Call number: LD2668 .T4 1950 S736 / Master of Science

Call number: LD2668 .T4 1950 S776 / Master of Science

Call number: LD2668 .T4 1958 E32 / Master of Science

A thesis submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science Johannesburg, 2014 / Southern African pyrethroid resistant and insecticide susceptible laboratory colonies of the malaria vector Anopheles funestus were investigated to further understand the phenotypic expression of pyrethroid resistance and to establish at which life stage resistance was selected. Pyrethroid resistance levels of larvae and adults were assessed at the larval and adult life stages using WHO larval and CDC bottle bioassays. Subsequent resistance levels were then assessed following targeted selections at each life stage. Tests for an association between cuticle thickness and pyrethroid resistance were based on cuticle thickness measurements using scanning electron microscope imaging of prepared tissue sections. It is concluded that pyrethroid resistance in southern African An. funestus is only expressed in the adult life stage, and that selection for this phenotype can only be achieved by exposing adults. It also concluded that pyrethroid tolerant or resistant females are likely to have thicker cuticles than less tolerant or susceptible females.

Anopheles funestus Giles is a major vector of malaria in Africa and pyrethroid resistance observed in this species has disrupted malaria control in southern Africa. Metabolic detoxification, based on the overproduction of cytochrome P450s, specifically CYP6P9 and CYP6P13, was identified as the principal resistance mechanism in both field and laboratory populations. This project aimed to characterize this resistance mechanism further, both on a molecular as well as a biochemical level. Biochemical analysis on total P450 activity levels revealed a 25.5-fold increase in the resistant strain compared to a pyrethroid susceptible strain. Analysis of the effect of pyrethroids on mRNA expression of three P450 genes showed that two of them (CYP6P9 and CYP6P13) as well as Cytochrome oxidase I (COI) was induced. HPLC analysis using a heterologously (recombinant) expressed CYP6P9 enzyme, showed that CYP6P9 was able to metabolize the pyrethroid permethrin and that it was catalytically efficient. Immunoblotting revealed no significant variation in CYP6P9 protein abundance between the different An. funestus colonies. Although an approximate molecular weight (≈Mr) of 58kDa was predicted for CYP6P9, two fragments were detected at ≈Mr 52,000 and ≈45,000. The smaller fragment was very likely a result of proteolytic degradation. Statistical analysis revealed there was no significant difference in CYP6P9 protein expression between strains or sexes. Although CYP6P9 mRNA is over-expressed it is important to assess the abundance of protein as well when elucidating whether a gene and its protein are important candidates in resistance. Differences in pyrethroid resistant or susceptible profiles of An. funestus colonies could be related to enzyme affinity for substrate and stability of CYP6P9 protein however; it is recommended that further studies need to be done before any conclusions can be drawn. CYP6P9 in An. funestus is a major candidate in conferring pyrethroid resistance and the pyrethroid resistant strain is able to metabolize the pyrethroid permethrin.

Wing-keung Liu. / Thesis (M.Ph.)--Chinese University of Hongkong. / Bibliography: leaves 96-106.

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Orientador: Wilson Badiali Crocomo / Banca: Carlos Gilberto Raetano / Banca: Adriana Mascarette Labinas / Resumo: A localização das lagartas de Spodoptera frugiperda no interior do cartucho-do-milho, muitas vezes, dificulta a absorção da dose de inseticida necessária a sua morte, de tal forma que uma porcentagem significativa de insetos absorvem doses subletais, sofrendo evidentemente alterações na sua biologia e capacidade reprodutiva. Dessa forma, esse trabalho se propôs a verificar a ação de diferentes concentrações de clorpirifós, deltametrina e lufenuron no desenvolvimento larval e performance biológica de S. frugiperda em dieta artificial e natural (folhas de milho) sob condições controladas (em temperatura de 25 +/- 2ºC, umidade relativa de 70 % e fotofase de 14 horas). Folhas de milho foram mergulhadas em soluções contendo clorpirifós nas concentrações 0,15; 0,25; 0,35; 0,50; 0,75; 1,00; 2,00; 4,00; 8,00; 16,00 e 32,00 ppm, deltametrina nas concentrações 0,20 e 0,40 ppm e lufenuron nas concentrações 0,20; 0,50 e 1,00 ppm, em seguida fornecidas para as lagartas, 48 horas após a eclosão. Também foram preparadas dietas artificiais específicas para S. frugiperda contendo os mesmos inseticidas nas respectivas concentrações, onde foram inoculadas lagartas com 48 horas de idade. As observações de mortalidade e desenvolvimento foram realizadas em dias alternados e os dados comparados ao tratamento testemunha, sem tóxico. Verificou-se que as lagartas que se alimentaram tanto em dieta artificial quanto no alimento natural contaminado pelos inseticidas deltametrina e lufenuron não atingiram a fase de pupa, no entanto, muitas lagartas permaneceram vivas por mais tempo do que o período de duração da fase larval da testemunha. Os tratamentos com clorpirifós, apesar de provocarem uma alta mortalidade de lagartas só inviabilizaram a obtenção de adultos a partir da concentração 8,00 ppm. Mesmo nas doses menores, ...(Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The localization of Spodoptera frugiperda larvae in the inner part of maize whorl, turns difficult the absorption of the necessary insecticide dosage to provoke insect mortality, what means that in field conditions, a significant percentage of the insects absorbs sub-lethal dosages, showing evident modifications on their biology and reproduction capacity. This way, the aim of this research was to verify the action of concentrations chlorpyrifos, deltamethrin and lufenuron on larval development and on the biological performance of S. frugiperda fed on artificial and natural diets. Maize leaves were dip in solutions of clorpyrifos at 0.15, 0.25, 0.35, 0.50, 0.75, 1.00, 2.00, 4.00, 8.00, 16.00 and 32.00 ppm, deltamethrin at 0.2 and 0.4 ppm and lufenuron at 0.2, 0.5 and 1.00 ppm. These leaves were immediately offered to 48 hours larvae. Artificial diets, specially developed for S. frugiperda, were also prepared containing the same insecticides at the same concentrations to receive larvae with 48 hours old. The observations of mortality and development were obtained every other day and the data were compared to a check treatment, with no insecticide. It was possible to verify that the larvae fed on artificial or natural diets containing deltamethrin and lufenuron, did not reach the pupal stage, however, many of them stayed alive for a period superior than that observed for the check treatment. The clorpyrifos treatment, dispite its high larval mortality, turned difficult the obtaining of adults from concentration of 8.00 ppm on. Even at low dosages, many survival larvae died during the pupal phase; only for 16.00 and 32.00 ppm the larval mortality reached 100%. When insects are exposed to sub-lethal dosages of insecticides during their larval period of development, they can increase their life cycle, even when they do not afford the insecticide action, nevertheless, those insects that reach the adult stage, do not show any life cycle modifications. / Mestre

In the Lower Rio Grande Valley of Texas, dipterous leafminers cause damage to pepper crop by destroying small plants (excessive mining), reduction of yield, and by vectoring plant diseases. The objectives of the present research were to identify leafminers species, which cause damage to peppers in South Texas, their associated parasitoid guilds and to evaluate the efficacy of abamectin, novaluron, spinetoram and lambda-cyhalothrin against leafminers as well as their effects on the parasitoid complex. Field surveys were conducted on various pepper varieties in different cities of South Texas. Insecticide evaluation was carried out on field plots in Weslaco TX using the different insecticide treatments and water. To determine the insecticides? lethal effects on adult leafminer parasitoids, Neochrysocharis formosa and Ganaspidium nigrimanus, laboratory bioassays, such as topical insecticide application, pesticide intake and residual effects were performed. The surveys suggested that the leafminers causing the most damage to pepper crops in South Texas is Liromyza trifolii, which represents more than 99% of the collected and identified species. Twenty parasitoid species, of four different families, were found to be attacking L. trifolii on pepper plants in the field. Novaluron was the most effective insecticide in controlling L. trifolii, followed by spinetoram and abamectin. Lambda-cyhalothrin was the least effective, showing L. trifolii tolerance to the compound. In field evaluation novaluron showed the lowest parasitoid: leafminer larvae ratio and parasitoid diversity index. In contrast, novaluron had the least impact on adult parasitoids in laboratory bioassays compared with other treatments (abamectin, spinetoram, lambdacyhalothrin). The lambda-cyhalothrin showed negative effects only to Ganaspidium nigrimanus in topical assays, but in the residual assays it had negative effects on G. nigrimanus as well as N. formosa. On the other hand, abamectin showed negative effects on N. formosa and G. nigrimanus in the topical and intake bioassays and negative effects on G. nigrimanus but no-effect on N. formosa in the residue bioassay. Furthermore spinetoram showed negative effects on N. formosa and G. nigrimanus in all bioassays carried out in the laboratory. Leafminer species, parasitoid species composition, efficacy of insecticides, effects of insecticides on parasitoids and development of tolerance to lambda-cyhalothrin by L. trifolii and N. formosa were discussed.

No description available.