Formulation studies on mosquito coils containing natural pyrethrum
2017
Kawasaki, T. | Watanabe, T. | Kikuta, Y. | Koutani, Y. | Asai, H. | Kawajiri, Y. | Nakayama, K.
The prototype of the mosquito coil dates back to 1890, when an incense stick was invented by blending pyrethrum flower powder with combustible fillers such as plant powders and a binder. Its shape was subsequently improved to a coil form, with a prolonged burning time of 7-8 h, in order to match the sleeping time of humans. Mosquito coils of this type are still widely used globally. With the recent re-evaluation of natural pyrethrum as a favorable insecticidal component, we performed formulation studies on pyrethrum mosquito coils. The results obtained showed that synergist B, N-(2-ethylhexyl) bicyclo[2,2,1] hept-5-ene-2,3-dicarboximide, in combination with natural pyrethrins, was useful for increasing the insecticidal efficacy of natural pyrethrins in coil formulations, suggesting that its physical effects such as promoting the volatilization rate of the active ingredient play a role in the synergistic mechanism, in addition to its insect physiological effects. In further tests, a mosquito coil containing a 1:1 mixture of pyrethrin I-type and pyrethrin II-type pyrethroids exhibited superior efficacy against susceptible and pyrethroid-resistant strains of mosquitoes. These results indicate that natural pyrethrins composed of pyrethrin I-type and pyrethrin II-type compounds have the combined effect of increasing efficacy, particularly against pyrethroid-resistant mosquitoes, while reducing the development of resistance.
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