engleski

Sublethal Dosages of Some Insecticides: an Improvement to the Efficacy of Bioinsecticides

Bioinsecticides based on Bacillus thuringiensis have a slow initial action and their efficacy very rarely reaches the degree of the efficacy of chemical insecticides. At the Agricultural faculty at Zagreb first trials to improve these defficiencies started Kovačević as early as 1958 and were continued later by other scientists (Maceljski, 1974, etc.). In the last years we tried to investigate the possibility to include the use of sublethal dosages of chemicals in the Colorado potato beetle (CPB) resistance management, because the problem of resistance of this insect to OP, OC and P insecticides is very acute in Croatia. We expected to improve the control of the CPB by using ecologicaly safer control methods. By sublethal dosage we consider dosages lower than 10 % of the normal dosage. Low dosages consisting from 10-50 % of the recommended dosage we consider as subnormal dosages. In our twoyear trials with larvae of the CPB sublethal dosages of some OP (chlorpyriphos) and P (alphacypermethrin, lambdacihalothrin and a combination of chlorpyriphos and cypermethrin) insecticides so as one IGR (hexaflumuron) were added to Novodor, an insecticide based on B.t. tenebrionis. The trials were conducted by using the IRAC 7 method. To the recommended dosage of Novodor, dosages containig 1-10 % of the recommended dosage of the previously mentioned insecticides were added. In most cases between the components used in trials an independent synergism was established. Some cases of antagonism were established also. The results of these trials shows a good possibilities to improve the action of the B.t.t. bioinsecticide by using sublethal dosage, but will be continued by including dosages of chemicals lower than 1 % of the recommended dosage.

Colorado potato beetle; bioinsecticides; sublethal dosages

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