Determination of insecticidal potential of selected plant extracts against fall armyworm (Spodoptera frugiperda) larvae

1. Introduction

Maize (Zea mays L.) from Poaceae family was cultivated in South America before venturing throughout the world [1,2]. Afterwards it spread to China, Asia, Europe, Russia, Canada, USA, Mexico, and Pacific Islands. Maize ranks 3^rd most economically valuable cereal crop worldwide, following wheat and rice, because of its versatile applications in human and animal nutrition, biofuel production, and construction materials [[3], [4], [5], [6]]. Diseases, insect pests, vegetation’s, birds, nematodes, and environmental factors have the potential to substantially reduce the crop yield up to 75 % [7].

Spodoptera frugiperda (Lepidoptera: Noctuidae), also known as the fall armyworm (FAW), is a notorious pest that is native to North America. FAW feeds on more than 350 different plant species, with maize being the main food source [8,9]. S. frugiperda was reported first time during March 2019 from a number of locations in Sindh Province, Pakistan, with the exception of upper Sindh, Larkana, Jacobabad, and Shikarpur [10]. S. frugiperda predominately cause damage by feeding on both vegetative and reproductive parts of host plant. Developing effective control methods for insect infestations is elusive without an in-depth understanding of their life cycles. The habitat of the fall armyworm influences its life cycle. Approximately 30 days are required in summer season at 28 °C temperature for the completion of FAW life cycle [11]. However, in the spring and winter, this time can extend to 60–90 days. Globally, chemical, biological, and botanical strategies for controlling insect pests have been implemented. Synthetic insecticides have emerged as a highly efficient and economically convenient method to immediately combat FAW [12,13]. However, they have adverse impacts on the biological control agents, environment, and contribute to the development of insect pest resistance. S. frugiperda has become resistant to 41 different molecules, which makes it more challenging to get rid of them [14,15].

In order to mitigate pollution to the environment and combat insecticide resistance, it is necessary to develop a sustainable and resilient method of pest management [16]. Pesticides derived from plants are regarded as ecologically sustainable due to their low toxicity towards non target organisms and biodegradability [[17], [18], [19]]. Therefore, these plant based insecticides may be included in the integrated pest management module [20]. Numerous studies have been performed to identify plant sources of safe insecticides, in response to the increased advocacy for their use. Tetranortriterpenoid compound also known as azadirachtin, which is similar to an asteroid. It is extracted from the Azadirachta indica and has been recognized as a major insect repellant in vegetables [21,22]. Furthermore, the significance of neem in pharmaceuticals, agriculture [23], toiletries, and medicine, has significantly increased due to its abundant bioactive compounds [21]. Research has demonstrated that neem possesses a range of beneficial characteristics, including insecticidal, antifeedant, antiimplantation, antifungal, antiallergenic, antidermatic, antiviral, anti-inflammatory, larvicidal, antipyorrhoeic, and nematicidal effects [21,24].

Citrullus colocynthis has been documented for its insecticidal properties against several pests that infest stored grains and other field crops. Furthermore, it possesses an inherent capacity to repel pest infestation [25,26]. This plant exhibited repellent, antifeedant, and infertile properties against many pests [[27], [28], [29]]. An Australian hardwood tree species, Eucalyptus globulus has accomplished worldwide distribution due to its advantageous features such as the beneficial aspects of its leaves and versatility for pulpwood production [30]. The essential oil of Eucalyptus is recognized for its insecticidal properties [31]. Trogoderma granarium (Everts, 1898) (Coleoptera: Dermestidae), among numerous insect species that infest stored products, is susceptible to the toxicity of E. globulus oil in many research studies [32,33]. Volatile compounds such as limonene, α-pinene, lanalool, and 1,8-cineole are present in them, which enables them to kill insects [34].

The antifeedant activity was observed in aqueous crude extracts of tobacco (Nicotiana tabacum) leaves against FAW larvae [35,36]. Significantly, the larvae exhibited the highest mortality when exposed to the extracts at a concentration of 50 % [37]. Recently, Cannabis sativa has received interest as a conceivable alternative for application as a pesticide [38]. In addition to the widely recognized cannabinoids, Tetrahydrocannabinol (THC) and cannabidiol (CBD), the plant produces around 500 compounds, which include other cannabinoids, terpenoids, and flavonoids [39]. Currently, the specific compounds and processes through which C. sativa achieves its insecticidal effects are still unclear. Nonetheless, interactions between specific compounds as well as the pharmacological activities of terpenes and cannabinoids may be involved [40]. The purpose of this study was extraction, characterization and evaluation of insecticidal potential of native plant extracts against the third instar larvae of S. frugiperda.

2. Materials and methods

2.2. Preparation of plant extracts

Six native plant species were collected from various regions of Faisalabad, Punjab, Pakistan, as shown in Table 1, brought to the laboratory and washed extensively with tap water. The leaves/fruit were shade dried (30 ± 5 °C; 10 ± 2 RH) and coarse grinded by using an electric grinder (GRT 1500B). Soxhlet apparatus (J.P. Selecta, s.a; Serial #. 0481090) was used to prepare plant extracts, and ethanol (Sigma, 99.9 %) served as extraction solvent. The thimble was filled with a fine powder of each plant extract, weighing 50 g. A 250 mL volume of ethanol was used as a solvent. The source of heat was a heating mantle that was operating at a temperature of 60 °C. The aforementioned process was repeated multiple times over 13–15 h to complete the extraction. Rotary evaporator (Scilogex RE 100-S) equipped with a vacuum pump was used to purify the ethanolic plant extracts. After rotary evaporation, obtained yield of A. indica, E. globulus, P. hysterophorus, C. sativa, C. colocynthis and N. tabacum was 30 g, 33 g, 28g, 25g, 21g and 20g respectively. The plant extracts were kept at 4 °C in hermetic dark glass containers of 50 mL capacity until their use in the toxicity bioassays.

Table 1.

Comprehensive overview of the plant samples collected from Faisalabad.

Sr. No.	Scientific Name	Vernacular Name	Diagrams	Family	Parts used	Coordinates
1	Azadirachta indica	Neem		Meliaceae	Leaves	31.40429° N, 73.05077° E
2	Eucalyptus globulus	Sufaida		Mayrtaceae	Leaves	31.40170° N, 73.05208° E
3	Parthenium hysterophorus	Gajar booti		Asteraceae	Leaves	31.40210° N, 73.04936° E
4	Cannabis sativa	Bhang		Cannabaceae	Leaves	30.99106° N, 72.87367° E
5	Citrullus colocynthis	Kortuma		Cucurbitaceae	Fruit	31.40166° N, 73.04918° E
6	Nicotiana tabacum	Tobacco		Solanaceae	Leaves	30.99155° N, 72.87339° E

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3. Results

4. Discussion

Plant extracts are used in pest management due to their noteworthy effectiveness against various stages of the insect pest life cycle. Botanical insecticides provide effective and eco-friendly solution to control FAW [44]. Current study demonstrated the potential of plant extracts against FAW. The results of present research demonstrated that higher concentrations and prolonged exposure period of plant extracts showed higher mortality of fall armyworm. Plant based insecticides can be a sustainable alternative to control fall armyworm. Neem leaf and seed extract was found be highly toxic against fall armyworm at different concentrations [21]. Azadirachtin induced 96.7 % mortality among 2^nd instar larvae of FAW after exposure of 120 h [43]. Neem leaf extract was found to be more toxic against fall armyworm larvae at 100 ppm. It indicated that mortality rate of fall armyworms was directly correlated with the increased concentration of plants extract and the duration of exposure [45]. Our present study demonstrates that A. indica is very effective botanical extract against FAW as it induced 64 % mortality of FAW 3^rd instar larvae after 24 h of plant exposure.

The implementation of biopesticides provides an unconventional method for promoting the development of an ecosystem while preventing the detrimental impact on beneficial natural insect fauna and non-target pests. Hassam et al. [46] reported the toxicity levels of C. colocynthis seed extract against the populations of Erias vitella under the laboratory conditions. Results showed that LC₃₀ and LC₈₀ concentrations (ppm) of the methanol-based C. colocynthis seed extract was effective against E. vitella first instar larvae. The treated samples showed prolonged larval and pupal stages compared to the untreated ones. Our results demonstrated that C. colocynthis was very effective as compared to the other plant extracts against the third instar larvae of fall armyworm while maximum mortality was caused in the positive control. The current results indicate that botanical insecticides derived from C. colocynthis extracts have advantages in terms of promoting ecosystem sustainability and can be included into insect management programs, ensuring environmental safety. The highest concentration of C. colocynthis (400 ppm) caused 60 % mortality of FAW larvae after 72 h of exposure duration. Similar to our study, Ahmed et al. [27] reported that 20 mg/mL of C. colocynthis induced 76.67 % mortality among cabbage aphid after the 48 h of treatment. The mortality rate is almost similar, there is little difference that may be due to the concentration of plant extract, and laboratory conditions.

Sakadzo et al. [37] assessed the biological activity of N. tabacum leaf extract against fall armyworm at Great Zimbabwe University under laboratory conditions. The results demonstrated that pure aqueous leaf extracts of tobacco showed antifeedant activity ultimately resulted in FAW larval mortalities considerably higher at the maximum dose of 50 % (p < 0.05) compared to the minimum dosage of 25 % and the negative control after a duration of 20 h. Sakadzo et al. [37] reported that N. tabacum can serve as a viable substitute for synthetic insecticides in controlling the FAW. The LC₅₀ values of N. tabacum were 1517.811, 938.740, and 720.980 ppm after 24, 48, and 72 h, respectively. Our results are more similar to another previous study conducted by Kardinan and Maris [47] as 40 % mortality of FAW was by N. tabacum in both previous and present study. Based upon this context, it can be concluded that tobacco leaf extract can serve as an alternative agent against the synthetic insecticides to control the fall armyworm.

The methanolic extracts of P. hysterophorus and A. adenophora were found to be effective against fifth-instar larvae of S. frugiperda after 72 h, with LC₅₀ values of 5.92 % and 7.82 %, respectively. The efficacy of P. hysterophorus antifeedant action against the fall armyworm was found to be better than that of A. adenophora [48]. The present study is also relied on P. hysterophorus leaf extract to assess its efficacy against the third instar larvae of S. frugiperda. The results demonstrated that it can be an effective alternative to synthetic insecticides in controlling the fall armyworm. The LC₅₀ value of P. hysterophorus was 1686.344 ppm after 24 h, followed by 1113.803 ppm after 48 h, and 320.027 ppm after 72 h.

Arey [49] assessed the toxicity of C. sativa extract against the fall armyworm larvae. A high level of mortality was recorded because of ingesting leaves treated with C. sativa leaf extract. The results of current study demonstrated the efficacy of an ethanolic leaf extract of C. sativa against third instar larvae of fall armyworm. The extract showed a LC₅₀ value of 1517.811, 938.740, and 334.759 ppm after 24, 48, and 72 h, respectively. Up to our knowledge, no study has reported the percent mortality of C. sativa against the fall armyworm. Findings of Prvulovic et al. [50] demonstrated that the highest tested concentration (2 %) caused 42. 5 % mortality of Plodia interpunctella larvae after the 72 h of exposure period. Their results are in line with our study. According to our study, 44 % mortality was induced after exposure of 200 ppm concentration, while 56 % is induced due to the highest concentration (400 ppm) of FAW third instar larvae after 72 h post-treatment.

E. globulus induced 54.51 %, 9.76 %, and 29 % of the mortality of larvae after 24, 48, and 72 h, respectively [51]. Our research results showed that E. globulus at 400 ppm concentration caused 28, 36, 48 % mortality of fall armyworm third instar larvae after 24, 48, and 72 h, respectively. Following the 24, 48, and 72-h, the LC₅₀ values were 1011.981, 815.120, and 518.438 ppm. The findings of the study performed by Anwar et al. [52] are also consistent with the findings of our study.

The plant extracts that demonstrated the greatest efficacy against the fall armyworm were subjected to GC-MS analysis to identify specific compounds present in them, as previously described in numerous studies by Andjani et al. [53], Ahmad et al. [54], Ahmed et al. [27], Khanday & Sharma [55], and Kanmani et al. [56]. The functional groups were identified by means of FTIR spectroscopy [21]. The extraction of principal active compounds depends upon the solvent and type of plant part used. Solvents with high polarity yielded greater than those of low polarity solvents. Based on our results, ethanol yields a greater amount of plant extract, because of its high polarity. According to previous literature, ethanol produced a greater amount of extract from Melastoma malabathricum leaves as compared to other solvents [57]. Moreover, a study revealed a relatively high yield of C. sativa and C. colocynthis extract when ethanol was used as the solvent for extraction [58].

5. Conclusion

Based on results of this study, it is concluded that A. indica, C. colocynthis, E. globulus, C. sativa, N. tabacum, and P. hysterophorus had significant toxicity potential against the fall armyworm third instar larvae. GC-MS analysis demonstrated the presence of valuable bioactive compounds responsible for S. frugiperda mortality. As indicated by previous studies, an increase in the use of synthetic insecticides has led to the development of insect pest resistance and is especially harmful to the environment and beneficial organisms. Farmers should employ these kind of environmental friendly insecticides to lessen the impact of fall armyworm because these products are cheaper to use and better for the economy and the environment. These botanical extracts may be used by the farmers in both forms (crude extract or methanolic/ethanolic extracts) to minimize the damage of insect pests. However, more research is needed to purify the key molecules responsible for the mortality of fall armyworm and to determine the efficacy of these active compounds against the other insect pests.

CRediT authorship contribution statement

Usama Saleem: Writing – original draft, Methodology, Investigation, Formal analysis, Data curation. Muhammad Asrar: Supervision. Farhat Jabeen: Writing – review & editing. Syed Makhdoom Hussain: Writing – review & editing, Visualization. Dilbar Hussain: Validation, Supervision, Software.

Data availability

All the relevant data will be available on a reasonable request from corresponding author.

Funding

This research did not receive any funding from public, commercial, or non-profit organizations.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.