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

A preliminary cytotaxonomic study of the common Chironomidae in a series of saline waters in the southern interior of British Columbia has been undertaken. The banding pattern of the salivary gland chromosomes, once it had been described, was used as a taxonomic criterion and as an indicator of the relationships between the groups involved. In order to obtain associated stages in the life cycle, the larvae were reared in individual vials. The polytene chromosome analysis revealed seven well defined larval species. The subsequent morphological analysis showed that five of these larval species could usually be separated by their external morphology. However, two cytologically distinct species are morphologically indistinguishable. Recent work on sibling species in Drosophila and Chironomus (Diptera) has shown that sibling species have salivary gland chromosomes with an identical banding pattern but, differ from one another in the frequency of inversions. The present study suggests that the morphologically identical larvae mentioned above are sibling species in larval morphology but are clearly separable by chromosome analysis. The fact that they occur together in the same lake tends to eliminate the view that they are distinct populations of a single species. That there may be more than one species involved in those here considered to be a single taxa, should however not be forgotten. / Science, Faculty of / Zoology, Department of / Graduate

Larvae of Ae. triseriatus mosquitoes were collected from treeholes on the Ball State University campus. These insects were raised to adulthood under laboratory conditions. Newly hatched larvae were raised in deionized water. One hundred twenty-five of instar 1 mosquitoes (group A) were placed into separate baby food jars containing deionized water. These jars were separated into five groups. The pH of the water in each group was adjusted to 3, 4, 5, 6 and 7 with a 70% to 30% sulfuric-nitric acid solution. Subsequent groups consisting of instar 2, 3 and 4 larvae and pupae (groups B, C, D and E respectively) were exposed to the same experimental treatment as that of group A. The effects of each of these pH levels on mortality and development was observed until the insects reached maturity or died.Larvae in water of pH 3 experienced a higher percentage of mortality than mosquitoes exposed to less acidic solutions. A decrease in mortality with age was observed. Mortality of insects in group A was greater than that of any other group. Mosquitoes in group D experienced the lowest mortality.Variations of developmental time for mosquitoes in pH 3 were probably due to high mortality. Developmental time was similar for all groups. Slight variations between these groups may have been due to natural fluctuations in development. The total average developmental time for Ae. triseriatus mosquitoes of this study was 11.12 days.

A little-known approach to toxicity testing--based on negative phototaxis of larval <u>Aedes aegypti</u>--was investigated as a contribution to the search for rapid methods applicable to the field of water pollution control. Zinc and copper were the toxicants tested. All tests were conducted with a standard "synthetic" dilution water. A mosquito colony was established to provide a uniform supply of test larvae. Preliminary tests were performed on the acute toxicity of zinc and copper against <u>A. aegypti</u> larvae, as well as tests on larval growth and development at various concentrations of the metals. For the photomigration toxicity tests, two juxtaposed troughs were used, one containing the test solution, the other a control. Third instar larvae migrated away from a six-watt fluorescent light for two minutes per run. This was repeated at intervals until 50% were unable to migrate 50 cm in 120 sec. Photographs were taken of the larval migrations. From the pictures an empirical criterion was derived (the 40-cm, 60-sec ET₅₀) through a series of graphical interpolations. All inactivation analyses were based on this criterion. From time-inactivation regression lines, exponential toxicity curves were obtained by interpolation. The curves were of an unusual shape, depicting the characteristic nature of the dosage-response. The sensitivity of the inactivation technique was comparable to that of the acute toxicity tests. However, inactivation was far quicker; depending on concentration, it occurred within one to five hours. By all methods used in this study, zinc and copper were judged to be slow-acting and of low overall toxicity. Copper was, however, consistently more toxic than zinc by at least one order of magnitude. The ET₅₀ in 10 ppm Cu⁺⁺ was 147 min.; in 10 ppm Zn⁺⁺, it was 209 min. Some possible improvements in technique were discussed. It was suggested that the photornigration approach to toxicity testing can be of definite practical use to biologists in water pollution control. / Master of Science

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This study investigated aspects of the breeding biology, ecophysiology, morphology, over-wintering and population dynamics of the pre-imaginal stages of members of the Anopheles gambiae complex in northern Natal, South Africa, Investigation of the breeding biology, concentrated on breeding site utilisation by the different members of the Anopheles gambiae complex. Surveillance personnel were unable to locate the breeding sites of Anopheles arabiensis and postulated that location and description of these would offer a unique opportunity for control. The difficulty in locating the breeding sites of An. arabiensis at certain localities was found to be a product of their low density, presumably as a result of the intra-domiciliary, residual insecticide spray programme. The effect of temperature on larval physiology and adult morphology was investigated. terms of their implications Anopheles gambiae complex. The findings are discussed in for anopheline taxonomy and the The effect of temperature on larval growth rates was investigated in both the field and laboratory. The finding of this part of the study indicate that the larval stages play an important role in the over-wintering of populations within the region. The control implications of these findings and winter breeding site localisation are discussed. A theory for the so called 'late season transmission i.e. Apri-May, within the province and southern Africa is proposed. The population dynamics of An. merus were investigated, together with the effect of abiotic factors such as temperature, salinity and rainfall. The effect of sampling bias due to factors such as behavioural avoidance were studied. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1991.

Malpighian tubules of A. dorsalis mosquito larvae, studied in vitro, actively transported magnesium at high rates against concentration gradients as large as 16-fold and transepithelial potential gradients of approximately -l5mV. Fluid secretion rates, determined over 90 minute periods, in the presence and absence of cAMP, indicated that A. dorsalis tubules were viable and had secretion rates of the same magnitude as those reported for A. taeniorhynchus tubules. Having characterized the in vitro preparation of Malpighian tubules, the main hypothesis that Mg²⁺ transport is driven predominately by counter transport with Na⁺ was tested. This hypothesis was not supported by kinetic, Na-substitution, or inhibitor studies. Kinetic and Bumetanide studies suggest backflux of K drives J mg; however, this was not consistently found in other studies. / Science, Faculty of / Zoology, Department of / Graduate