No description available.

No description available.

No description available.

Larval mortality of the face fly, Musca autumnalis De Geer, due to the biotic environment in Virginia was determined to be approximately 62.7% during the sumer of 1967 in preliminary studies. This was based on the difference in numbers of pupae resulting from an insect~accessible tray and an insect~proof tray, Each was filled with bovine manure and both contained approximately equal numbers of eggs or new first—instar larvae when placed in the field, Pupae of the major species of coprophagous Diptera resulting from pasture droppings of bovine feces were collected in sandboxes and furnels from three areas of Montgomery County, Virginie during 1967. The pupae were separated according to species, incubated, and examined afterwards to determine the fate of each pupas, Special emphasis was placed on the parasites involved and the portion of total porasitization contributed by each species, Primary interest was in biological reculation of face fly populations, Other flies were studied for comparison and to determine natural reservoirs of parasites, Comparisons of data from sandboxes with those from funnels showed a higher over-all rate of parasitism in the sandboxes than in the funnels. Other techniques for attempting to obtain new parasites of the face fly were also employed, Adult face flies were examined for nematodes, Heterotylenchus autumnalis Nickle. Approximately 16% of the natural population were infested during 1966-7. Available data for mortality during different life stages were combined into a preliminary life table for the face fly. Muscidifurax raptor Girault and Sanders, a pteromalid parasite, was recovered in low numbers from face fly pupae during 1966 field studies, It has been successfully propagated in the laboratory on face fly pupae by mechanically cracking the fly puparia to aid emergence of the parasites, Parasitism is normally accomplished by penetration of the ovipositor throush the posterior spiracles of the host, The ovipositor of one female was observed to penetrate the anterior spiracle of a face fly pupa. Muscidifurax ravtor is not limited to the spiracles for penetration of house fly pupae. Muscidifurex raptor was found on several hosts in nature. Eucoila sp., Xyalophora quinouelineata (Say), Aleochora tristis Gravenhorst, and A. bimaculata Gravenhorst, which are parasites of coprophagous Diptera, were hyperparasitized by M. raptor. Studies on the biology and behavlor of M. raptor were conducted in the laboratoiy, Its effectiveness in parisitizing different hosts was compared on house fly and face Fly pupae. / Ph. D.

The objectives were (1) to survey the helminthfauna of the beaver, <i>Castor canadensis</i>, collected in western Maryland, particularly Garrett County, (2) to relate the helminth infections to sex, age, weight, and general condition of the beaver, and (3) to record any evidence of gross pathology involving helminths. A sample of 63 beaver, 31 males and 32 females, was obtained from Garrett, Alleghany, and Washington Counties in Maryland through fur sealing stations and the University of Maryland Natural Resources Institute at LaVale. Five helminths were found. <i>Travassosius americanus</i> infected 98,4%; <i>Castorstrongylus castoris</i>, 96.8%; <i>Stichorchis subtriquetrus</i>, 50.8%; <i>Trichostrongylus</i> sp., 36.5%; and <i>Gongylonema</i> sp., 11.1%. The unknown <i>Trichostrongylus</i> species is probably a new host record, while the <i>Gongylonema</i> sp. confirms a tentative description by another researcher in 1916 who speculated on the description of another researcher from an 1896 report. The 63 beaver surveyed were infected with at least one helminth, with a mean number of worms per infection of 220.49 (±67.52). Infections ranged between 8 and 837 helminths. The combined number of helminths per infection decreased with age; the sex had little effect, except for <i>S. subtriquetrus</i> where the rate was slightly greater in females (59%) than in males (42%). The 1½ to 3 year old beaver appear to have higher mean numbers of worms per infection with <i>T. americanus</i> and <i>C. castoris</i> than do younger or older hosts. <i>Gongylonema</i> sp. Was more prevalent in older beaver where they had a greater mean number of worms. The males and females of the helminth occurred in the esophagus of the beaver embedded parallel to each other in zipper-like burrows which caused severe irritation of the mucosal lining. <i>Gonglyonema</i> sp. Appeared to be the only helminth which had obvious pathology connected with its presence in beaver. / M.S.

Internal parasites of cattle are capable of causing great economic loss, but the extent of this loss and the savings that can result from control of cattle parasites have only recently received serious attention. For the past several years extension animal husbandmen and veterinarians have reported with increasing frequency parasitic infections in cattle in the State of Virginia. Hence, the Animal Husbandry Department in conjunction with the Animal Pathology Department of the Virginia Polytechnic Institute initiated in the Autumn and Spring of 1953-1954 a survey in the State to obtain information concerning the incidence of bovine parasitism. Three methods have been utilized in diagnosing specific parasitism in domestic animals. Until recently the method commonly employed has been that of post mortem examination. In this type of examination the various digestive organs are tied off in place and then removed for examination for specific parasites. This method, while affording positive information on the one animal sacrificed, could not be regarded as giving sufficient information on the living animals unless a significant percentage of animals were autopsied. The second method is fecal culture which is usually regarded as too time consuming and involving the services of a technician skilled in identification of infective larvae. Lately, differential egg counts have been employed. This method has the advantage of quick diagnosis of mixed infections without loss of animals to slaughter. Therefore, more animals can be examined and a better estimate of the helminth population as a whole can be obtained. The principal disadvantage of this method lies in errors due to mis-identifications of the ova. The 1953-1954 survey employed the differential egg count method. The present study is an outgrowth of the problem of identifying, with reasonable accuracy, some of the commonly occurring species of nematode ova found in samples of cattle feces. / Master of Science

Parasitic infections are ubiquitous, but the consequences to hosts can vary substantially. Variation in the consequences of infection can be related to individual differences in the use of two parasite defense strategies, resistance and tolerance. Resistance entails reducing parasite burden by removing parasites or restricting parasite reproduction. Tolerance involves minimizing the costs associated with a given parasite burden. Genetic variation, environmental conditions, and life history stage can contribute to variation in resistance and tolerance, but the physiological mechanisms that underlie investment in each strategy are not well understood. I proposed that glucocorticoid hormones, which mediate responses to challenges in the physical and social environment in vertebrates, might alter host investment in resistance and tolerance (Chapter I). Glucocorticoids influence a suite of physiological processes including immune function, resource allocation, and tissue growth, all which could alter resistance and tolerance. Using a combination of observational and experimental studies, I test the hypothesis that glucocorticoids mediate resistance and tolerance to infection in red-winged blackbirds (Agelaius phoeniceus) infected with Haemosporidians, including malaria (Plasmodium) and malaria-like (Haemoproteus and Leucocytozoon) parasites. I performed a medication experiment (Chapter II) to identify the physiological consequences of Haemosporidian infection and explored the relationships between glucocorticoids and parasite resistance and tolerance in both an observational field study and a hormone manipulation experiment (Chapters III and IV). Medication treatment effectively reduced Plasmodium burden, increased hematocrit and hemoglobin, and reduced the rate of red blood cell production (Chapter II). In an observational field study (Chapter III), red-winged blackbirds with higher plasma glucocorticoid concentrations maintained higher hematocrit than expected for their parasite burdens, suggesting a positive association between glucocorticoids and tolerance. In this study, I found no support for a relationship between glucocorticoids and resistance. However, experimental elevation of glucocorticoids (Chapter IV) yielded nearly opposite results: the higher of two doses of glucocorticoids increased Plasmodium burdens and caused a decrease in body mass with increasing parasite burden, indicative of a decrease in tolerance. I discuss possible causes of the differences in our observational and experimental studies and the implications of my work for future studies of individual variation in parasite tolerance (Chapter V). / Ph. D. / Why does a cold leave some people bed-ridden, while others can go about their day with only a few sniffles? We can easily see that people react differently when they encounter an infection, but it is not clear why. When faced with an infection, there are two main defense strategies: resistance and tolerance. Resisting infection means reducing the number of parasites or pathogens in the body. Tolerance, on the other hand, refers to reducing the damage or costs that occur during infection. For example, an individual could resist a cold by using the immune system to kill off viruses. If someone tolerates a cold, they might not feel very sick, despite the presence of viruses. Individuals that are more tolerant could be suppressing their own immune response, which can cause the inflammation that leads to a stuffy nose, or these individuals might be repairing damage caused by the virus. Individuals can vary in the extent to which they resist or tolerate infection, but we do not know why this variation exists. In this dissertation, I investigate how the hormones associated with physiological stress might influence resistance and tolerance to malaria and malaria-like parasite infections in red-winged blackbirds. First, I performed a study in which I treated birds infected with a blood-borne parasite with anti-malarial medication to identify the costs of chronic infection. Then I observed the relationships between glucocorticoids (the hormones associated with physiological stress) and estimates of resistance and tolerance in wild red-winged blackbirds. Finally, I used hormone implants to increase stress hormone concentrations in birds held in aviaries, and assessed whether the implants caused changes in resistance and/or tolerance. My results suggest that chronic malaria infection can 5 damage or destroy red blood cells and birds compensate by increasing the rate of blood cell production. In wild red-winged blackbirds, birds with higher concentrations of stress hormones were able to maintain a higher proportion of red blood cells in the blood for a given parasite burden, suggesting they were more tolerant. Stress hormone levels were not associated with the total number of parasites, and thus, we have no evidence for a relationship between the hormones and resistance. When we increased the hormone levels in the aviary experiment, we found nearly opposite results. A high dose of stress hormones caused an increase in the number of parasites and increased the cost of infection. In this dissertation, I discuss possible explanations for the different results in the observational study and the experiment and suggest avenues for future studies.

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The widespread use and subsequent release of pesticides into aquatic environments have sparked concerns about how organisms within these aquatic systems are affected by pesticide pollution. While many studies have examined the effects of pesticides on individual organisms, in a series of experiments, I investigated the effects of a pesticide mixture on members of a complex host-parasite system and on host susceptibility to infection. In my first experiment in the laboratory, I examined changes in survivorship when trematode parasites (Echinostoma trivolvis) and their first intermediate host, Planorbella trivolvis snails, were exposed to a low concentration (10 ppb: 15 ppb) and high concentration (85 ppb: 100 ppb) mixture of atrazine and metolachlor, respectively. There was a significant decline in parasite survivorship in the high concentration treatment at 14 hours, while snail survivorship was unaffected across all treatments. In my second experiment, prior to infection, I exposed the parasites and/or second intermediate hosts, Rana clamitans and Rana sylvatica tadpoles, to the pesticide mixtures and examined subsequent infection levels in the tadpoles. The atrazine and metolachlor mixtures had no significant effects on parasite load in the laboratory. Newly shed parasites were more likely than 10 hours old parasites to infect tadpoles, regardless of pesticide exposure. In my final experiment, I utilized outdoor mesocosms to expose parasites, snail hosts, and Rana sylvatica tadpoles to the pesticide mixture, and I examined differences in parasite load within the tadpoles after two weeks. The pesticides had no significant effect on parasite loads in the field. Overall, my findings suggest the atrazine and metolachlor mixtures used in this study had no significant effects on disease dynamics in a system involving Echinostome parasites, snails, and tadpoles. / Master of Science

Actuellement, l’ectoparasite Varroa destructor est considéré comme la plus grande menace pathogène pesant sur la survie de l’Abeille mellifère (Apis mellifera). En plus d’engendrer des dommages directs aux abeilles par la consommation répétitive de leur corps gras et de leur hémolymphe et par la dépression de leur système immunitaire, les varroas affectent également indirectement les abeilles par la transmission de plusieurs agents pathogènes viraux. En absence de traitements périodiques, la plupart des colonies d’abeilles mellifères s’effondrent dans une période de deux ou trois années suivant l’infestation initiale de Varroas. Face à la pression sélective engendrée par cet Acarien, certaines colonies d’abeilles mellifères ont développé des comportements de résistance. Parmi ces comportements, nous retrouvons le Varroa Sensitive Hygiene (VSH) qui permet aux ouvrières de détecter la présence du parasite dans le couvain d’abeille et de le retirer. De plus, ce comportement est également fortement associé au trait Suppressied Mite Reproduction (SMR), c’est-à-dire, à la baisse du succès reproducteur des varroas dans le couvain d’abeille. Ainsi, les abeilles dotées du comportement VSH sont capables de réduire le niveau d’infestation de leur ruche et de le maintenir à un faible niveau. C’est pourquoi la sélection d’abeilles ayant ce trait comportemental pourrait s’avérer être une solution efficace et durable pour pallier les problèmes engendrés par le Varroa. Cependant, la sélection pour un caractère comporte un certain risque puisqu’il peut advenir que la sélection d’un trait engendre également des répercussions négatives sur d’autres caractères désirables. C’est pourquoi un des objectifs de ce projet est de confirmer la relation entre le VSH et le SMR, et de déterminer les facteurs probables engendrant les problèmes de fertilité du Varroa. Le second objectif quant à lui est de déterminer si la sélection du comportement VSH permet aux colonies de combattre efficacement les varroas sans que cela porte atteinte à la sélection d’autres critères importants en apiculture. / Currently, the ectoparasite Varroa destructor is considered to be the greatest threat to the survival oft he honey bee (Apis mellifera). In addition to causing direct damage to bees through repeated consumption of their fat bodies and depression of their immune system, Varroa also indirectly affects bees through the transmission of several pathogens. In the absence of periodic treatment, most honeybee colonies collapse within two to three years of the initial Varroa infestation. Faced with the selective pressure generated by this mite, some colonies of honey bees have developed a resistance behavior.This behavior, called Varroa Sensitive Hygiene (VSH), allows workers to detect the presence of the parasite in bee brood and remove it. In addition, this behavior is also strongly associated with theSuppressed Mite Reproduction (SMR) trait, i.e., the decrease in Varroa reproduction in bee brood. Thus, bees with VSH behavior are able to reduce the level of infestation of their hive and maintain it at a low level. Therefore, the selection of bees with this behavioral trait could prove to be an effective and sustainable solution to the problems caused by varroas. However, selecting for a trait involves a certain risk since it may happen that the selection of a trait also has a negative impact on other desirable traits.Therefore, the first objective of this project is to confirm the relationship between VSH and SMR, and to determine the likely factors leading to mite fertility problems. The second objective is to determine whether the selection of VSH behavior allows colonies to effectively control Varroa without compromising the selection of other important criteria in beekeeping.