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The main parasite affecting the Scottish Atlantic salmon farming industry is Lepeophtheirus salmonis costing approximately £29 million annually through lost production and treatments. As such, the primary aim of this study was to investigate the infection pressure, fecundity and infection dynamics of L. salmonis in a west coast sea loch containing salmonid aquaculture. Atlantic salmon held in small sentinel cages were used to monitor sea lice infection pressure in Loch Shieldaig. Investigation of the factors affecting infection pressure within the loch found no evidence of a direct link between monthly gravid lice counts on local farmed salmon and lice burdens on sentinel cage fish. Copepodid L. salmonis were present throughout the year despite there being low numbers of wild salmonids in the system during much of the year and as such the source of this infection was unclear. In subsequent laboratory trials, L. salmonis from wild salmon were found to be more fecund than those from farmed salmon and similarly, fecundity and survival were also higher in summer compared to winter populations of L. salmonis. These findings raise the possibility that L. salmonis infecting wild salmonids may “seed” previously fallowed systems. Alternatively, trials with atypical hosts found that L. salmonis of farmed origin did re-infect Atlantic cod and produce viable egg strings which moulted through to the infective copepodid stage. Infection challenges demonstrated that L. salmonis copepodids were observed to settle on atypical hosts such as saithe and Atlantic cod in low numbers although failed to develop to the chalimus stages and complete its lifecycle. Challenges utilising the mobile pre-adult stage were similarily unsuccesful in allowing L. salmonis to moult to the adult stage on these atypical hosts. Previous work conducted on Pacific three-spined sticklebacks demonstrated the species could support large burdens. In infection trials with three-spined sticklebacks from Scotland’s west coast, settlement was found to be low, which suggests they play no role in the Scottish inshore infection dynamics of L. salmonis. These series of studies provide novel and timely data on the biology and infection dynamics of L. salmonis on typical and atypical hosts in Scottish marine aquaculture areas. The data will form part of the knowledge used to make informed pest management and policy decisions assisting the future development of the aquaculture industry in Scotland.

The Trichinella genus can be broadly divided into two clades that differ in respect to the formation of the host-parasite complex within the muscle cell.  Parasite excretory/secretory (ES) proteins may be responsible for the developmental modification of host cells, as well as the differences observed between the two clades.  Serine proteases are known to be involved in parasite tissue/cell degradation and invasion, and are abundant in the ES protein fraction of mature L1 larvae (ML) of Trichinella spiralis and Trichinella pseudospiralis (representative of the two clades).  Presented here is analysis of the T. spiralis secreted ML serine protease, TspSP-1 and its T. pseudospiralis homologue TppSP-1.  Using the T. spiralis draft genome assembly TspSP-1 was shown to be encoded by a multi-copy gene family, with three genes tandemly repeated.  The putative proteins share high levels of similarity at the N-terminus, which includes the catalytic domain and potentially all encode functional serine proteases.  Comparative analysis of TppSP-1 was carried out and at least one full length cDNA transcript was characterised, though initial results indicated that TppSP-1 may also be encoded by a multi-copy gene family.  Based on TspSP-1, the putative TppSP-1 protein also contained a catalytic domain, though it was lacking one of the catalytic triad residues, indicating a loss of serine protease function.  Several serine protease homologues that have lost catalytic residues have gained other functions, which may also be the case for TppSP-1.  Given the timing of expression is it possible that TspSP-1 and TppSP-1 may be involved in the invasion of the intestinal epithelial cells.  Whether or not these proteins interact with host or parasite proteins and function as typical serine proteases is yet to be determined.

How host and habitat heterogeneity affects the distribution of ticks in the Scottish upland environment was examined, and the prevalence of two important tick-borne diseases in questing, field-collected ticks was investigated.  This data was used to test the predictions of an influential model of louping-ill virus. Both hosts and habitat were found to be important predictors of Ixodes ricinus nymph abundance.  In general, the highest nymph numbers were collected from areas of heather habitat, and lowest numbers from areas of boggy ground.  Nymph numbers increased with increasing red deer density, but were negatively associated with increasing both mountain hare and red grouse density. A total of 1063 field collected, questing ticks were individually tested for louping-ill virus, of which 621 were also tested for Borrelia burgdorferi sensu lato.  Louping-ill RNA was detected in 7.8 % of all ticks tested.  The percentage of ticks positive for louping-ill virus did not vary with tick stage, collection site, month, or vegetation type, and was not correlated with host density of host seroprevalence.  B. burgdorferi was detected in 1.4 % of the ticks.  No simultaneous infections of louping ill virus and Borrelia spp. were detected. Field data on tick abundance and pathogen prevalence collected during this study was used to challenge an influential model of louping-ill virus dynamics.  The model proved relatively successful at predicting tick abundance, but underestimated the extent of louping-ill virus.  The single patch model was adapted to form a two-patch modelling allowing red deer movement between the two patches.  Allowing the movement of deer between two patches with different host densities shifted the threshold for louping-ill virus persistence, allowing its persistence in almost all red deer-grouse-hare scenarios.

This thesis investigates how host metapopulation processes (local population size and dispersal) affect the prevalence and persistence of ectoparasites of water voles (Arvicola terrestris). 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: Ixodes trianguliceps, Ixodes ricinus and Ixodes apronophorus; 2) four flea species: Megabothris walkeri, Peromyscopsylla spectabilis, Ctenopthalmus nobilis and Histrichopsylla talpae; 3) two species of mites: Laelaps muris and Hyperlaelaps amphibia. 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. trianguliceps) and the sheep tick (I. ricinus) were examined. Connectivity had positive effects on the prevalence and burden of I. trianguliceps but not on I. ricinus. 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.

The aim of the study was to investigate the role of helminth parasites in the population ecology of the wood mouse Apodemus sylvaticus in the field. Specifically, the study determined the species richness, prevalence and intensity of helminths in wood mice in deciduous woodland at Balmedie, Aberdeenshire, North East Scotland and evaluated faecal egg counting technique for detecting and estimating worm burdens of helminths in wood mice. In a capture-mark-recapture field experiment both the prevalence and intensity of helminths were manipulated by administering the anthelmintics Levamisole and Praziquantel to wood mice in deciduous woodland (Foveran and Auchmacoy, Aberdeenshire). Wood mice captured in Balmedie woodland harboured 3 species of nematode, Heligmosomoides polygyrus, Syphacia stroma and Trichuris muris, the digenean Brachylaemus recurvum and 2 species of cestode Skrjabinotaenia labota and a larval strobilocercus of Taenia taeniaeformis. Frequency distributions of all helminths other than T. muris and T. taeniaeformis, displayed over-dispersion. The prevalence and intensity of infection of the helminths showed a clear pattern of seasonal variation. There were no significant differences in the prevalence and intensity of infection of helminths between male and female wood mice. The intensity of infection of H. polygyrus and S. stroma was higher in heavier (older) mice. Wood mice underwent seasonal variation in density at both Foveran and Auchmacoy woodlands. The density of mice was greatest in late autumn/early winter and declined through the spring, being lowest in late spring / early summer. The density increased throughout summer and was highest in later summer / early autumn at Auchmacoy and in early winter at Foveran. At each site, the population density was similar in control and heated grids. Adult male and female wood mice showed a clear pattern of seasonal variation in mean body weight at both study sites. The mean body weights were highest in summer, declined through autumn being lowest in late autumn and early winter. There were no significant seasonal (breeding vs non-breeding) and treatment (control vs treatment) effects on the mean body weights of adult male and female wood mice.

This thesis examined the physiological, behavioural and pathological effects of sea lice, Lepeophtheirus salmonis (Krøyer, 1837), on wild sea trout, Salmo trutta L., and experimentally infected sea trout and Atlantic salmon, Salmo salar L. to determine how, and to what extent, sea lice cause mortality of their infected hosts. A feeding hierarchy was established in groups of sea lice infected and uninfected Atlantic salmon as a physiological stressor. Results indicated that chalimus did not stimulate physiological changes leading to marine mortality and the intensity of the sea lice infection on a fish was independent of that individual's food consumption. However, preadult stages caused appetite suppression, severe skin lesions and changes in the blood biochemistry of the fish with subsequent recovery to the levels of uninfected fish as the parasite moulted through to the adult stages of the lifecycle. The effects of sea lice on sea trout at either 2 or 6 weeks after sea water transfer were assessed. Both infection intensity and developmental rate were not significantly different between the groups, but a trend of fewer lice on the fish infected 6 weeks after sea water transfer was recorded. Fewer of the fish infected 2 weeks after sea water transfer had resumed feeding by the end of the experiment, leading to a loss of body condition, and suffered more severe damage to the skin and detrimental changes in the physiological integrity as a consequence of feeding preadult lice. The mortal impact of sea lice infection was significantly enhanced in the fish infected 2 weeks after sea water transfer. The findings from this thesis have shown that preadult sea lice can cause mortality of wild and experimentally infected sea trout and Atlantic salmon, particularly if infected at the time of sea water transfer, but under certain conditions sea lice infected hosts can recover from the detrimental effects of both chalimus and mobile stages.

Infestation of commercially reared salmonids with the salmon louse Lepeophtheirus salmonis, is a large problem for the fish farming industries in Scotland, Ireland and Norway. Lice infestations cause high fish mortalities and losses in revenue for the fish farmer. Conventional treatment of lice infestation involves the use of organophosphate insecticides which are limited in their efficacy against lice, as well as being highly toxic to the flora and fauna which surround the sea cages. We have investigated the possibility of producing a recombinant vaccine against L. salmonis based on immunisation of farmed salmonids with 'concealed' antigens from lice. Murine monoclonal antibodies were raised against L. salmonis antigens using standard cell fusion techniques. The antibodies were screened by immunohistochemistry in order to establish the location of the recognised antigen in L. salmonis sections. We used the monoclonal antibodies to screen L. salmonis DNA libraries constructed in gt11 and ZAP in order to isolate the DNA coding for each recognised antigen. A monoclonal antibody was produced which showed strong immunoreactivity with cuticle-associated areas in lice sections. This antibody was subsequently shown to recognise the enzyme chitinase from L. salmonis. We have expressed recombinant proteins from the isolated phage which have been used in immunisation trials on the Atlantic salmon (Salmo salar). Lice feeding on fish immunised with three of the recombinant antigens, displayed abnormal egg development and an overall decrease in egg number. We are currently retesting these antigens in a larger immunisation trial. We have also used polymerase chain reaction technology to look for known genes in L. salmonis and have identified a member of the wnt gene family, wnt-5a.

The broad objectives were to better understand the biology of Meloidogyne javanica and to seek cultural and non-chemical control methods of controlling it in tobacco and vegetable rotations in Tanzania. In pot trials Tagetes erecta, Sesame orientale, Arachis hypogea and Zea mays were all shown to be non or poor hosts of M.javanica. 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 Crotolaria ochroleuca greatly reduced M.javanica and increased yields in the third season. The role of root exudates in the effectiveness of T.erecta and C.ochroleuca was studied in pots. Exudate from T. erecta controlled M.javanica on tomato provided it was applied at or before juvenile invasion. That from C.ochroleuca had no effect. In the tomato trial a weedy fallow maintained a substantial population of M.javanica 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 M.javanica. Water bath experiments suggested temperatures above 50^oC were needed for rapid killing of M.javanica eggs. Such soil temperatures were not achieved even under polythene where the maximum was 45^oC. Even so, eggs of M.javanica were killed over 2-3 weeks probably by a combination of temperature and drying. In other temperature studies the base temperature for development of M.javanica was found to be 12.8^oC and thermal constant at 356^oC days. In the continuous tomato plots in the field trial the incidence of M.javanica decreased in the third year associated with a high level of infection with the bacterial parasite Pasturia penetrans. In pot P.penetrans showed promise in reducing infection by M.javanica.

Diphyllobothrium dendriticum and D. ditremum have a wide distribution in the trout of Scottish lochs, although no specific trends in their overall distribution have been observed. The seasonal recruitment trends and development of infections with Diphyllobothrium spp. pleroceroids in wild rainbow trout, in one particular Scottish loch, were monitored regularly for the period 1986 to 1989. Infection varied between these years, but in 1987 intensities from March to November reached their highest levels in November when sampling ended. These two species reached infection intensities, in individual fish, higher than any previous reports and trout stocks appeared to be affected. Plerocercoids, in host-derived cysts, were located on the peritoneal stomach surface, the gross pathology of which is described. The cellular components of the host-derived cyst were examined in detail by light and electron microscopy. A number of leucocyte types, found within a collagenous matrix with associated fibroblasts, were observed. Leucocyte types included neutrophils, eosinophilic granular leucocytes, macrophages and occasional plasma cells. Antibody production, in response to natural infection, was examined by indirect immunofluorescence using serum on cryostat sections of plerocercoids obtained from wild-caught rainbow trout. The tegument of these larvae showed a positive fluorescence, indicating the presence of serum antibody in these trout. Semi-quantitative estimates of antibody titres were estimated by an optimised enzyme-linked immunosorbent assay (ELISA). To facilitate further examination of the events associated with the establishment of plerocercoids and associated host-derived cyst, under controlled conditions, a routinely maintained laboratory life cycle of D. dendriticum was established. This laboratory life cycle utilised Herring gulls (Larus agentatus) and the copepod, Cyclops abyssorum, as the definitive and first intermediate hosts respectively, and provided plerocercoid infections in trout which were examined at various times post infection. Tegumental extracts from the plerocercoids of D. dendriticum, obtained by freezing and thawing specimens, and conditioned medium obtained after in vitro maintenance of live plerocercoids, were prepared. These extracts were tested in respiratory burst assays and were found to stimulate the production of both hydrogen peroxide and superoxide anion by rainbow trout macrophages. The migratory responses of trout macrophages and neutrophils to these agents were also investigated, by an optimised Boyden technique using a 48 Well Micro Chemotaxis Chamber. Leucocytes were found to have an increased chemokinetic motility following stimulation/contact with these antigen preparations. Finally, to investigate if antigens on live parasites were attractive/stimulatory, an in vitro adherence assay was carried out. Procercoid stages, which share common antigens with the plerocercoid stage, were maintained in vitro and incubated with rainbow trout leucocyte suspensions, in the absence and presence of normal or immune serum from infected fish. Leucocytes adherence was considerably increased by the presence of immune serum, indicating the possible interaction of the non-specific and specific immune response in the host inflammatory reaction.

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.

Loch of Strathbeg is a coastal dune lake, about 40 miles north of Aberdeen. The loch is fed by one burn, Burn of Savoch. The River Don tributaries are about 35 miles west of Aberdeen. The main groups of aquatic invertebrates include Hirudinea, Oligochaete, Crustacea, Coleoptera, Diptera, Hemiptera, Ephemeroptera and Mollusca. The terrestrial forms are mainly Coleoptera, Hymenoptera, Diptera and Hemiptera. The loch is also rich in avifauna especially in autumn and winter. Fish species include trout, sticklebacks, flounders and eels. The Don tributaries are comparatively poor in species of inverte-brates. Most insects belong to two orders, Ephemeroptera and ple-coptera. In addition, there are numerous freshwater shrimps, Gammarus pulex, which form one of the major food items of trout and other fish in the area. The piscifauna of the area include trout, salmon, eels, brook lamprey and sticklebacks. Strathbeg trout do not live for more than 4+ years. Growth of trout in Loch of Strathbeg, Burn of Savoch and Don tri-butaries has been calculated. Loch fish grow more than double their length when they enter the loch in their second year (1+) during this year. In the other two habitats, growth is more gradual. This is dearly demonstrated by their specific growth rates (Fig 4 p.23.). The average length of fish at different ages are equal for both Burn of Savoch and Don fish but almost half the size of their loch counterparts. Growth of trout 'at Strathbeg and Don has been suggested to be influenced mainly by the food, temperature and the availability of spawning facilities. The Don area has good spawning grounds and therefore supports more populations of trout which ultimately results in the decrease in the growth rate due to competition for food and space. This even-tually leads to fast growth of fish due to lower competition for food and space. Trout are surface feeders between May and October, and bottom feeders between November and April. Surface food is predominantly of terrestrial origin and emerging insects, while bottom food is both of permanent e.g. molluscs and shrimps, or temporary bottom origin e.g. insect larvae. Terrestrial food is either washed into the water by waves or blown into the water by wind or is captured when flying over the loch (see Table 6). The main food In the loch includes Diptera larvae, pupae and adults, Hemiptera (mainly corixids), Ephemeroptera (mainly Cloeon simile), Coleoptora (mainly terrestrial beetles) and Trichoptera. Molluscs (mainly P jenkinsi) form about 2.8% of the total food consumed by trout in the loch. sticklebacks form an important dietary item of larger trout. A total of 18 helminth species and one molluscan parasite were recorded in Strathbeg and Don trout, with 14 species, including glochidia larvae, in the former and 12 in the latter. Two species of crepidostomum, C metoecus and C farionis, were recovered from the two habitats studied. Attempts have been made to separate the two species. C. metoecus is a parasite mainly of the pyloric caeca while C farionis is mainly a parasite of the intestine and the gall bladder. C metoecus is more abundant than C. farionis. A clear seasonality has been recorded for C. metoecus. Mature worms disappear in July/August and juveniles appear at the same time. Three additional intermediate hosts of Crepidostomum have been recorded. These are Cloron simile, Siphlonurus lacustris and Bphemerella ignita. Two species of diplostomuli have been observed in the lens and humour of trout. Infection of trout at Strathbeg with both meta-cercariae takes place in the loch. Infection of trout with humour specimens is significantly higher than that of the lens specimens in both Strathbeg and Don fish. Infection with both species of parasites increases with the age of fish. Infection increases with the age of fish from 1+ to 4+. Younger fish (0+) are not infected by these tapeworms. It is concluded that intermediate hosts and their consumption by trout are the major factors affecting the intensity of infection of these fish. It is added that when considering the parasite fauna of a stocked body of water, the history of the fish and the habitat before stocking should be taken into consideration, Factors that affect parasite transmission to trout include availability of hosts, temperature of the environment, feeding behaviour of trout and movement of trout to and from infected areas. From the result of this work, infection of Strathbeg trout with both Diphyllobothrium and Eustrongylides is to a large extent responsible for the total disappearance of fish older than 4+ in the loch.

The reasons for the declines in red grouse numbers that occur periodically on the heather moors in the British Isles, have been uncertain for a long time. During some declines many grouse are found dead in poor condition, bearing thousands of tiny threadworms Trichostrongylus tenuis in their intestinal caeca. The purpose of my study has been to find whether threadworms alter the health of well-fed grouse. Although 90% of wild grouse that I examined carried threadworms, old birds had 30 times as many as young birds, and most of the worm population was carried by a few heavily infected grouse. This highly skewed distribution of parasites within hosts is common in parasite infections. Grouse become infected with threadworms when they eat worm larvae on heather. During the present study, adult worms were well tolerated by grouse and produced eggs which were passed in the birds' faeces for over a year. Nevertheless, the immune system of the birds seemed to be reacting to the presence of either larvae or worms, in that the numbers of circulating eosinophils and heterophils rose as did the concentration of alpha, beta and gamma globulin. The pathogenic effects of worms varied amongst individual grouse, and some grouse carrying 3000 - 4000 worms died while others survived with many times more. Infected grouse developed a mild anaemia and the levels of serum albumin in their blood fell. Body weight did not change but muscle masses shrank. These physiological changes were associated with a reduction in dominance of captive grouse at least in the short term, although two wild grouse dosed with trichostrongyles maintained their territories and breeding status. The idea of a link between trichostrongyles and either the dominance of grouse or their ability to hold territories should be retested. In conclusion, trichostrongyles reduce the condition of grouse and other physiological variables usually associated with good health, although they do not kill many well-fed grouse. In the wild, these effects might contribute to declines in population, especially if associated with poor nutrition.

The maintenance of adult schistosomes in vitro is characterised by transient production of eggs, limited survival and a visible deterioration in worms during prolonged maintenance. Empirical, or trial and error attempts at improving media for the in vitro maintenance of adult S. mansoni have proved largely unsuccessful. The present study employed a more logical, biochemical approach to in vitro maintenance by quantifying the deleterious changes occurring in. vitro, in an attempt to identify the causes of the rapid cessation of egg production and the concomitant worm deterioration. C2) In Medium 199 supplemented with 10% newborn calf serum, adult mansoni produced a total of 400 eggs per pair during the first 10 days in vitro. Egg deposition was rarely observed beyond this period even though worms survived for up to 60 days. (3) There was a decrease in schistosome biomass during maintenance in vitro. Over 10 days the dry weight of males decreased by 30% while the dry weight of females fell to 50% of its level at isolation from the host. C4) During 5 days vitro the protein content of male schistosomes fell by 30%. There was a corresponding decrease in the protein content of females of 60%. The loss of schistosome gut contents in vitro would account for some but not all of this decline. (5) At least 50% of the glycogen of male S. mansoni was depleted during the first 6 h in vitro. Female glycogen content was less affected by vitro maintenance. The glycogen content of both male and female worms decreased during prolonged in vitro maintenance. The level of glycogen depletion during the initial 24 h in vitro was apparently unaffected by the glucose concentration in the incubation medium. (6) Studies of the uptake and incorporation of glucose, adenine, and the amino acids leucine and alanine from the incubation medium were used to examine the metabolic differences between worms incubated as pairs and worms incubated following separation. (7) Male S. mansoni were capable of fulfilling their biosynthetic amino acid and adenine requirements in copula through trans-integumental uptake whereas paired females were not. (8) Allowing for the obscuring of the tegumental surfaces in copula and for the loss of gut contents, the amino acid uptake and incorporation rates of male and female S. mansoni in vitro reflected the changing somatic requirements of the worms. (9) Amino acid uptake rate and the rate of incorporation of amino acids into schistosome protein were not related to reproductive activity in vitro. CIO) The rates of uptake and incorporation of adenine also reflected somatic rather than germinal requirements, and were not related to reproductive activity in vitro. (11) Adult paired S. mansoni removed the equivalent of twice their combined body dry weight of glucose from the medium during each day of the initial 3 days in vitro. (12) The rapid depletion of male glycogen in vitro appeared to be caused by a decrease in the rate of incorporation of glucose into glycogen by the male worms during the first hour jin vitro. A concomitant decrease was not observed in female schistosomes. (13) Increases in both the rate of uptake of glucose and the rate of its incorporation into glycogen were effected by increasing the glucose concentration in the medium and by the incubation of separated male and female worms. (14) It is proposed that the cessation of egg production and the observed decrease in worm biomass in vitro are due to the failure of adult schistosomes to feed on red blood cells in vitro and that the rates of uptake and incorporation of metabolic precursors in vitro merely reflect the decreasing worm biomass and have little significance to reproductive function in vitro.