Bacillus thuringiensis ssp. tenebrionis Sprays Affect Hatching of Colorado Potato Beetle (Coleoptera: Chrysomelidae) Eggs and Subsequent Larval Dispersal

Abstract

Laboratory and field experiments were conducted to evaluate the effect of Bacillus thuringiensis subsp. tenebrionis (Novodor Insecticide, Novo Nordisk, Danbury, CT) sprays on hatching of Colorado potato beetle, Leptinotarsa decemlineata (Say), eggs and subsequent dispersal of larvae. In laboratory treatments, nearly all egg masses hatch after treatments of 0, 0.2, 1.0, 5.0, and 10.0% (vol:vol) Novodor. Although all larvae from egg masses treated with only water dispersed within 4 d of hatch, larval dispersal and subsequent survival was < 50% in the 0.04% (vol:vol) Novodor treatment, 4% in the 1 and 5% (vol:vol) Novodor treatments, and 0% in the highest Novodor treatment. In the field, freshly deposited egg masses on eggplant were marked; spray applications of Novodor at rates of 0, 1.17,2.34,4.68, and 7.02 liters/ha were applied; and the marked egg masses were monitored over the following 6 d for hatching and dispersal of larvae. Percentage egg masses hatching and dispersal of larvae from the egg mass (survival) declined as the rate of Novodor increased. Plots treated with the high rate (7.02 liters/ha) of Novodor had only 5% dispersal of larvae from treated eggs. These data show that B. thuringiensis subsp. tenebrionis applications on Colorado potato beetle egg masses can be of benefit to growers by killing larvae as they emerge from the egg, thus reducing dispersal of larvae from the egg mass. Implications of this pesticide activity for pest management strategies are discussed.