The effectiveness of mesquite plant, Prosopis juliflora (S.W) D.C. (Family: Mimosaceac), seed extracts against rice weevil, Sitophilus oryzae (L.), rearcd on wheat grains was investigated in the laboratory. The tested plant extracts of P. juliflora in petroleum ether, chloroform, and acetone, effectively controlled adults and their toxicity based on LC95 and LC50 values respectively was in order: acetone (12.0, 5.8ml/kg) < pet ether (8.0, 4.1ml/kg) < chloroform (6.3, 2.2ml/kg). A highly significant oviposition deterency effect (P< 0.05) was found for all extracts at LC50 levels, while at LC95 levels, oviposition was nearly completely inhibited. Thus, progeny emcrgencc was completely suppressed at LC95 levels, also at LCso of acetone extract. Chloroform extract indicated a slow rate of degradation after one month of storage (90% mortality), All tested plant extracts reduced weight loss in wheat grains after 45 days of storage, but chloroform extract was the most effective. Most treatments did not significantly affect water absorption but viability was significantly reduced. Petroleum ether and chloroform extracts caused a significant inhibition effect on acetyl choline esterase (AchE) in adults while acetone extract caused a significant activation effcct. All three different extracts, caused a significant activation effect on phosphases (AcP and AlkP), cxcept for chloroform and acetone extract treatments which caused significant inhibition of AcP in adults. All extracts caused a significant decrease in protein and carbohydrate contents of adults, except the carbohydrate content of adults treated with acetone extract. There was a significant increase in lipid content in adults trcated with all three extracts and significant increase of carbohydrate content only in adults treated with acctone extract.