Evaluation of Malathion-Impregnated Sawdust for Control of Bean Weevil (Piezotrachelus varium Wagn.) in Stored Kersting's Groundnut

M.O. Obasi


Eucalyptus (Eucalyptus niphophila L.) sawdust, of particle size 0.425-0.840 mm, was treated with an aqueous solution of malathion 83.6% EC (O.0-dimethyl S-1,2 di (ethoxycarbonyl) ethylphosphorodithioate) at 0.5, 1.0, and 2.0% ai. and assayed at predetermined intervals by chemical and biological methods to determine whether impregnated sawdust was an effective formulation to control insect infestations in stored kerstings's groundnut seed. The chemical assay of malathion residues was done by gas-liquid chromotagraphy and the bioassay by exposure of adult weevils (Piezotrachelus varium Wagn.) to seed previously mixed with malathion-impregnated sawdust.
Significantly (P = 0.01) higher amounts of malathion (4.61 - 12.80 ppm) were transferred into stored seed which was mixed with sawdust initially treated at 2.0% ai. than at 0.5 and 1 .O% ai. at each period of assessment. Similarly, greater quantity of malathion residue was recovered from sawdust treated at 2.0% ai. Sufficient malathion was transferred into seed mixed with 2.0% malathion-impregnated sawdust to cause 100% mortality of P. varium for 32 weeks, and also to prevent emergence of F, adults. Seed mixed with 0.5 and 1.0% malathion-impregnatedsawdust were toxic to P. varium for up to 1 and 16 weeks respectively after treatment. Thus, for seed storage not exceeding4months, effective control of P. varium could be achieved by applying 1 .O% malathion-impregnated sawdust without toxic hazards to consumers. Long-lasting storage of seed would, however, require the use of 2.0% malathion-impregnated sawdust. The relative effectiveness, ease of handling and then economics of the use of malathion-impreganted sawdust indicate its suetability as a formulation material to control storage insects.

Eukalyptussägemehl, präpariert mit Malathion 83,6% EC in verschiedenen Konzentrationen, wurde bei der Lagerung von Erdbohnen gegen Insektenbefall, speziell dem Bohnenkäfer eingesetzt. Die Ergebnisse der verschiedenen Applikationen werden beschrieben. Die relativ gute Wirkung, die einfache Handhabung der Anwendung und die Wirtschaftlichkeit von Malathion imprägniertem Sägemehl ist eine geeignete Formulation um Schäden beim Lagern von Erdbohnen durch Insekten zu verhindern.

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