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<p>  </p> <p>The objectives of this dissertation included comparing the whole gut bacterial profiles of insecticide resistant and susceptible <em>B. germanica</em> and determining how these profiles, as well as the structure and function of the gut microbiome, change in the presence of an antibiotic. Additional goals were to investigate how antibiotic treatment impacts the toxicity of the bait insecticides fipronil, abamectin and indoxacarb, and to determine how gut bacteria, and specifically the enzymes originating within gut bacteria, metabolize and convert ingested indoxacarb into its toxic metabolite DCJW. Findings show that pre-treatment with the antimicrobial compound kanamycin (KAN) led to reductions in resistance levels for fipronil and abamectin, but also increased basal toxicity levels in both resistant and susceptible strains tested. 16S bacterial sequence surveys revealed that resistant and susceptible cockroach strains were more similar before KAN treatment than after, with a stronger dysbiosis effect in the resistant strain. For the insecticide indoxacarb, regardless of strain, roaches treated with kanamycin-infused water in feeding bioassays were more susceptible compared to the control treatment, but in vial (surface contact) bioassays, only susceptible cockroaches experienced a significant shift in mortality. When the frass of indoxacarb-fed cockroaches was analyzed, fewer molecules of the hydrolytic metabolite DCJW were produced with the introduction of an antibiotic (KAN). This result was further corroborated by esterase activity assays of whole homogenized cockroach guts. All results considered, these findings provide novel evidence of microbe-mediated pro-insecticide activation in the cockroach gut. Overall, the results of this dissertation reveal previously unknown relationships between gut microbiota and their insect hosts. These microbiome relationships exposed important cockroach strain differences which may extend to the host population level. Furthermore, this research has connected a change in enzyme activity in the gut microbiome with indoxacarb, a very important marketplace pro-insecticide.</p>

Gong Jun. / "March 2004." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (p. 254-294) / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

M.Sc. / The organochlorine insecticides were amongst the first pollutants shown to cause adverse population effects. The potential adverse effects of these pollutants on wildlife are a cause for great concern. Severities of their effects were sometimes surprising given the low levels of the compounds in environmental compartments such as surface waters and soils. High lipophilicity combined with chemical stability and very slow biodegradation are characteristic features of these toxic Persistent Organic Pollutants (POPs). Regional declines in fish, bird as well as invertebrate populations resulting from long term exposure to POPs such as 1,1-bis (4-chlorophenyl) -2,2,2-trichloroethane (DDT) and its stable metabolite 1,1-bis (4-chlorophenyl) -2,2-dichloroethene (DDE), could be related to some biochemical, endocrine and physiological effects in individuals. Some POPs have been suggested to have negative effects disrupting physiological processes and resulting in alterations of homeostasis, reproduction, development and behavior. Such adverse effects upon populations may be avoided if the potential of chemicals to cause them is recognized before problems arise. The aim of this study was to determine whether or not the ongoing spraying of DDT in the Limpopo Province is negatively affecting the health of aquatic species found in surface water of the area. Extensive research has shown that biomarkers have been very effective in the trace determination of a number of adverse effects caused by metals, and thus, are also being used for POPs. A battery of biomarkers (EROD, CAT and CEA) were used, both in the field and in a controlled laboratory environment, in order to try and determine the long term effects of exposure to low environmentally relevant levels of DDE in the selected area. DDT levels in the biota, water and sediment samples were also measured to determine the possible levels of exposure. Dose-response relationships were most successfully determined by the EROD and the CEA biomarkers in this study. In a controlled laboratory study, a definite effect was noted on the Mozambique Tilapia with increasing concentrations of DDE. In the natural environment, dose-response relationships to DDE exposure were more difficult to quantify as additional chemicals and natural environmental stressors also affect the results.

Ph.D. / The toxicant dichlorodiphenyl-trichloroethane, commonly known as DDT, is a broad spectrum insecticide and is currently banned in most countries due to its toxic effects. However, in some countries restricted use of DDT has been authorized as an effective vector control within malarial control programmes. South Africa is one such country, where spraying of DDT occurs in three provinces including the Limpopo Province, KwaZulu Natal and Mpumalanga. Specifically in the Limpopo Province, spraying of DDT has been ongoing for almost 56 years within the eastern malaria belt of the province. Despite this long term spraying there is still a scarcity of data regarding DDT and its effects on indigenous aquatic organisms in South Africa. Any research regarding DDT will therefore be of the utmost value. It was in this context that the present study was initiated, which primarily aimed to assess the extent of contamination within DDT sprayed areas in South Africa and the associated effects on indigenous species, whilst identifying techniques that could be used in future monitoring of these areas. This assessment was done in the Luvuvhu River catchment at three reference sites and four exposure sites situated within the areas where indoor residual spraying of DDT is done annually. At these sites the extent of DDT contamination within the water, sediment and biota (using the bioindicator pecies C. gariepinus from only the lentic sites) in the Luvuvhu river was evaluated. The results showed that DDT concentrations were well above recommended levels in all three of the measured phases, with the highest concentrations predominantly observed at the Xikundu weir. This site was particularly impacted by DDT due to a combination of its close proximity to the DDT sprayed areas, concentration accumulation from upstream sources and environmental conditions that accentuated contamination. These elevated levels of DDT did, however, not induce significant quantifiable effects in the bioindicator C. gariepinus or in the fish and macro-invertebrate community structures. Specifically, the effects in the catfish, C. gariepinus, were assessed using a range of biomarkers specific to the endocrine disrupting effects of DDT, including indirect measures of vitellogenin (calcium, zinc, magnesium and alkali-labile phosphate (ALP) that are all present on the VTG molecule in high abundances), gonad-somatic index (GSI), condition factor (CF), analysis of covariance (ANCOVA) manipulated gonads, protein carbonyls (PC) and intersex. Although none of these biomarkers could be significantly correlated with the DDT contaminations, DDT was shown to induce a slight sub-organismal effect by slightly inducing the synthesis of ALP and Ca as well as reducing the gonad mass (shown by GSI and adjusted gonad mass biomarkers) and body condition. In contrast, the fish and macroinvertebrate communities showed no conclusive relationship with DDT contamination, using a variety of methodologies, including informal assessments, univariate diversity indices, multivariate statistics, abundance models, fish response assessment index (FRAI) as well as average score per taxon (ASPT) and Ephemeroptera, Plecoptera and Trichoptera (EPT) richness. In conclusion, it was shown that DDT concentrations within the Luvuvhu River only induced effects at the lower levels of complexity, which highlights the importance of the utilisation of biomarkers to measure more subtle long-term effects as compared to the usage of community level effects.

PhD / An important component of fish health is an optimally functioning reproductive system. The Luvuvhu River Catchment in the Limpopo Province, South Africa, is a tropical, high-risk malaria area where 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT), an endocrine disrupting chemical (EDC), has been used annually since 1945 as a malaria vector control. DDT is known to affect testes morphology and motility of fish sperm. As such, testicular histology and sperm motility (kinematic) parameters were studied as reproductive indicators of the reproductive capacity for two wild, indigenous fish species (Oreochromis mossambicus and Clarias gariepinus) from the currently DDT sprayed area. Three field studies were carried out over two years (2007 – 2008), including two high flow (HF) periods and one low flow (LF) period [HF 1 (March 07), LF (October 07), HF 2 (February 08)]. Both species were sampled from three sites on the Luvuvhu River for testicular histology and computer assisted sperm analysis (CASA), during all three field studies. The sites included a reference site outside the DDT sprayed area, Albasini Dam (AD), and two exposed sites within the DDT sprayed area, Xikundu Weir (XW) and Nandoni Dam (ND). CASA, based on open-source software, was used for the first time in South Africa to assess sperm kinematic parameters of indigenous fish species in field conditions. These included percent motile sperm (% MOT), curvilinear velocity (VCL μm s-1), velocity of an average path (VAP μm s-1), straight line velocity (VSL μm s-1), linearity (LIN %), progression (PROG μm), and average efficiency (AVE. EFF.). Water and sediment samples were collected during all field studies from the three sites for metal and EDC analysis. Controlled laboratory studies were also carried out on the sperm of both species, externally sourced from aquaculture farms equipped to breed and raise fish in toxicant free water. The laboratory studies involved in vitro exposure of spermatozoa to two different, but environmentally relevant, concentrations of both DDT (DDT 1: 0.27 μg L-1; DDT 2: 0.5 μg L-1) and 1,1-dihloro-2,2-bis(p-chlorophenyl)ethylene (DDE) (DDE 1: 0.11 μg L-1; DDE 2: 1.0 μg L-1) with the aim to provide data to support the possible outcomes found in the field studies using CASA. Furthermore, peroxidation of sperm lipids was assayed by production of malondialdehyde (MDA) after in vitro exposure of spermatozoa to DDT and DDE. DDT and its metabolites were found in varying concentrations in the water from all three sites (0.1 μg L-1 – 1.2 μg L-1). Levels of dieldrin (3.5 μg L-1) and lindane (9.4 μg L-1) residues were also found at XW in HF 2. The histological results revealed alterations to testis tissue of both species at all three sites. The testes were assessed through the identification of alterations and an organ index was calculated: Testes Index (IT). The index is indicative of the histological response in the respective tissue type. O. mossambicus at XW had the highest mean IT value during LF (7.45 ± 5.73) and for all field studies combined (5.47 ± 4.63), primarily due to the occurrence of testicular oocytes (intersex), where the frequency of prevalence was 72.73% and 58.82% respectively. These results were statistically higher than the laboratory control (C) group. The CASA results showed statistical differences primarily for O. mossambicus, where motility parameters were lower at XW when compared to AD. Laboratory exposures found a decrease in sperm motility (% MOT) between the control (C) group and the DDT 1, DDE 1 and DDE 2 exposed groups for C. gariepinus. No significant differences were seen for lipid peroxidation (MDA). On the other hand, no significant differences were seen in CASA parameters between the control and exposed laboratory groups for O. mossambicus, but there was an increase in MDA production from the control to the DDT 1 exposure group.