الفهرس 
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Abstract
This work was carried out to study the susceptibility of Culex pipiens larvae collected from five localities at Sharkia Governorate to malathion and lambda-cyhalothrin. The study was extended also to investigate the development of resistance to these two compounds under a laboratory selection pressure. Some biological changes in the life history of mosquito accompanied the insecticidal selection pressure were taken into consideration. The effect of lambda-cyhalothrin on some biochemical and histopathological changes in albino rats were pursued. The results showed that the highest level of tolerance was recorded for Diarb Negm population followed by population of Salhia, Al-Asher of Ramadan, Zagazig and Faqous. The rate of resistance development to malathion was increased from 1.17-fold in the first generation to 62.45-fold in the eleventh generation. Development of resistance to lambda-cyhalothrin was increased from 1.11-fold in F1 to 100.00-fold in F11. Development of resistance to malathion was associated with inhibition of acetylcholinesterase, which was 13.7 and 3.1% in F1 and F11, respectively. Esterases and glutathione-s-transferase activities were significantly increased when Cx pipiens generations selected with malathion or lambda-cyhalothrin. The highest ratio of esterase activity was scored in the eleventh selected generation with malathion and lambda-cyhalothrin. Also, the highest ratio of GST activity was scored in the eleventh selected generation with malathion and lambda-cyhalothrin, which was 4.9- and 6.8-fold, respectively. Also, selection pressure with malathion and lambda-cyhalothrin was unfavorable for the mosquito biology as it prolonged the larval and pupal duration and reduced the number of egg rafts/female.