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Abstract SUMMARY Cabbage plants were sprayed with each of three organophosphorus insecticides; malathion, pirimiphos-methyl and prothiofos at recommended dose. All the insecticides used were in commercial emulsifiable concentrate formulations. I - Residues of certain organophosphorus insecticides in and on cabbage leaves: Cabbage plants were sprayed with each of the studied insecticides at recommended dose after formation of plant heads. Outer and inner leaves were sampled and analysed for residues of insecticides. Results indica ted the following: 1 - The largest initial deposit was that of malathion followed by ., pirimiphos-methyl and prothiofos. 2 - Residues of pirimiphos-methyl were the least persistent of the three studied insecticides, followed by malathion, while prothiofos was more persistent. 3 - Detectable residues of the tested insecticides could be estimated in the inner leaves of cabbbage after I, 144 and 216 hrs. of spraying with malathion, pirimiphos-methyl and prothiofos, respectively indicating the lowest ability for penetration into the leaves in case of malathion. 4 - Residual analysis of insecticides in cabbage leaves showed that malathion and pirimiphos-methyl remained on the outer leaves in a rate of unpermitted limits for a period of 288 hrs. after which both insecticides surpassed the - 66- ~-’--,_ ...- ~.~-~---~ ..~~ --’._’~ ------_._----- tolerance limit (3 and 1 ppm for malathion and pirimiphos-methyl, respectively). In case of prothiofos treatment, the insecticide become undetectable after 15 days of spraying. 5 - A ccording to the former result, it was recommended to use the crop commercially after 12 days of spraying in cases of malathion and pirimiphos-methyl and after 360 hrs. (15 days) in case of prothiofos. 11- Side effect of certain organophosphorus insecticides on some biochemical aspects of cabbage plants: Plants were sprayed three times with each of insecticide to study the impact of insecticidal treatments on and in cabbage plants. Effect of the investigated insecticides can be summarized as follows: 1-On chlorophyll content: The effect depended mainly on the spraying frequency. While no significant effect could be observed after the first pesticides application. A gradual and continuous decline was observed after the second and third spray. 2 - On carbohydrates metabolism : A. Soluble, insoluble and total carbohydrates : Generally, soluble carbohydrates content were reduced as a results of pesticide applications. The magnitude of trod decline was greatly dependant on the individual organophosphorus insecticides - 67- --- ------ and frequency of applications. Malathion was more effective than prothiofos or pirimiphos-methyl. Similar effect was observed with concern to the insoluble carbohydrate content as affected by the tested pesticides. All insecticides under investigation induced deplation of insoluble carbohydrate content in treated plants. Data of total carbohydrate content showed more or less similar trends as those noticed for the soluble and insoluble carbohydrates. Malathion was the most effective pesticide in reduction of total carbohydrates content followed by prothiofos and pirimiphos-methyl. It could be also observed that the carbohydrate metabolism as a result of treating cabbage plants with the applied insecticides might be attributed to its inhibition effect on the enzymatic reactions involved in the biosynthesis of the carbohydrates. B. Reducing and non.;.reducing sugars content: 1 - Reducing sugars were delated in cabbage plant leaves due to insecticidal treatment. Reduction was dependent on individual pesticide and the sampling date under the different frequencies of application malathion was the lowest effective pesticide, followed by pirimifos-methyl and prothiofos after the first and second sprays. While, after the third application, prothiofos was the lowest effective pesticide followed by malathion and pirimiphos-methyl. - 68- --- --~- ------- - -- ----~ -- - - - - -- - - -- - _._~_ .. ~~------~ 2 - Non-reducing sugars content, significant reduction was observed in cabbage leaves after the first spray with all of the studied pesticides, but no pronounced differences could be observed between the values of the treated plants. Malathion was the most effective insecticide to reduce decline in the non-reducing sugars content after the second and the third spray as compared with either pirimiphos-methyl or prothiofos. III - Absorption and Translocation of C14-malathion in laboratory : Results indicated that the C14-malathion was hardly translocated inside tissues of cabbage leaves. It is well know that malathion is classified under the quasi-systemic compounds (Hassal, 1981). This group is characterized to have low solubility in water and accordingly hardly to penetrate into leaves. |