| Background: Insecticide resistance is one of the serious problems for German cockroach control program. This
study was conducted to determine the bendiocarb and Carbaryl resistance mechanisms in German cockroaches using
the piperonyl butoxide (PBO).
Methods: Bioassay tests were conducted with 4 to 6 different concentrations of both insecticides with four replicates
of 10 susceptible strain cockroaches per concentration to determine of discriminative concentration. After
determining discriminative concentration, the result was compared to wild strain. The levels of susceptibility and
resistance ratio (RR) and synergism ratio (SR) were calculated for each five wild strains. Moreover resistance
mechanisms in wild strains were determined using PBO synergist in vivo.
Results: Hospital strains showed different levels of resistance to bendiocarb and carbaryl compared to susceptible
strain. The bendiocarb and carbaryl resistance ratios ranged from 2.11 to 7.97 and 1.67 to 2 at LD50 levels, respectively.
The synergist PBO significantly enhanced the toxicity of bendiocarb and carbaryl to all strains with different
degrees of synergist ratio, 1.31, 1.39, 3.61, 1.78, 1.62 and 2.1 fold for bendiocarb, 1.19, 1.18, 1.12. 1.29, 1.45 and
1.11- fold for carbaryl, suggesting monooxygenase involvement in bendiocarb and carbaryl resistance.
Conclusion: The synergetic effect of PBO had the highest effect on bendiocarb and resistance level was significantly
reduced, which indicates the important role of monoxidase enzyme in creating resistance to Bendiocarb. Piperonyl
butoxide did not have a significant synergistic effect on carbaryl and did not significantly break the resistance. |