Diluents affecting the toxicity of wettable powder formulations of hexacholorocyclohexane to Sitophilus oryzae Linn. during different periods of storage

Various hexachlorocyclohexane wettable powder (50%) formulations prepared with different types of diluents singlylin mixture of two in 1: 1 ratio and separately with two different wetting agents, viz, Lissapol-D, anionic solid; and HYOXYD AAO, non-ionic liquid under different storage conditions, were evaluated against Sitophilus oryzae Linn. HCH WP formulated with bento-diatomite and Lissapol-D was the most effective formulation. Lissapol-D proved to be superior to HYOXYD AAO in HCH formulations. Lissapol-D seems to act as a deactivator of active sites of clay minerals. W.P. formulations with mixture of diluents were significantly superior to formulations with single diluents. The efficacy of formulation was explained by the physico-chemical properties of diluents, viz., bulk density, moisture content, moisture absorbing capacity, surface area, pH, surface acidity (p^ka), and cation exchange capacity as influenced by the mineralogical characterization. This was revealed by X-ray diffraction analysis of clay diluents. In addition to these factors, the chemical composition of clay diluent, particularly iron content appeared to be contributing factor influencing the efficacy of W.P. formulation. This investigation highlighted the importance of so-called ‘inert’ diluents in the efficacy and stability of W.P. formulations. The validity of accelerated storage as a substitute for long term storage in the determination of shelf-life of wettable powder formulation of a toxicant was suitably indicated.