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In view of the importance of environmental issuse and the need to preserve the ecological balance essentially in forested areas,a Series of experiments were conducted using two environmentally-safe insecticides,namely,Bacillus thuringiensis (a microbial insecticide with the
brand name of thuricide HP) and diflubenzuron (a safe chemical insecticide with the brand name of Dimilin WP 25).the expriments were conducted each with two different doses under laboratory conditions as follows:
* Temperature:25+ 1 C;
* Relative humidity:73+3%;
* Light: 1000 lux for 12 hours;
*Dosage:5oo and 1000 g/ha for B.thuringensis,and 150 and 200 g/ha for diflubenzuron
Five plots with three replications each were set up, with each replication including 15 Lymantria dispar L.larvae in their last instar.The latter is one of the most important pests of forest and industrial trees and shrubs. The experiments showed that B.Thuringiensis-infected larvae stopped feeding one day after the spraying. Mortality reached 65% within a week,a rate which remained constant up to the end of the second week, which was the end of the experiments. The diflubenzuron-infected Iarvae,however, continued to feed with various de.grees of intensity up to a week after spraying,and thier mortality reached 100% after the experiment period of 14 days. In both cases the mortality rates are based on the average of the two respective doses.
Both insecticides have a satisfactory situation with respect to secondary effects. The effect of B.thuringiensis started after 24 hours and reached its peak of 73.33% on the 9th day, with the lower dosage rate of 500 g/ha. The impact of diflubenzuron started only after the 4th day of the experiment and reached its peak of 100% on the 12th day.Here,100,the higher dosage did not prove to be more effective.