Thesis (M.S.)--Montana State University--Bozeman, 2007. / Typescript. Chairperson, Graduate Committee: Robert K. D. Peterson. Includes bibliographical references (leaves 104-113).

Use of pesticides has been linked to health effects among exposed workers. Organophosphate and pyrethroid pesticides are commonly used to control mosquito-borne diseases in Malaysia. This project aimed to estimate workers' lifetime exposure to pesticides and to examine the relationship between that exposure and health-related quality of life and neurobehavioural performances. A total of 158 workers who had regular contact with pesticides and 176 officebased workers were recruited to the study. Information on past exposure was collected through questionnaire and occupational history interview to help reconstruct workers' historical exposures. Personal inhalation and dermal exposure measurement were carried out to evaluate current pesticide exposure. Subjective inhalation and dermal models were used to allow the estimation of combined pesticide intake for each worker. Neurobehavioural performance was assessed using CANTAB® computerized tests. Total lifetime pesticides intake for exposed workers ranged from 0.006 g to 12,800 g (median (IQR) = 379 g (131, 794)). Estimated dermal exposure accounted for the majority of total lifetime intake of pesticides (median (IQR) = 369 g (128, 772)). After adjusting for age, education, smoking and BMI, exposure to pesticides was associated with lower physical health scores. All of the neurobehavioural performance test scores, with the exception of Reaction Time (RT) and Pattern Recognition Memory (PRM) tests, showed significant differences in relation to total lifetime pesticides intake after adjusting for age, education and smoking. The majority of pesticide-exposed workers indicated a positive awareness about pesticide risk. However, this awareness was not reflected to their selfprotective behaviours such as wearing PPE. Findings from this study suggest that lifetime pesticide intake is associated with physical health and cognitive impairment. It is not clear if this association is causal. Occupational hygiene control measures should focus on reducing the amount of pesticides workers get on their skin due to the high percentage of total intake arising from dermal exposure.

The osmoregulatory function of the larval recta of two saline-water mosquitoes, Aedes campestris and A. taeniorhynchus, was examined. In hyperosmotic waters the rectum was shown to be the site of formation of a concentrated urine by secretion of a hyperosmotic fluid into the rectal lumen. In similar concentrations of sea water, both species produced a rectal secretion having an osmotic concentration and ionic composition similar to that of sea water, with the exception that potassium levels are elevated 18- to 21-fold in the secretion. Osmoregulatory strategies in both species involve the rapid ingestion of the external medium. In taeniorhynchus this drinking rate, (100 nl mg⁻¹ h⁻¹ ) did not vary significantly in salinities between 10% and 200% sea water. It is suggested that two purposes are served by a rapid rate of drinking; 1) dissolved nutrients can be taken up when particulate food is limited and 2) when the uptake of external medium is large relative to the loss of water by osmosis across the cuticle, the concentration of urine necessary to maintain osmotic homeostasis is close to that of the external medium. Rectal function is A. campestris was examined in three media, all with an osmotic concentration of 700 mOsm but varying in their ionic ratios. These media contained the ionic ratios found in sea water and two types of ponds in which A. campestris naturally occur. The larvae were able to survive in all three media, suggesting that the larvae found in one saline environment are not physiologically limited to those ionic conditions. I demonstrated that changes in the relative transport rates of ions in the rectum are very significant in the acclimation process. The rectum was found to be the major site of Na⁺ , K⁺ , Mg⁺⁺, CI⁻ and probably HCO⁻₃ excretion, while the Malpighian tubules are the source of some of the magnesium and almost all of the sulphate in the urine. The ion ratios, exclusive of K⁺ found in the rectal secretion matched those in the external medium, with the exception that an unidentified anion (probably HC0~) substituted for SO₄̿ in (Na + Mg) SO₄̿ medium. A model is proposed showing the sites of ion secretion and uptake in the Malpighian tubules, rectum and anal papillae in all three media. Rectal function in A. taeniorhynchus larvae was examined in 10%, 100% and 200% sea water. In hyposmotic media the rectum does not secrete a fluid and it is postulated that salt and water resorption occur in the rectum under these conditions as in strictly freshwater species. In hyperosmotic media the concentrations of Na⁺ , K⁺ , Mg++ and Cl⁻ as well as the osmotic concentration of the secreted fluid increase with increasing external salinity. Due to the high rate of K+ secretion by the rectum, potassium uptake by the anal papillae is postulated. Sodium and chloride may be excreted at this site as well. An examination of the effect of varying hemolymph concentrations of sodium and chloride on the rate of secretion of these ions in the rectum, showed an allosteric relationship rather than the Michaelis-Mentin kinetics observed with most transport processes (e.g. the Mal-pighian tubules). An in vitro preparation (lacking tracheal and neural con* nections) of the larval rectum of A. taeniorhynchus was used to examine the function of the anterior and posterior rectal segments. These two regions, which differ morphologically, were shown to have separate functions in. vitro, the posterior segment secreting a hyperosmotic fluid while the fluid in the lumen of the anterior segment decreased in osmotic concentration and showed no change in volume. Electrical potential differences were measured across the basal and apical membranes as well as across the entire rectal wall in vivo. Based on these observations in artificial hemolymphs of various ionic compositions, a model is presented of ion transport processes occuring in the posterior rectal segments during the secretion of a hyperosmotic fluid. The model accounts for the ion concentrations and ionic ratios observed in rectal secretion from larvae reared in different media. / Science, Faculty of / Zoology, Department of / Graduate

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Mosquitoes (Culicidae) transmit several parasites and pathogens including the causative agent of malaria, haemosporidians (Haemosporida). Transmission of these agents to and from the mosquito occurs during the collection of a blood meal. Because of this, it is imperative to gather data on current feeding patterns of mosquitoes. Prior to this study there were no published data on current feeding patterns of mosquitoes in Mississippi. Mosquitoes were captured with CDC light traps at eleven sites in two collection years. Engorged females were analyzed for blood meal content, and the vertebrate host was identified to species level in 72 mosquitoes. Previously published haemosporidian data were gathered to compare potential transmission of haemosporidians to and from the vertebrate and mosquito hosts identified in this study.

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