EFFECTS OF DROPLET DENSITY AND CONCENTRATION ON THE EFFICACY OF BACILLUS-THURINGIENSIS AND CARBARYL AGAINST GYPSY-MOTH LARVAE (LYMANTRIA-DISPAR L)

The feeding behavior of gypsy moth larvae exposed to two pesticide deposits (Bt and carbaryl) on oak leaf disks was monitored to determine the relationships between its efficacy and application parameters (droplet density and pesticide concentration). A range of pesticide concentrations and droplet densities (from 9 to 149 droplets/cm(2)) was used to simulate high and low application rates produced by different methods of application in the field. The LD(50) and the LC(50), appeared to be affected by the spatial distribution of the deposit on the leaf surface. Both Bt and carbaryl showed a decreasing LD(50) at increasing time after spray. The LD(50) of Bt decreased from 14.1 BIU/liter to 3.1 BIU/liter between 48 and 144 hours after spray. The results show that feeding inhibition by Bt is more closely related to concentration than to droplet density and dose per unit area with the highest feeding inhibition occurring at 10 BIU/liter at 9 droplets/cm(2). With carbaryl, an increase in both concentration and droplet density was necessary to cause a decrease in leaf area eaten by larvae.