EXTENDING THE RESIDUAL TOXICITY OF BACILLUS-THURINGIENSIS WITH CASEIN-BASED FORMULATIONS

We evaluated the extension of the residual insecticidal activity of Ba cillus thuringiensis Berliner with 2 sprayable formulations based on c asein. One formulation contained native casein in a basic solution (pH > 8.5); the other had a water soluble ammonium salt of casein in tile presence of ammonium zirconium carbonate as a cross-linking agent. Fo rmulations were applied to cotton leaves, Gossypium hirsutum L. 'DES 1 19', in a greenhouse and subjected to simulated rain in a modified spr ay chamber and artificial sunlight from a simulator. Activity was asse ssed based on mortality of neonate European corn borer, Ostrinia nubil alis (Hubner), that were fed treated cotton leaves. Performance of som e formulations was also evaluated against beet armyworm, Spodoptera ex igua (Hubner). Leaves treated with the casein formulations (0.5% wt:vo l) of B. thuringiensis resisted wash-off, often retaining >60% of the original insecticidal activity of unexposed treatments compared with < 20% of the original activity for unformulated and commercially formula ted B. thuringiensis preparations. The casein formulations also provid ed some protection from light-induced degradation compared with unform ulated B. thuringiensis, although the amount of protection was less th an that provided by other experimental formulations.