Antifeedant and feeding deterrent activity of Sphaeranthus indicus Leaf extract against Achaea janata (Lepidoptera: Noctuidae)

Introduction

The semilooper, Achaea janata L., is a serious defoliator of Gmelina arborea and several other host plants, causing considerable yield losses. Management of this pest largely depends on synthetic insecticides, which often lead to problems such as pesticide resistance, environmental contamination and adverse effects on non-target organisms. In recent years, botanical insecticides have gained importance due to their biodegradability, safety and compatibility with integrated pest management (IPM) programmes. Sphaeranthus indicus Linn., a medicinal plant widely distributed in India, is known to possess diverse bioactive compounds with insecticidal, antifeedant and growth regulatory properties. However, systematic studies on its feeding deterrent effects against A. janata are limited. The present study was therefore undertaken to assess the antifeedant activity of S. indicus leaf extracts at different concentrations and to compare their efficacy with neembased and chemical insecticides.

Methods and Materials

Larvae of Achaea janata were collected from Gmelina arborea fields and reared under laboratory conditions at room temperature. Healthy and uniformly grown larvae were used for the bioassay. Fresh leaves of Sphaeranthus indicus were collected, shade-dried and powdered. The powdered material was subjected to Soxhlet extraction using a suitable organic solvent. The extraction was continued until the solvent in the siphon tube became colourless. The extract was concentrated by evaporating the solvent under reduced pressure and stored at 4 °C. Required concentrations (0.25, 0.50, 0.75 and 1.0%) were prepared using distilled water with a suitable emulsifier. The treatments consisted of S. indicus extract at four concentrations (0.25, 0.50, 0.75 and 1.0%), Nimbecidine (0.5%), Profenophos (0.05%) and an untreated control. Fresh castor leaves were weighed and treated with respective concentrations. After air drying, treated leaves were offered to individual larvae. After 24 hours, the weight of leaf material consumed, uneaten leaf and faecal pellets excreted were recorded. The experiment was conducted in a completely randomized design and data were subjected to statistical analysis.

Results and Discussion

The results revealed significant differences in leaf consumption among treatments. Larvae consumed the least quantity of leaf material in Profenophos treatment (0.979 g), followed by Nimbecidine (1.661 g) and S. indicus at 1.0% concentration (2.201 g). In contrast, the maximum consumption was observed in the untreated control (5.288 g) (Table 1). A gradual decrease in feeding was noticed with increasing concentrations of S. indicus, clearly indicating dose-dependent antifeedant activity. The quantity of uneaten leaf material differed significantly among the various treatments, clearly reflecting the feeding deterrent effect of the test substances. Maximum uneaten leaf was recorded in the Profenophos treatment (5.381 g), indicating the strongest suppression of feeding activity, followed by the neem-based formulation Nimbecidine (4.707 g) and Sphaeranthus indicus at 1.0% concentration (4.181 g). In contrast, the untreated control recorded the least quantity of uneaten leaf (1.085 g), confirming unrestricted and normal feeding behaviour in the absence of deterrent compounds. Similar reductions in feeding and increased leaf rejection due to antifeedant compounds have been reported earlier for several botanical extracts (Isman, 2006; Koul et al., 2008; Pavela, 2016) [1,3,4] . The gradual increase in uneaten leaf with increasing concentrations of S. indicus suggests a clear dose-dependent antifeedant response, which is characteristic of many plant-derived secondary metabolites (Warthen and Morgan, 1990) [7] . Significant variation was also observed in the quantity of faecal pellets excreted by Achaea janata larvae under different treatments. Higher faecal pellet production was recorded in larvae fed on Nimbecidine-treated leaves (2.182 g) and S. indicus at 1.0% concentration (1.783 g) compared to lower concentrations and the untreated control. Increased faecal excretion may indicate physiological or biochemical disturbances in the larval gut caused by bioactive compounds, leading to reduced digestive efficiency and poor nutrient assimilation. Similar effects of neem and other botanical extracts on gut physiology, digestion and metabolism in lepidopteran larvae have been reported by Senthil-Nathan (2013) [6] and Jeyasankar et al. (2012) [2] . Based on leaf consumption data, the descending order of antifeedant activity was Profenophos > Nimbecidine > S. indicus 1.0% > 0.75% > 0.50% > 0.25% > untreated control. Although Profenophos and Nimbecidine showed superior feeding deterrence, the efficacy of S. indicus, particularly at higher concentrations, was noteworthy and comparable to neem-based formulations. Botanical antifeedants are known to deter feeding by affecting chemoreceptors and disrupting normal feeding behaviour (Saxena, 1989; Isman, 2006) [5,1] . The strong antifeedant activity exhibited by S. indicus at 1.0% concentration highlights its potential as an ecofriendly and sustainable alternative to synthetic insecticides for the management of A. janata, especially within integrated pest management programmes.

Conclusion

The study highlights the potential of Sphaeranthus indicus leaf extracts as an effective antifeedant against Achaea janata. Its dose-dependent feeding deterrence and physiological effects on larvae suggest its suitability for incorporation into eco-friendly pest management strategies.

Disclaimer

(Artificial intelligence) Author(s) hereby declare that no generative AI technologies such as Large Language Models (Chat GPT, COPILOT, etc) and text-to-image generators have been used by them during writing or editing manuscripts.

Acknowledgement

AcknowledgementsThe Author(s) express their sincere gratitude to the CAMPA (MoEF) for financial support, Director General, ICFRE, Dehradun, the Director, and the Group Coordinator of Research (GCR) of the Institute for their constant support, encouragement and guidance in experimenting. Competing Interests Author(s) declared that no conflict of interests exists.

References

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