m. r. youssefi

German cockroaches are one of the most common indoor pests which could be effective in the transmission of viral, bacterial, and parasitic pathogens. Extensive use of pyrethroid pesticides resulted in resistance in the cockroaches. Studies have showed that bioactive herbal compounds can serve as alternative to chemical pesticides. Aim of the present study was to evaluate lethal effect of carvacrol, thymol, permethrin and cypermethrin on German cockroaches in vitro. In this study, toxic effects of carvacrol, thymol, permethrin and cypermethrin by contact and fumigation tests in dilutions of 0.125, 0.25, 0.5 and 1 µg/cm3 were tested. After 24 h treatment in the contact toxicity test, thymol at all tested doses led to significant lethal effects in comparison to the control (p= 0.004). Thymol at all tested dilutions resulted in significant fumigation toxicity in comparison to the control (p= 0.001). In the present study, thymol in comparison to all other tested compounds exhibited more lethal activity on the German cockroaches.

Insects are the cause of excessive spread of parasites and pathogens. Insect population control faces the challenges of increasing resistance to chemical pesticides and the environmental hazards posed by them. Therefore, the use of natural insecticides is important. The aim of this study was to investigate the synergistic effect of geraniol and betacitronellol on the larvae of Culex Pippins complex.

In this cross-sectional study, samples were taken from the Insectarium of Babol University of Medical Sciences. Yield of geraniol, betacitronellol and their combination in ratios of 4:1, 3:2, 2:3 and 1:4 in a total of 6 groups on the larvae of the third stage of the mosquito culex Pippins complex at concentrations of 0.5, 1, 2, 5, 10 and 20 μg/ml were evaluated with 5 replications. Needle test was used to determine whether the larvae were dead or alive. The LC50 of each group was then recorded after 24 hours.

The highest mortality of larvae belonged to the geraniol group with LC50 equal to 48.1 µg/ml. While betacitronellol with LC50 equal to 49.10 µg/ml had the lowest toxic dose. Among the four combined ratios of geraniol-betacitronellol, the highest toxicity was related to the ratio of 1:4 and the lowest toxicity was related to the ratio of 4:1 with LC50 of 3.32 and 7.71 µg/ml, respectively, and antagonistic effect was observed in all ratios (p<0.05).

The results of the present study showed the antagonistic effects of the combination of geraniol with betacitronellol on mosquito larvae of Culex Pippins complex.