A field-cum laboratory assessment of the toxicity of spray deposits was undertaken to obtain more precise information than is normally available from field experiments regarding the performance of synthetic pesticides against full grown larvae of Papilla dernoleus attacking Citrus limonia standing field, sprays were used to plants and the toxicities of both fresh and naturally weathered deposits were tested in the laboratory, using full grown larvae from laboratory culture. This work describes the techniques used for the application and assessment of toxicities of the spray deposits and the results of trials with three pesticides. The mean mortality of the larvae, expressed as a percentage and corrected by Abbott’s formula (1925) for the mortality of the controls in each test. The age of the deposits was considered as the best criterion to assess the combined effects of weathering, dilution due to the growth of the leaves, penetration in to the cuticle and chemical change of the deposits. The work showed that organophosphorus pesticide (Parathion) is more effective than chlorinated hydrocarbon pesticides (dieldrin and aldrin).
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