الفهرس Only 14 pages are availabe for public view
 |  | from | 136 |  |  |
| | | from | 136 | | |
Abstract
The Cowpea aphid, Aphis craccivora (Koch), is considered a serious insect attacking several crops. Aphis craccivora has developed resistance to various insecticides. Resistance monitoring in Dakahlia, Qalubia and Bani-Suef field strains were studied. Results showed that the field strain from Dakahlia field strain was resistant to the tested organophosphates, carbamates and neonicotinoids. However, the Bani-Suef field strain exhibited lower levels of resistance. Esterase activity in the three field strains was generally high as the activity ratio ranged between 4.3-7.8, whereas, the activity of both glutathione -s- transferase (GST) and mixed function oxidases (MFO) were moderate in Qalubia and Dakahlia field strains. Therefore, biochemical and molecular studies were carried out to elucidate the mechanisms of resistance in the cowpea aphid to primicarb and thiamethoxam. The thiamethoxam resistant strain showed 48-fold resistance after selection pressure with thiamethoxam for 12 generations. The strain exhibited cross resistance to pirimicarb and carbosulfan and vigor tolerance to malathion and acetamiprid. DEF increased thiamethoxam toxicity to the thiamethoxam resistant strain (ThR) 5.58 times. Biochemical assays revealed that carboxylesterase (CbE) activity was 30 times higher in the ThR strain. AChE activity was 3.68 times higher in R-strain compared to S-strain. Pirimicarb resistant strain showed 47-fold resistance after selection pressure for 12 generations. This strain also exhibited remarkable cross-resistance to carbosulfan, malathion, chlorpyrifos methyl and thiamethoxam. Vigor tolerance levels to fenitrothion and acetamiprid were also found. DEF was a remarkable synergist which showed significant CbE activity. PBO had a synergistic effect by inhibiting MFO activity, and GST had a little role in conferring resistance in PR-strain