Thesis (M.S.)--University of West Florida, 2009. / Submitted to the Dept. of Environmental Studies. Title from title page of source document. Document formatted into pages; contains 119 pages. Includes bibliographical references.

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The rise of large scale agriculture in the 20th century created the need for effective strategies to control insect pests. Treatment with chemical insecticides has been a weapon of choice, but the inevitable evolution of resistance has followed in many insect species. Resistance represents a major challenge, not only for agricultural production, but also for environmental preservation and human health. Two major options for resistance have been identified, and these are target-site based and metabolic-based resistance. Much insecticide resistance research focuses on identifying these mechanisms through genetic and molecular analysis. The insecticide lufenuron is the focus of this study. It belongs to a novel insecticidal group called the insect growth regulators, which were introduced in 1970s as highly selective insecticides with low vertebrate toxicity. Resistance to lufenuron in the non-pest species Drosophila melanogaster has been observed in field populations, despite the lack of field usage of lufenuron (Wilson & Cain, 1997; O’Keefe, 1997). This study has taken advantage of this phenomenon to investigate resistance mechanisms in natural populations. At least two detoxification mechanisms were identified. (For complete abstract open document)

Thesis (M. P. H.)--University of Hong Kong, 2007.

Thesis (M. P. H.)--University of Hong Kong, 2007. / Also available in print.

Made available in DSpace on 2014-06-11T19:22:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-04-29Bitstream added on 2014-06-13T19:49:25Z : No. of bitstreams: 1 rossi_ca_me_rcla.pdf: 887311 bytes, checksum: 0aac6ef29470c2188c7f7d4a2bd7179d (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Uma preocupação atual consiste no uso indiscriminado de muitas substâncias sintéticas no controle de pragas na agricultura. Estudos atuais indicam que algumas dessas substâncias podem estar envolvidas em casos de intoxicação de insetos, como as abelhas, que são fundamentais em muitas culturas, devido à atividade de polinização realizada por elas. No Brasil, um dos inseticidas mais usados nas culturas de café, citrus, algodão e cana-de-açúcar é o imidaclopride, que apresenta ação neurotóxica para os insetos. Seus metabólitos circulam por todo o organismo e entram em contato com diversos órgãos. A exposição a doses subletais deste inseticida pode provocar mudanças na fisiologia e no comportamento das abelhas, sendo que tais alterações podem ser mais intensas ou não, dependendo do período de exposição. Dessa maneira, o presente estudo teve como objetivo avaliar os efeitos da exposição crônica a doses subletais (DL50/100, DL50/50 e DL50/10) do inseticida imidaclopride, no cérebro, ventrículo e túbulo de Malpighi de Apis mellifera africanizada. Para isso os órgãos estudados das abelhas expostas e dos controles foram submetidos a análises morfológica, histoquímicas e imunocitoquímica, após 1, 3, 5, 7 e 10 dias de exposição. No cérebro das abelhas expostas foi possível observar alterações morfológicas, histoquímicas e imunocitoquímicas nos lobos ópticos de todos os grupos expostos, enquanto que nos corpos pedunculados observou-se tais alterações apenas no grupo exposto à DL50/10. Já nos lobos antenais as alterações não foram observadas. No ventrículo das abelhas de todos os grupos expostos ao inseticida, a análise morfológica permitiu observar de uma maneira geral um aumento na quantidade de células eliminadas no lúmen, na quantidade de secreção apócrina eliminada no lúmen e na quantidade de halos pericromatínicos nas células... / The indiscriminate use of synthetic chemicals to control pests in agriculture is not a new concern. Recent studies indicate that some of these substances are involved in cases of poisoning bees, which are fundamental in many cultures due to the activity of pollination. In Brazil, an insecticide widely used on crops of coffee, citrus, cotton and sugar cane, is imidacloprid, which is neurotoxic to insects. However, its metabolites circulate throughout the body and come into contacting with another organs. Exposure to sublethal doses of this insecticides causes changes in physiology and behavior of bees, and these changes can be more intense depending on exposure period. Therefore, this study aimed to evaluate the effects of chronic exposure to sublethal doses (DL50/100, DL50/50 and DL50/10) of imidacloprid in the brain, midgut and the Malpighian tubules of africanized bees (Apis mellifera). For this, the organs of treated and untreated bees were subjected to morphological, histochemical and immunocytochemical techniques, dissecting the bees after 1, 3, 5, 7 and 10 days. In the brains of exposed bees it was possible to observe morphological, histochemical and immunocytochemical alterations on optic lobes of all bees, whereas in the mushroom bodies, alterations was observed only in the group exposed to DL50/10. The antennal lobe presented no alterations after the treatment in all doses. In the midgut of all exposed groups of bees, morphological analysis showed in general an increase in the number of digestive cells and apocrine secretion eliminated in the lumen and in the number of peripherical chromatin halos were also increased. The histochemical techiniques confirmed the presence of pyknotic nuclei, showing the presence of nuclear fragments and degenerated areas in cytoplasm of digestive cells. The immunocytochemical technique showed no presence of positive nuclei for Tunel reaction in ... (Complete abstract click electronic access below)

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In the first experiment, sexually immature male and female coho salmon were exposed for 21 days to dietary DDT at a level of 10 or 100 parts per million (ppm), or to methoxychlor at a level of 100 ppm. Exposure to 100 ppm DDT was found to increase the level of liver microsomal Cytochrome P-450 from a control level of 1.32 ± .04 nmoles/1000 mg liver to a level of 1.98 ± .04 nmoles/1000 mg liver, a statistically significant difference (P<.001). None of the treatments were found to affect the hepato-somatic index. In the second experiment, liver slices from sexually maturing male and female coho salmon fed 100 ppm DDT for 21 days or a control diet were incubated with 4-C¹⁴-estradiol-17β in vitro. Metabolites produced were extracted with dichloromethane, separated by thin-layer chromatography and assayed using scintillation counting techniques. Produced in the incubation were estrone, estriol and one other unidentified polar metabolite. DDT treatment was found to significantly increase the amount of estriol and unidentified metabolite produced (P< .001). In the third experiment, sexually maturing male and female coho salmon fed 100 ppm DDT for 21 days or for 7 days or a control diet were injected with 625,500 dpm 4-C¹⁴-estradiol-17β and permitted to metabolize the hormone in vivo. Serial blood samples were extracted, chromatographed and subjected to scintillation counting techniques to obtain values for Metabolic Clearance Rate, Half-life Time and Volumes of Distribution of the injected steroid. It was found that ingestion of DDT had no significant effect upon any of these parameters (P<.001). The pattern of metabolites produced in vivo closely resembled that produced in vitro. The evidence presented in this study suggests that enhancement of the activity of the Mixed Function Oxidase system in coho salmon may occur upon ingestion of an organochlorine insecticide, but that the phenomenon may have little significance in vivo. / Science, Faculty of / Zoology, Department of / Graduate