| Pyrethroids are the active ingredient in widely used mosquito coils, aerosol and electric mosquito tablets, all of which prevent mosquito bites. The widespread insect resistance to the insecticidal activity of pyrethorids after heavy use of pyrethroids in disease vector control programs will likely become a major problem. In order to improve the bioactivity of mosquito coils, synergists such as piperonyl butoxide(PBO), octachlorodipropylether(S421), have also been widely applied to mosquito coils. Because octachlorodipropylether will produce carcinogenic substances in the combustion process, it has been forbidden to applied to mosquito coils. Based on past experience with lost synergistic effect to the insecticidal activity of pyrethroids after heavy use of piperonyl butoxide in mosquito coils. Compared with chemical synergist, plant essential oil has vari–bioactivity, such as synergistic effect on pesticide, delaying insect resistance to insecticide, low toxicity and high selectivity. Because of abundance wilding plant resources in China, screening on plant essential oil synergist is a promising research field to improve insecticidal activity. In an ongoing program in the search of plant essential oil synergist against resistant mosquitoes, the focus of the present study was to evaluate bioactiviey and resistance of the field collected Culex quinquefasciatus from Zhongshan, Guangdong, China, against five pyrethroid insecticides, and evaluate bioactivity of 12 kinds of essential oils and essential oils monomer compounds against the field collected Culex quinquefasciatus from Zhong Shan, Guangdong, China. The main results and conclusions are shown as follows:1. Using topical application recommended by WHO, We systematically evaluate the bioactivity and resistance of meperfluthrin, dimefluthrin, teflumthrin, metofluthrin and transfluthrin to Culex quinquefasciatus of Zhongshan, Guangdong, China and sensibility Culex quinquefasciatus. LC50 values of Zhongshan adult mosquito were 12.37, 15.80, 40.11, 62.46 and 66.43 mg/L, sensibility adult mosquito were 5.18, 3.12, 12.93, 17.40 and 16.83 mg/L, the corresponding levels of resistance were 2.39, 5.06, 3.10, 3.59 and 3.95–fold, respectively. The results showed that Culex quinquefasciatus of Zhongshan exhibited very high levels of resistance to dimefluthrin compared with the Lab–susceptible reference strain. However, low to moderate levels for meperfluthrin, teflumthrin, metofluthrin and transfluthrin.2. The knockdown and lethal activity of rosemary essential oil, wormwood oil, eucalyptus oil, citronella oil, basil oil, cinnamon oil, cineole, ?–pinene, ?–pinene, eugenol, cinnamic aldehyde and citronellol were evaluated against Culex quinquefasciatus by airtight fumigation, KT50 values were 5.66, 7.02, 5.76, 13.48, 12.48, 12.34, 4.27, 5.78, 6.52, 23.35, 22.30 and 21.86 min, respectively. Mortality rates were 38.10%, 27.78%, 89.47%, 85.00%, 100.00%, 100.00%, 95.24%, 10.00%, 40.91%, 100.00%, 100.00% and 100.00%, respectively, after 6 h exposure at concentration of 24.2 ?L/L. Mortality rates of basil oil, cinnamon oil, eugehol, cinnamic aldehyde and citronellol were 95.24%, 90.00%, 100.00%, 98.00% and 21.05%, respectively, after 6 h exposure at concentration of 3 ?L/L. The main component of eucalyptus oil, clove oil and cinnamon oil were separated and identified by GC–MS. The results showed that the main component of clove oil was eugenol, and the relative percentage content was 62.79%; The main component of cinnamon oil was trans–cinnamic aldehyde and the relative percentage content was 99.70%; the main ingredient of eucalyptus oil was eucalyptol and the relative percentage content was 69.21%.3. To validate the active ingredient of essential oil, the fumigation activity of eucalyptus oil, cineole, basil oil, eugenol were evaluated at sublethal concentrations of 2.64 ?L/L. The results showed that cineole and eucalyptus oil against Culex quinquefasciatus exhibited strong knockdown activity and weak lethal activity, basil oil and eugenol exhibited strong lethal activity and weak knockdown activity. At the same time, fumigation activity of cineole was stronger than eucalyptus oil, and lethal activity of eugenol was stronger than basil oil. Interestingly, synergistic interaction among plant essential oil and dimefluthrin were evident against adult mosquito. Further, synergistic interaction of dimefluthrin mix with eucalyptol, eugenol, trans–cinnamic aldehyde were detected against Culex quinquefasciatus. The results showed that efficiency coefficient of dimefluthrin mixed with eucalyptol, eugenol and trans–cinnamic aldehyde were 1.2543, 0.9751 and 0.8420, respectively. The efficiency coefficient of dimefluthrin mixed with cineole and trans–cinnamic aldehyde(1:1/m:m) was 1.5709, which was greater than cineole alone. Furthermore, using analog site method to evaluate the synergistic effect, efficiency coefficient was 1.2628. At last, using analog site of 4.5 m3 to evaluate the flavor of mosquito coil, 36 % people feel that the scent is smell nice, 22% people feel that both nearly, 28% people feel the control better than sample, 14% people feel that neither close. The findings also validate the traditional uses of above plant essential oil as pyrethroid synergist against adult mosquito is an important component of the global campaign against vector–borne diseases. |
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