Effects of tannic acid on the development of larvae of the fenvalerate-resistant and susceptible strains of Culex pipiens pallens (Diptera: Culicidae)

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