Evaluation of insectide resistence and biochemical mechanisms in a population of Culex quinquefasciatus (Diptera: Culicidae) from Säo Paulo, Brazil

To establish an insectidical resistance surveillance program, Culex quinquefasciatus mosquitoes from Säo Paulo, Brazil, were colonized (PIN95 strain) and analyzed for levels of resistance. The PIN95 strain showed low levels of resistance to organophosphates [malathion (3.3-fold), fenitrothion (11.2-fold)] and a carbamate [propoxur (3.0-fold)]. We also observed an increase of 7.4 and 9.9 in alpha and ß esterase activities, respectively, when compared with the reference IAL strain. An alteration in the sensitivity of acetycholinesterase to insectide inhibition was also found in the PIN95 mosquitoes. The resistant allele (Ace.1r), however, was found at low frequencies (0.12) and does not play an important role in the described insecticide resistance. One year later, Cx quinquefasciatus mosquitoes were collected (PIN96 strain) at the same site and compared to the PIN95 strain. The esterase activity patterns observed for the PIN96 strain were similar to those of the PIN95 mosquitoes. However, the occurence of the Ace.1r allele was statistically higher in the PIN96 strain. The results show that esterase-based insecticide resistance was established in the PIN95 Cx. quinquefasciatus population and that an acethylcholinesterase based resistant mechanism has been selected for. A continuous monitoring of this phenomenon is fundamental for rational mosquito control and insecticide application programs.

Aspectos moleculares de la resistencia a insecticidas / Molecular basic of insecticide resistance

El surgimiento de resistencia en poblaciones de insectos es uno de los efectos indeseables asociados al uso de insecticidas, y es un buen ejemplo del modo en que ocurren los procesos microevolutivos. En 1908 se documentó por primera vez la existencia de insectos resistentes a insecticidas. Ahora se conocen casos de resistencia en más de 500 especies de artrópodos. Los principales mecanismos que confieren resistencia a insecticidas son penetración cuticular reducida, metabolismo degradativo aumentado y reducción en la susceptibilidad de los sitios de acción. Los métodos de la biología molecular permiten identificar las bases moleculares de esos mecanismos. El propósito de este artículo es reseñar el conocimiento disponible acerca de la biología molecular de la resistencia a insecticidas: mutaciones puntuales en genes de acetilcolinesterasa (Drosophila melanogaster) y del receptor de GABA (varias especies), inserciones en genes de transferasas (D. melanogaster) y del citocromo P450 (D. melanogaster), amplificación de genes de esterasas (Myzus persicae y Culex pipiens / quinquefasciatus complex), cambios que afectan la expresión del gen del citocromo P450 (Musca domestica), y una mutación ligada al gen del canal de sodio dependiente de voltaje (M. domestica)

Changes in serum lipid profile and esterases of rats after sublethal daily doses of dimethoate

Male Wistar rats were injected by dimethoate [10 mg/0.5 ml] daily for 8 successive days. Controls received the same amount of saline. A group of 5 rats were anesthetized at 0, 2, 4, 6 and 8 days of injection. Blood was withdrawn from heart. Serum lipid components and 4 species of serum esterases were assayed for each group. A general decrease in the activities of serum esterases was observed. - A marked decrease also was observed in lipids profile during the 8 days course of experiment