Chitosan-cellulose nanoencapsulation systems for enhancing the insecticidal activity of citronella essential oil against the cotton leafworm Spodoptera littoralis

Essential oils of plant origin could provide green and effective alternative to synthetic insecticides. To avoid the instability and high volatility of essential oils, it is necessary to introduce new techniques to protect their bioactive constituents. In the current study, nanoencapsulation systems from chitosan nanoparticles (CSNPs) and cellulose nanofibers (CNF) were used to control the release of citronella essential oil (CEO) for use against cotton leafworm, Spodoptera littoralis (Boisd.). The size, entrapment efficiency, and kinetic of CEO release from CSNPs and CSNPs/CNF nano-systems were studied. The size of CSNPs was increased from 102.1 +/- 0.55 nm to 171.9 +/- 2.4 nm and 426.9 +/- 4.38 nm due to addition of CEO and CEO/CNF, respectively, whereas the encapsulation efficiency of CEO was 61.8 +/- 1% and 90.8 +/- 1% for CSNPs and CSNPs/CNF systems, respectively. CEO release after two weeks was 100% and 74% from the CSNPs and CSNPs/CNF nano-systems, respectively, while the release of the control sample (non-encapsulated CEO) was 100% after only 6 h. Experiments on insecticidal activity revealed that all nano-formulations disrupted the development of S. littoralis. CEO-CSNPs/CNF was the most effective system; it significantly prolonged the larval and pupal durations compared to control group. A significant reduction in pupal weight, adult longevity, and female fecundity was observed particularly after CEOCSNPs/CNF and CEO-CSNPs treatments. The semi-field experiment revealed that CSNPs/CNF had the greatest persistence effect, resulting in the highest larval mortality across all tested intervals, followed by CEO-CSNPs and CEO-NE. CSNPs and CEO, on the other hand, demonstrated little or no persistence effects. The observed results revealed that CSNPs and CNF could improve the insecticidal effect of CEO as bio-insecticide against S. littoralis larvae.