectoparasites examined were: 1) three tick species: <i>Ixodes trianguliceps, Ixodes ricinus </i>and <i>Ixodes apronophorus; </i>2) four flea species: <i>Megabothris walkeri, Peromyscopsylla spectabilis, Ctenopthalmus nobilis </i>and <i>Histrichopsylla talpae; </i>3)<i> </i>two species of mites: <i>Laelaps muris </i>and <i>Hyperlaelaps amphibia. </i>The prevalence and persistence of these parasites were examined over three years in 155 vole sub-populations which varied in density and isolation from each other. The effect of connectivity between vole sub-populations (where the number of immigrants a patch receives can be indexed by both the size of populations in the surrounding area and distance to these populations) on the spatial population dynamics of two tick species: a specialist small mammal tick <i>(I. trianguliceps) </i>and the sheep tick <i>(</i><i>I.</i><i> ricinus) </i>were examined. Connectivity had positive effects on the prevalence and burden of <i>I. trianguliceps </i>but not on <i>I.</i><i> ricinus.</i> The relative effect of local (vole population size/density) versus metapopulation processes (connectivity) on the burden and prevalence of fleas was investigated. Local population dynamics had a weak influence on flea burden and prevalence (no or negative effect) whereas number of infected voles in neighbouring populations increased flea burden and prevalence. Extinction thresholds, taken as connectivity or proportion of habitat loss/“disinfection” below which a parasite cannot persist, were examined and compared for all parasites. Overall, the findings of this study show that host spatial structure and distance dependent dispersal (heterogeneous mixing) are important factors that affect parasite persistence. Therefore, these factors should be considered when planning conservation and disease control programmes.

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The development and pathogenicity of Babesia muratovi and Nippostrongylus brasiliensis were studied in Rowett Hooded rats fed on diets deficient or adequate in copper or in vitamin B12. The course of B. muratovi reached its peak in both adequate and deficient rats on day 6 after infection with inoculum 10⁷/20 g B.W. The parasitaemia was higher and the pathogenicity of Babesia was more severe in rats fed on the copper adequate diets than in copper deficient rats but there was no significant difference between rats fed on vitamin B12 deficient and vitamin B12 supplemented diets. The development of N. brasiliensis in rats was dependent on the dose of larvae inoculated. Higher worm and egg counts were obtained in rats infected with 3,000 larvae than in those infected with 1,500 larvae. The worm and egg counts were higher in simple copper deficient rats and gradually decreased with increasing dietary copper. The egg counts persisted for longer periods in copper deficient rats than in those fed higher levels of copper. The rats inoculated with 3,000 larvae had more severe symptoms. Although in thiomolybdate treated rats the worm and egg counts were lower in deficient than in adequate control rats, the pathogenicity of Nippostronqylus was more severe in deficient rats. The worm and egg counts were highest in vitamin B12 deficient male rats and decreased gradually with increasing dietary vitamin B12, but no such linear trend was seen in females. The development of N. brasiliensis was greater and its pathogenicity was more severe in rats fed diets deficient in copper and vitamin B12 than in those fed on diets adequate in these nutrients.

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