الفهرس 
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Abstract
The present work aimed to study the effect of some nitrogen fertilizers (ammonium sulphate, ammonium nitrate and urea) at different rates of application on some biological aspects of the cotton aphid, Aphis gossypii attacking okra young plants (under semi field conditions) and the corn leaf aphid, Rhopalosiphum maidis attacking maize plants under field conditions. The studied biological aspects were nymphal period, adult period, generation period and number of offspring per adult. The study was extended also to investigate the subchronic effects of nitrate levels in maize grains (descended from the fertilized plants) used as a feed for white rats males. The results obtained showed that nymphal period, adult period, generation period of the cotton aphid and corn leaf aphid were prolonged significantly as influenced by the tested fertilizers. Nymphal periods recorded the averages of 8.02, 8.28, 8.34 days for ammonium sulphate, ammonium nitrate and urea, respectively, comparing with 5.62 days for the control nymphs. The averages of adult periods were 15.78, 15.69, 15.84 days for the above- mentioned fertilizers, respectively, comparing with 12.87 days for the control. Generation periods were also prolonged being 23.80, 23.97, 24.18 days for the tested fertilizers, respectively , as compared with 18.49 days for the generation period of the control aphid. The number of offspring per aphid adult fed on plants fertilized with the tested nitrogen fertilizers were clearly increased recording 23.98, 25.33, 22.52 offspring per adult, respectively, comparing with 14.13 offspring per adult of the control. Nymphal peried, adult period, generation period were prolonged as the application rate of fertilizers increased. Number of offspring per adult was also increased as the fertilizer appplication rate increased. Similar results were also recorded for the corn leaf aphid, wheras nymphal period and generation pertiod were prolonged significantly as influenced by the tested fertilizers; the prologation of adult period was insignificant. Nymphal periods recorded the averages of 7.15, 7.02, 7.16 and 6.39 days for ammonium sulphate, ammonium nitrate, urea and farmyard manure fertilizers, respectively, comparing with 5.05 days for the control nymphs. The averages of generation period were also prolonged being 22.83, 22.17, 21.22, 20.81 days, for the above - mentioned fertilizers, respectively, as compared with 18.48 days for the generation period of the control aphid. The averages of adult period were 15.70, 15.22, 14.20 and 13.77 days for the tested fertilizers, respectively, comparing with 13.26 days for the control with insignificant differences between them. The number of offspring per aphid adult fed on plants fertilized with the tested nitrogen fertilizers were clearly increased recorded 23.28, 21.78, 21.08 and 20.25 offspring per adult of the tested fertilizers, respectively, comparing with 15.00 offspring per adult of the control. Nymphal period and generation period were prolonged as the rate of fertilizer application incerased. Also, the number of offspring per adult took a similar trend, while the adult period not influenced by the rate of fertilizer application. As for the effect of feeding albino rats males on diets differed in its content of nitrate for a period of 90 days, the results showed that the live body weight gain was decreased significantly by the highest nitrate levels ( 300 and 295 mg/ kg diet). As for the internal organs weight ratios; the liver and kidney were influenced by the tested levels of nitrate while spleen, heart, brain, lungs, testes were not influenced. The biochemical parameters such as: liver function e.g., (ALT, AST, ALP, GGT enzymes, total protein, albumin and glucose) and kidney function, e.g., urea and creatinine; the results showed that AST, ALP and GGT were influenced significantly due to the higher rate of nitrate. The plasma protein (albumin) was significantly decreased due to the high level of nitrate, while total protein was not influenced significantly. Blood glucose level was significantly increased due to the nitrae level of 180 mg/ kg diet, while insignificant increases were occurred for the other nitrate levels. The urea was significantly increased due to the high level of nitrate in the diet of rats, while creatinine was not influenced significantly by the low levels of nitrate while influenced significantly by the high levels of nitrate. The histopathological investigations showed an injury in liver, kidney, brain and these injurys were sharp in liver and kidney than in brain.