Mosquito larvicidal, pupicidal and ovidical effects of the different extracts of the leaves of Peltophorum pterocarpum against Aedes aegypti and Culex quinquefasciatus

Collection of the plant material

The leaves of P. pterocarpum were collected from Loyola College Campus, Chennai, Tamilnadu, India, in the month of May 2021 during the flowering stage. The identity of the plant material was confirmed and authenticated by Dr. K. N. Sunilkumar, Research Officer, Department of Pharmacognosy, Siddha Central Research Institute, Chennai. A voucher specimen was deposited in the herbarium of the institute (Authentication Code No: P10032203P).

Extraction of the plant material

Shade dried and coarsely powdered leaves of the plant (1 kg) were extracted successively with n-hexane, chloroform and methanol in a Soxhlet apparatus. The filtered extracts were concentrated in a vacuum rotary evaporator and the dry extracts were stored in air tight containers at 4º C until further use. (Yield: 7.1, 15.8 and 23.2 g respectively).

Insect rearing

The third instar larvae of Ae. aegypti and Cx. quinquefasciatus were obtained from Entomology Research Institute, Loyola College, Chennai. The larvae were reared in chlorine free tap water at 27 ± 2 °C, RH 75–85% and 13:11 L/D photoperiod. The larvae were fed with dog biscuits and Brewer’s yeast in the ratio of 3:2 [14].

Larvicidal and pupicidal assays

WHO guidelines were followed for the evaluation of larvicidal and pupicidal activities of the different extracts [15]. The tested concentrations were 500, 250, 125 and 62.5 ppm with five replicates for each concentration for the three activities. The solutions were prepared as emulsion in 1.0% aqueous DMSO. Twenty larvae or pupae were added to 100 ml of the solution taken in 150 ml plastic containers. 1% aqueous DMSO was used as negative control. Temephos was used as positive control. The mortality of larvae or pupae were recorded at the end of 24 h of incubation. The larvae or pupae were considered dead when no motility was observed when touched with a glass rod. The percentage mortality and the corrected percentage mortality were calculated according to the formulae given below [16].

$$\begin & }\,\,} \\ & \frac}.\,\,}\,\,}\,\,}\,\,}\,\,}}}}.\,\,}\,\,}\,\,}\,\,}\,\,}}} \times 100 \\ \end$$

$$\begin & }\,\,}\,\,} \\ & \left[ \, - \,}} \right] \,\, \times \,\,100 \\ \end$$

where nT is number of larvae or pupae alive after treatment, and nC is number of larvae or pupae alive in control. The corrected percentage mortality formula should be used when the percentage mortality in control was below 5%.

Ovicidal activity

Ovicidal activity was investigated according to the method reported by Elango et al. [17] with a few minor modifications. Twenty freshly laid eggs of Ae. aegypti and Cx. quinquefasciatus were exposed to different concentrations of the extracts in five replicates. The concentrations tested were similar to those for larvicidal and pupicidal activities. The hatchability of the eggs was recorded by viewing under a compound microscope. The percent ovicidal activity was assessed at 120 h post-treatment using the following formula.

$$\begin & }\,\,}\,\,} \\ & \frac}.\,\,}\,\,}\,\,}}}}\,\,}\,\,}\,\,}\,\,}}} \times 100 \\ \end$$

The results were compared with those of the standard control, Temephos.

Statistical analysis

The corrected percentage mortality values for each concentration of larvicidial, pupicidal and ovicidal data were subjected to probit analysis (US EPA probit analysis software, version 1.5) to estimate LC50 and LC90 values. The difference was considered as significant at p ≤ 0.05 [18].

留言 (0)

沒有登入
gif