Preliminary Study On The Sound Environmentally Control Technology For Mosquitoes

There is a close relationship between mosquitoes and human life. In addition to direct biting and causing annoyance, mosquitoes even transmit pathogens resulting in human diseases. Now, chemical insecticides still play a leading role in domestic mosquito control. However, a great deal of chemical insecticides using in mosquito control not only pollute the environment, but also mosquitoes rapidly evolve resistance. Therefore, there has been an increased emphasis on the development of other alternative mosquito control technologies. The mosquito species that is targeted by this research are domestic mosquito species Culex pipiens pallens and Aedes albopictus. We emphasized on the larval and adult stages of their life cycle, and set out to exploit the potential sound environmentally technologies for mosquito control. Major research results are as follows:(1) In order to evaluate the potential of tannins in the larval control of noxious mosquitoes, the toxicity of tannic acid to lst-4th instar larvae of the fenvalerate-resistant and susceptible strains of Culex pipiens pallens was investigated in the laboratory, and the impact of tannins on the development of larvae was also observed. The results indicated that the larvae of the susceptible strain was more sensitive to tannins than that of the fenvalerate-resistant strain, and the sensitivity of the former to tannins was 6.4, 4.9, 4.7 and 2.0 times as high as that of the latter for lst-4th instar larvae, respectively. Among larvae of all instars of the two strains, the first instar larvae were always the most sensitive to tannins, while the third instar larvae appeared to be the most insensitive. In the solution of 1 000 mg/L tannins, the survival rate of larvae of the two strains declined as the rearing time. The survivors of larvae exposed to 100-500 mg/L tannic acid solutions had slower development than the control larvae in both strains, and the developmental duration from the first instar to pupation delayed 34.5-38.3 h for the susceptible strain and 59.2-93.4 h for the fenvalerate-resistant strain. Furthermore, the developmental duration of lst-4th instar larvae were significantly different (P<0.05) between the control and the treatment when the concentration of tannic acid for the treatment was 125 mg/L in the susceptible strain and 250 mg/L in the fenvalerate-resistant strain. However, treating the first instar larvae of the two strains with 100-250 mg/L concentrations of tannic acid had no influence on the pupation, emergence and adult sex ratio of the survivors. The results suggested that tannic acid affected mainly the developmental duration of C. pipiens pallens larvae and the degree of influence was related to the susceptibility of larvae to fenvalerate.(2) The attractive and repellent actions of acetone, ammonia solution, sebacic acid, n-heptanoic acid,cyclohexane carboxylic acid, myristic acid, 2, 6-di-tert-butyl-p-cresol, and trieine against the female adults of Culex pipiens pallens were determined by Y-type olfactometer in the laboratory. The results indicated that among the eight compounds tested, compared with control, the 0.1 mg/L n-heptanoic acid solution and the mixture of 10 mg/L acetone solution and 10 mg/L ammonia solution attracted significantly the female adults of C. pipiens pallens. Moreover, the 0.1 mg/L 2, 6-di-tert-butyl-p-cresol solution, and the 10 mg/L acetone solution mixed with 10000 mg/L or 1000 mg/L ammonia solution had significant repellent action to the female adults, in contrast to the control. The other compounds or treatment concentrations had no clear attractive or repellent action against the female adults.(3) Behavioural responses of Ae. albopictus mosquitoes to ethyl butanoate, L(+)-lactic acid solution, dimethyldisulfid, and caproic acid were investigated in a Y-tube olfactometer. The results indicated that 55% ~ 81% of female mosquitoes were activated to fly for all these tests, but only 0.01 mg/L ethyl butanoate solutions, 0.1 mg/L L(+)-lactic acid solution, 0.01 mg/L and 100 mg/L dimethyldisulfid solution were significantly more attractive than control (the former two treatment: PO.01, while the later two treatment: PO.05). The other compounds or treatment concentrations did not differ from the control (P>0.05).(4) Evaluation of mosquito traps baited with Ethyl butanoate, or L(+)-lactic acid solution, 1-octen-3-ol, ammonia solution, 6-methyl-5-hepten-2-one, caproic acid, dimethyldisulfid in various concentrations and several blends were conducted in the field, and the trap was designed by ourselves. But the results showed that all compounds only attracted a few number of mosquitoes (mosquitoes captured were Culex and Aedes, and the numbers were lower than 10). While, the control (rat) was approved to be effective in attractive tests of mosquitoes in the field.