Abstract:

The tannic acid is one of plant allelochemicals. In order to evaluate the potential of tannins in the larval control of noxious mosquitoes, the toxicity of tannic acid to 1st－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 1st－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 with 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 1st－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. 

Key words: Culex pipiens pallens, plant allelochemicals, tannic acid, fenvalerateresistant strain, susceptible strain, development