Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/17/1996
Publication Date: N/A
Interpretive Summary: Application of Bacillus thuringiensis (Bt) continues to be a safe and effective method for controlling caterpillars on vegetables and other crops. Bt is considered nontoxic and is extremely safe for both nontarget animals and the environment. After nearly 20 years of research on this control tactic, one of the major criticisms continues to be a lack of residual activity after application to field-grown crops. Bt must be eaten by the caterpillars to be effective, and therefore must remain on the plant foliage. Yet, rain easily washes Bt from the plant and requires a subsequent application to maintain insect control. We have developed a new sprayable formulation of Bt that resists wash-off rain. This formulation uses casein (milk protein) that forms a film that sticks to Bt to the plant foliage as the spray droplets dry. Once the formulation dries, the Bt remains effective on the plant even after 2 inches of rain. The use of milk protein retains the ecological benefits of applying a nontoxic insecticide. By improving resistance to wash-off, applications of Bt become more competitive with chemical insecticide applications and may reduce grower dependance on those more toxic control tactics.
Technical Abstract: Two sprayable formulations based on casein were evaluated for extending the residual insecticidal activity of Bacillus thuringiensis. One formulation used native casein in a basic solution (pH>8.5) and the other used a water-soluble ammonium salt of casein in the presence of ammonium zirconium carbonate as a cross-linking agent. Formulations were applied to cotton leaves in a glass house and subjected to simulated rain in a modified spray chamber and sunlight from a Suntest CPS machine. Insecticidal activity was based on mortality of neonate European corn borer, Ostrinia nubilalis (Hubner), fed treated cotton leaves. Leaves treated with the casein formulations (0.5% w/v) of B. thuringiensis resisted wash-off, often retaining greater than 60% of the original insecticidal activity of non-exposed treatments compared with less than 20% of the original activity for unformulated and commercially formulated B. thuringiensis preparations. The casein formulations also provided some protection from light-induced degradation compared with unformulated B. thuringiensis, although the amount of protection was less than that provided by other experimental formulations.