The prevalence of insecticide resistance in vector species around the world is a continuous threat for any success at mitigating the spread of vector-borne diseases. With a limited arsenal of new insecticides, it is crucial for public health programs to understand the geographic range and the genetic mechanisms of resistance to best approach controlling insect vectors. Insecticide resistance is being increasingly observed in phlebotomine sand fly (Diptera: Psychodidae) populations in both the Old World and New World. Sand flies transmit the protozoans that cause leishmaniasis, a disfiguring disease that kills tens of thousands of people each year. The goal of this dissertation was to have both an applied and basic research focus towards understanding resistance in phlebotomines. I began by comparing in vivo and in vitro methods for blood-feeding two species of sand flies, Phlebotomus papatasi and Lutzomyia longipalpis, in the laboratory, both of which are important leishmaniasis vectors. I investigated the susceptibility of both species to ten different insecticides by calculating lethal concentrations that caused varying levels of mortality. Based on these results, I determined diagnostic doses and diagnostic times for both species to the same ten insecticides using an accepted, but novel, assay for sand flies. Finally, I tested for known mechanisms of insecticide resistance in four artificially resistant-selected colonies of sand flies, as well as tested for novel resistance mechanisms. Through applied research, I developed methods for efficient sand fly rearing and for determination of population resistance to insecticides, tools that have worldwide applicability. Through basic research, I determined that laboratory populations of sand flies have sufficient standing genetic variation needed to survive sublethal doses of insecticides; however, I was unable to develop artificially-selected colonies resistant to these insecticides. My research has generated information to provide new insights into the evolution of insecticide resistance in natural sand fly populations. My results support that resistance development may be possible, but evolutionary challenging, an encouraging finding that may be exploited by vector biologists and public health officials to prevent or slow the development of resistance in sand flies to insecticides

A research report submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Epidemiology and Biostatistics / Background: Malaria causes an overwhelmingly large number of cases and deaths around the globe every year, with over 90% of deaths occurring in sub-Saharan Africa. Namibia is among the sub Saharan countries that have malaria as a major public health problem, affecting most pregnant women and children in the northern regions. Insecticide treated net (ITN) distribution has been expanded in the northern regions since 2005, yet there is low ITN utilization. The associated factors for low ITN utilization are not well established. Objective: This study aimed to determine factors affecting the utilization of ITN among pregnant women in northern regions of Namibia. Specific objectives were to: (1) describe coverage of ITNs among pregnant women in terms of possession; (2) describe the utilization rate of ITN among pregnant women in northern regions; and (3) determine the association between various factors and utilization of ITN among pregnant women. The first study outcome measure was utilization of ITN, defined as an individual pregnant woman who had used an ITN the night before the survey day. The second outcome measure was coverage of ITNs, defined as possession of at least one ITN in each household, irrespective of whether or not it was being used. Methods: A cross sectional study design was used, using secondary data from a nationally representative survey which collected data on malaria interventions in regions of Namibia. The original survey collected data from a representative sample of 3000 households from 120 primary sampling units (PSUs) in nine regions country wide, using a stratified sampling method of two stages. This study targeted pregnant women in four northern regions, namely; Kavango, Ohangwena, Oshana and Omusati, in both rural and urban areas; who participated in the 2009 Namibia Malaria Indicator Survey (NMIS) from 4 April to 10 June 2009. A total of 83 pregnant women were included in the analysis out of 194 pregnant women who were interviewed during the 2009 survey. In the descriptive analyses, we described the demographic characteristics of pregnant women. In the analytic analyses, univariable and multivariable analysis (logistic regression) were conducted. Logistic regression was used to determine risk factors associated with ITN utilization. Results: The utilization of ITN was high (47%) for young women aged 15-24 years old. Overall, 67% of pregnant women aged 15-44 years old slept under bed nets the night prior the survey day. In the univariable analyses, being 35-44 years of age (OR 0.25; 95% CI: 0.07-0.89, p<0.02) and having information about malaria (OR 0.28, 95% CI: 0.09-0.85, p<0.03), were independently associated with ITN utilization. In the multivariate logistic regression model, none of the explanatory variables were significant at the 5% level. The study showed 98.8% overall coverage of ITNs among pregnant women in terms of possession. Conclusion: These findings have implications for malaria interventions in Namibia. While almost all the pregnant women recruited in the study possessed ITNs, a significant proportion did not utilize them. Older women were more likely to utilize ITNs. Interventions to improve utilization among pregnant women should target younger women below the age of 35. Women that had information on malaria were more likely to utilize ITN. Sensitising women about the epidemiology of malaria across Namibia could lead to improved utilization of ITNs. A national malaria strategic plan needs to incorporate targeted reproductive women’s education for malaria control in Namibia.

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The problem of controlling tsetse flies in Africa is an old one. The tsetse fly transmits the trypanosome parasites which cause sleeping sickness in humans and disease in cattle. Because cattle are a favoured food source for tsetse much work has been done looking at the use of insecticide treated cattle as a control strategy for the tsetse fly. Such treatment methods possess many advantages; they are safe and relatively environmentally benign, they can be applied by individual farmers without the need for logistically demanding and costly traditional control programmes and, in addition to tsetse flies the insecticides are effective against a wide range of other harmful cattle parasites. The cost of the insecticide is however a significant constraint to the number of livestock keepers who can afford to employ the technique and as a result many cattle remain untreated. Following the discovery that tsetse had a significant predilection for feeding on the legs and belly of cattle, it was hypothesised that restricting the insecticide to only those areas could offer comparable protection to treating the whole animal. Such an approach would use up to 80% less drug and thus make the treatment per animal much cheaper. In addition, preferentially targeting areas favoured by tsetse, and leaving the rest of the animal untreated, preserves some important ecological balances between cattle and their parasites which traditional treatment methods destabilise. This thesis describes the design, implementation and analysis of a longitudinal study run over 8 months in south east Uganda that sought to compare the effect of applying insecticide to cattle only on the regions favoured by tsetse flies. Cattle were recruited to the study and assigned one of four treatment groups; a whole body application of deltamethrin insecticide pour-on; a restricted application of deltamethrin spray, applied to the front legs, ears and belly; a prophylactic trypanocide injection of isometamidium chloride, and a control group, that received no further treatments. All animals in the study were however cleared using twin doses of a trypanocide diminazene aceturate at the start of the study.

Larvae of the common green lacewing (GLW), Chrysopa carnea Stephens, have been reported tolerant to synthetic pyrethroid insecticides including permethrin (C/T) (3-phenoxybenzyl-3-(2,2-dichlorovinyl)-2,2-dimethyl-cyclopropanecarboxylate), the trans isomer being more toxic than cis. An investigation was performed to determine the possible role of metabolism in this tolerance. Following topical application, GLW metabolized 80% of cis and 71% of trans within two hrs. About 95% of both cis and trans were metabolized by 50 hrs. Metabolism of C/T in vitro was compared to a susceptible insect, the tobacco budworm (TBW), Heliothis virescens (F.). GLW degraded cis 1.7-fold faster than trans, while TBW metabolized trans at a slightly higher rate than cis. When esterases and oxidases were active together or alone, cis and trans were metabolized faster by GLW than TBW. Metabolism of C/T by GLW was primarily oxidative with hydrolysis as a secondary mechanism. Trans is more toxic to GLW apparently because of this isomer's lower rate of detoxication. Several metabolites of C/T, cis-, and trans-permethrin were identified in studies with GLW in vivo and in vitro. It appeared that cis was metabolized more intensively than trans in vivo. The roles of esterases and oxidases in metabolizing C/T, cis-, and trans-isomers were studied in vitro and the following number of metabolites were identified: with C/T--five with esterases plus oxidases, six with esterases, and seven with oxidases alone. With cis--six metabolites were produced when esterases plus oxidases were active, five with esterases, and four with oxidases alone. With trans--esterases plus oxidases produced four metabolites, three with esterases alone, and seven with the oxidases alone. A few unknowns were exhibited in each case. Hydroxylation at the 2'-position of the phenoxybenzyl group seems to be important for GLW tolerance to C/T. Hydroxylation could be the first step in detoxifying C/T and its isomers. The toxicity of trans to GLW could be explained by the limited routes by which esterases acting alone can degrade this isomer; only three metabolites were produced with esterases while seven were produced with oxidases.

Several studies were conducted on spring cantaloupes from 2002-2004 to evaluate a new insecticide, Oberon (spiromesifen) for whitefly control in spring melons. These studies demonstrate that this IGR-like insecticide offers melon growers management alternatives for effectively controlling whiteflies. The results strongly suggest that Oberon has good potential for controlling whiteflies in spring melon crops similar to what can be expected from Courier. Oberon provided 21-28 days of residual control of whiteflies under spring growing conditions when applied early in whitefly population growth. Our studies also indicate that spray timing is important for cost-effective control with both Oberon and Courier. They also suggest that action thresholds based on adult abundance and nymph densities differ for these two compounds depending on whether Admire has been applied at planting.

"Whitefly resistance to insecticides is a constant threat to successful management of sticky cotton resulting from inadequate control of Bemisia whiteflies. A three-stage resistance management program was implemented in Arizona cotton following a severe whitefly resistance crisis in 1995. This program has been highly successful for eight years. Success has been fostered by intensive investments into improved whitefly sampling and treatment decisions, coupled with conservation of natural enemies. This latter component has hinged on limited, strategic use of two insect growth regulators in cotton, use of the neonicotinoid insecticide, imidacloprid, in vegetables and melons, and tactical deployment of non-pyrethroid and pyrethroid chemicals. Statewide monitoring of whitefly resistance to insecticides in cotton, melons and greenhouse crops has permitted annual assessments of the status of whitefly resistance management in Arizona. In this paper we summarize susceptibility of whitefly collecions made in cotton in the 2002 and 2003 seasons and discuss longer term trends in resistance development. No major problems regarding field performance of insecticides against whiteflies were observed or reported in 2002 or 2003. However, monitoring confirmed the early stages of evolution of resistance to pyriproxyfen (Knack®) and showed that whiteflies possessing this resistance could be detected in all cotton-producing areas of the state. Susceptibility to buprofezin (Applaud®/Courier®) has not changed significantly since 1997. Mean susceptibility to synergized pyrethroids (e.g., Danitol® + Orthene®) has increased strikingly on a statewide basis since 1995. However, 50 and 25% of cotton fields sampled in 2002 and 2003, respectively, had resistance levels expected to result in inadequate performance of synergized pyrethroid treatments. Whiteflies from throughout Arizona were highly susceptible to imidacloprid (Admire®/Provado®) and two other neonicotinoid insecticides, acetamiprid (Intruder®) and thiamethoxam (Actara®/Centric®/Platinum®)."