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

Abstract

Background

Mosquitoes are vectors for several diseases like dengue, chikingunea, malaria etc. The three important mosquito species in India are Aedes aegypti, Culex quinquefasciatus and Anopheles stephensi. Several plant extracts and phytoconstituents have been tested for antimosquito activity. In our present investigation, we have studied, the mosquito larvicidal, pupicidal and ovicidal activities of the successive n-hexane, chloroform and methanol extracts of leaves of Peltophorum pterocarpum (Fabaceae).

Results

The two mosquito species studied were Ae. agypti and Cx. quinquefasiatus. The larvicdial activity on both mosquitoes was in the order methanol > chloroform > n-hexne. The LC ₅₀ values for these extracts were 111.77 and 158.93 ppm (methanol extract), 170.74 and 169.18 ppm (chloroform extract), 219.14 and 203.48 ppm (n-hexane) respectively for both mosquitoes. The pupicidal activity was in the order chloroform > methanol > n-hexne. The LC₅₀ values for these extracts were 226.01 and 204.041 ppm (chloroform extract), 235.40 and 239.50 ppm (methanol extract), 303.07 and 284.04 ppm (n-hexane,) respectively. The ovicidal activity of the extracts against both the mosquitoes studied was not appreciable.

Conclusion

The methanol extract revealed higher larvicidal activity, while the chloroform extract showed higher pupicidal activity for both the mosquitoes. Hence, the methanol and chloroform extracts of the leaves of the plant may be taken up for further studies. This is the first detailed report on the antimosquito activity of the successive extracts of the leaves of Peltophorum perocarpum against the two mosquito species Ae. aegypti and Cx. quinquefasciatus.

Background

Mosquito-borne diseases cause severe threat to public health and economic growth mainly in the tropical and sub-tropical regions of the world [1]. Approximately, half of the world population is at risk of being infected with arbovirus by the end of 2050 [2]. The main mosquito vectors are Aedes aegypti, Culex quinquefasciatus and Anapholes stephensi spreading disease like dengue, chikingunea, malaria, zika virus, filariasis, yellow fever, Japanese encephalitis, West Nile virus etc. Since there are no vaccines available for the majority of these diseases, mosquito control is regarded as a crucial strategy to deal with this problem. In this scenario, mosquito larvae are targeted by synthetic pesticides, insect growth regulators and microbial control agents [3]. Synthetic pesticides eventhough more effective, cause environmental pollution, toxic to humans and animals and nonbiodegrabale. Prolonged use of the synthetic pesticides leads to resistance in the mosquitos [4]. The mortality rates of An. subpictus, Ae. aegypti, and Cx. quinquefasciatus with exposure to cypermethrin (a synthetic pyrethroid pesticide) were 100%, 53.3% with a resistant status, and 81.7% with a tolerant status, respectively [5]. Pesticides derived from plants on the other hand are environment friendly, biodegrable and not toxic to non-target organisms. There are several reports on the plant derived antimosquito agents [6,7,8]. In this communication, we report the antimosquito activity of different extracts of the leaves of P. pterocarpum against Ae. aegypti and Cx quinquefasciatus.

Peltophorum pterocarpum (DC), Baker ex K. Heyne belongs to the family Fabaceae [9]. It is native to Southeast Asia, Australia and found throughout India, including Andaman Islands and Sri Lanka [10]. Eventhough planted as ornamental tree, it has been attributed with several medicinal properties. It is used in the treatment of insomaia, skin disorder, constipation, ringworm, inflammation, muscle sprains, swelling etc. Compounds-like steroids, terpenoids, alkaloids, phenolics, flavonoids and lipids have been reported from the plant. Several pharmacological activities, such as antimicrobial, cytotoxic, antidiabetic, antioxidant, hepatoprotective, cardiotonic etc. have been reported [11,12,13]. The aim of the present study is to carry out mosquito larvicidal, pupicidal and ovicidal activities for the sequential extracts of n-hexane, chloroform and methanol of the leaves of plant. Worldwide, numerous studies have been linked to the discovery and isolation of promising pharmacological chemicals from a variety of herbal plants to combat both long-standing and emerging ailments. A few studies have been carried out for different biological activities on the various parts of P. pterocarpum including mosquitos. But it was noted that the antimosquito activity of the leaves was not explored. Therefore, the antimosquito activity of the leaves extracts of the plant were taken up for further studies.

Methods

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].

$$\begin{aligned} & {\text{Percentage}}\,\,{\text{mortality:}} \\ & \frac{{{\text{No}}.\,\,{\text{of}}\,\,{\text{dead}}\,\,{\text{larvae}}\,\,{\text{or}}\,\,{\text{pupae}}}}{{{\text{No}}.\,\,{\text{of}}\,\,{\text{larvae}}\,\,{\text{or}}\,\,{\text{pupae}}\,\,{\text{exposed}}}} \times 100 \\ \end{aligned}$$

$$\begin{aligned} & {\text{Corrected}}\,\,{\text{percentage}}\,\,{\text{mortality:}} \\ & \left[ {{1}\, - \,{\text{nT/nC}}} \right] \,\, \times \,\,100 \\ \end{aligned}$$

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.

$$\begin{aligned} & {\text{Percentage}}\,\,{\text{Ovicidal}}\,\,{\text{activity:}} \\ & \frac{{{\text{No}}.\,\,{\text{of}}\,\,{\text{unhatched}}\,\,{\text{eggs}}}}{{{\text{Total}}\,\,{\text{number}}\,\,{\text{of}}\,\,{\text{eggs}}\,\,{\text{exposed}}}} \times 100 \\ \end{aligned}$$

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].

Results

In our present investigation, the larvicidal, pupicidal and ovcidal activities of successive n-hexane, chloroform and methanol extracts of the leaves of the plant against the 3rd instar larvae of Ae. aegypti and Cx. quinquefasciatus were studied. The results of the larvicidal and pupicidal activities are given in Tables 1 and 2.

Table 1 Lethal concentration (in ppm) of crude extracts of leaves of P. pterocarpum against the third-instar larvae of Ae. aegypti and Cx. quinquefasciatus

Table 2 Lethal concentration (in ppm) of crude extracts of leaves of P. pterocarpum against the pupae of Ae. aegypti and Cx. quinquefasciatus mosquitoes

The results of the ovicidal activity are given in Figs. 1 and 2.

Fig. 1

Percentage ovicidal activity of crude extracts of leaves of P. pterocarpum against Ae. aegypti eggs

Fig. 2

Percentage ovicidal activity of crude extracts of leaves of P. pterocarpum against Cx. quinquefasciatus eggs

The larvicidal activity of the methanol extract was the highest on both mosquitoes, the LC ₅₀ values being 111.77 and 158.93 ppm respectively for Ae. aegypti and Cx. quinguefasciatus. The chloroform extract and the n-hexane extract showed lesser activity, chloroform being more active than n-hexane extract as shown in Table 1. As far as pupicidal activity was considered, the chloroform extract was more active followed by methanol and n-hexane extract. The LC ₅₀ values for the chloroform extract were 226.01 and 204.41 ppm respectively for both the mosquitoes. However, the ovicidal activity was low for both the mosquitoes even at the highest concentration of 500 ppm. The range of the ovicidal activity was 6.4–24.0%. From Figs. 1 and 2, it is evident that n-hexane and chloroform extracts are equally effective in both mosquitoes while methanol extract was almost inactive.

Discussion

There have been numerous reports of plant extracts having mosquitocidal effects on mosquito vectors. The different responses of distinct mosquito species were influenced by both internal and external elements, such as the plant species, parts of the plant, solvents used for the extraction, the environment where the plants were grown, and the application methods [19]. Othman and Latip [20] found that the most effective antifeedant index (AFI) activity for inhibiting Pomacea canaliculata growth was found in methanol leaf extract of Peltophorum pterocarpum. It acted as an antifeedant and had the highest AFI (46.9%). This explains the larvicidal activity of the methanol extract possibly by antifeedent activity. However, the pupicidal activity was found for the chloroform extract. This may be due to the fact the pupicidal activity is shown not by feeding but by external contact. Bochala et al. [21] found that the methanolic extract of the leaves of the plant also showed anthelmintic activity against earthworms belonging to species Pheritima posthuma (Annelida). It exhibited in a dose-dependent manner, causing short-term paralysis and death. Additionally, the study by Deepa and Remadevi [22] on the methanol extract of the leaves of Lobelia nicotianaefolia also showed highly significant insecticidal activity with mortality of 92% against 4th instar larvae of Hyblaea puera Cramer.

Literature survey of the previous studies of the antimosquito activity of the plant, Peltophorum pterocarpum has revealed three reports. The fixed oil of the seeds obtained by extraction with n-hexane showed moderate larvicidal activity against the 3rd instar larvae of Cx. quinquefasciatus [23]. The larvicidal activity of the ethanol extract of the stem bark was studied against the early 4th instar larvae of Ae. aegypti, Cx. quinquefasciatus and Anopheles dirus. The extract showed good activity with LC₅₀ values of 15.39, 28.12 and 34.19 ppm, respectively [24]. Methanol and aqueous extracts of the flowers were studied for the larvicidal activity against Ae. agypti larvae. No appreciable activity was reported [25].

This is the first report on the detailed larvicidal, pupicidal and ovicidal effects of the three successive extracts of the leaves on the two mosquito species, Ae. agypti and Cx. quinquefasciatus. The investigation revealed the methanol extract showed highest larvicidal activity, while chloroform extract showed highest pupicidal activity against both mosquitoes. The ovicidal activity, however, for all the extracts was not appreciable for both mosquitoes.

Conclusion

The present investigation on the larvicidal, pupicidal and ovicidal activities of the leaf extracts of the plant P. pterocarpum on two mosquitoes Ae. aegypti and Cx. quinguefasicatus revealed appreciable larvicidal and pupicidal activities while the ovicidal activity was not appreciable. The methanol extract showed higher larvicidal activity while the chloroform extract showed higher pupicidal activity for both the mosquitoes. Hence, the methanol and chloroform extracts of the leaves of the plant may be considered for commercial application as antimosquito agent.

Recommendations for future studies

In our present work, only the extracts of the leaves of P. pterocrpum have been studied for larvicidal, pupicidal and ovicidal activities against two mosquitoes vis- Ae. aegypti and Cx. quinquefasciatus. Bioactivity guided fractionation over column chromatography may be carried out to isolate and identify the different active principles. The work may be extended to malarial vector An. stephensi. Further work may be carried on the derivatives of the active constituents. Toxicity on non-target organisms should also be carried out for the extracts as well as the active constitutes.