Eucalyptus Globulus Essential Oil-Based Nanoemulsions: Comprehensive Development, In Vitro and In Silico Assessment Against Spodoptera Litura

Engineering Nanoscience Environmental Engineering Chemistry Bioengineering Environmental Chemistry Life Sciences
Eucalyptus globulus nanoemulsions Spodoptera litura ovicidal activity repellency molecular docking

Academic Background

With the rapid growth of the global population, which is expected to reach 9.7 billion by 2050, food security has become an increasingly pressing issue. Agricultural productivity is affected by various factors, with pest damage to crops being particularly severe. The tobacco cutworm (Spodoptera litura), a polyphagous pest widely distributed across the Asia-Pacific and Oceania regions, can infest 128 plant species, including economically important crops such as soybeans, cotton, peanuts, and tomatoes. For a long time, farmers have relied on synthetic chemical pesticides to control pests, but these pesticides have had negative impacts on non-target organisms, human health, and the environment. Additionally, the resistance of pests to multiple pesticides has been increasing. Therefore, there is an urgent need to develop environmentally friendly and sustainable alternatives. Plant-based pesticides, due to their low toxicity, rapid biodegradability, and minimal impact on natural enemies, are considered a strong alternative to synthetic chemical pesticides. In recent years, essential oil (EO)-based pesticides have gained significant attention due to their broad-spectrum efficacy and lower toxicity. However, the poor water solubility, high volatility, and sensitivity to light and oxygen of essential oils limit their direct application. Nanoemulsion technology, by encapsulating essential oils in nanoparticles, can effectively address these issues and enhance their bioactivity.

Source of the Paper

This paper was co-authored by Ankur, Nida, Narender Singh, Sanjiv Mullick, and Alka Gupta, who are affiliated with the University of Delhi and the Institute of Genomics and Integrative Biology (IGIB) under the Council of Scientific and Industrial Research (CSIR) in India. The study was accepted on March 21, 2025, and published in the journal Bionanoscience with the DOI 10.1007/s12668-025-01912-8.

Research Process and Results

1. Extraction and Composition Analysis of Eucalyptus globulus Essential Oil

The researchers obtained Eucalyptus globulus essential oil (EGeO) from the Nilgiris Eucalyptus Oil Distillery in Tamil Nadu, India, and analyzed its composition using gas chromatography-mass spectrometry (GC-MS). The results showed that the essential oil primarily consists of monoterpenes and sesquiterpenes, with 1,8-cineole (67.14%), α-pinene (7.50%), and α-terpineol (7.08%) being the major components.

2. Preparation and Optimization of Nanoemulsions

Using a low-energy spontaneous emulsification method, the researchers prepared oil-in-water (O/W) nanoemulsions by mixing 15% Eucalyptus globulus essential oil with 5% emulsifier (Tween 80 or Span 80). Characterization of the nanoemulsions using dynamic light scattering (DLS) and transmission electron microscopy (TEM) revealed that nanoemulsions prepared with Tween 80 had a smaller average droplet diameter (289.16 nm) and a lower polydispersity index (PDI < 0.3), indicating good monodispersity. In contrast, nanoemulsions prepared with Span 80 exhibited higher polydispersity.

3. Stability and Drug Loading Efficiency of Nanoemulsions

The researchers evaluated the long-term stability of the nanoemulsions and found that after 50 days of storage at 25°C and 5°C, the droplet diameter of nanoemulsions prepared with Tween 80 showed minimal changes, indicating good stability. Additionally, the drug loading efficiency of the nanoemulsions was as high as 97%, demonstrating effective encapsulation of Eucalyptus globulus essential oil.

4. Bioactivity Testing

The researchers conducted a series of biological experiments to evaluate the efficacy of Eucalyptus globulus essential oil nanoemulsions against Spodoptera litura. The results showed that the nanoemulsions exhibited significant ovicidal activity, with an LC50 value of 22.331 mg/mL. Furthermore, the nanoemulsions demonstrated significant repellent effects on neonate larvae, with larvae clearly avoiding the nanoemulsion-treated areas in glass tunnel olfactometer tests. In insecticidal experiments, the nanoemulsions significantly reduced larval survival, with a 10 mg/mL concentration resulting in 92% larval mortality.

5. Molecular Docking Studies

To further elucidate the insecticidal mechanism of Eucalyptus globulus essential oil, the researchers conducted molecular docking studies on seven major components of the essential oil. The results showed that these components had good binding affinity with the chemosensory proteins (CSPs) of Spodoptera litura, with binding energies ranging from -4.0 to -5.2 kcal/mol. This suggests that the components of Eucalyptus globulus essential oil may interfere with the olfactory system of pests by inhibiting CSP activity, thereby exerting repellent and insecticidal effects.

Research Conclusions and Significance

This study demonstrates that Eucalyptus globulus essential oil-based nanoemulsions exhibit significant ovicidal, repellent, and insecticidal activities against Spodoptera litura. The good stability and high drug loading efficiency of the nanoemulsions provide potential for their application in agriculture. Additionally, molecular docking studies reveal the interaction mechanisms between the components of Eucalyptus globulus essential oil and pest chemosensory proteins, offering a theoretical basis for the development of novel biopesticides.

Research Highlights

  1. Effective Control of *Spodoptera litura*: Eucalyptus globulus essential oil nanoemulsions exhibit significant ovicidal, repellent, and insecticidal activities under laboratory conditions, providing new insights for the integrated management of Spodoptera litura.
  2. Stability and High Drug Loading Efficiency of Nanoemulsions: Nanoemulsions prepared using the low-energy spontaneous emulsification method exhibit good stability and high drug loading efficiency, addressing the issues of poor water solubility and high volatility of essential oils.
  3. Molecular Mechanism Research: Molecular docking studies reveal the interaction mechanisms between Eucalyptus globulus essential oil components and pest chemosensory proteins, providing a scientific basis for the development of novel biopesticides.

Application Value

This study provides important references for the development of environmentally friendly biopesticides. Eucalyptus globulus essential oil nanoemulsions, as a green pesticide, have the potential to play a significant role in the integrated pest management of agricultural pests. Furthermore, this study offers technical support and theoretical guidance for the application of other plant essential oils in pest control.