Extraction, characterization and evaluation of the larvicidal, ovicidal and antifeedant effects of crude cashew nut shell liquid against spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae L.).

Spodoptera frugiperda (J.E. Smith), commonly known as the fall armyworm (FAW), is an invasive insect pest of maize and other economically important cultivated crops globally. In the absence of proper control methods, FAW has the potential to cause 21 to 50 percent of maize crop yield losses. Currently, synthetic insecticides are widely used in the management of FAW outbreaks around the world. Nonetheless, overdependence on
synthetic insecticides leads to undesirable environmental and human health issues. Botanical insecticides such as Cashew nut shell liquid (CNSL) have been shown to exhibit insecticidal properties against a broad spectrum of insect pests and are known to be less harmful to the environment and humans. Hence, this study evaluated the insecticidal properties of CNSL against FAW in order to assess its potential use as an alternative to synthetic insecticides. Crude CNSL was extracted from cashew nutshells (CNSs) by solvent extraction method. Phytochemical screening and Thin Layer Chromatography (TLC) were performed to qualitatively identify the secondary metabolites present in it. Additionally, Gas Chromatography-Mass Spectrometry (GC-MS), Fourier Transform Infrared spectroscopy (FTIR), and Ultraviolet-visible (UV-Vis) spectrometry techniques were used to characterize and quantify some of the identified compounds. Furthermore, bioassays such as topical and no-choice feeding assays were performed to evaluate the ovicidal, larvicidal, and antifeedant effects of crude CNSL against FAW. Phytochemical screening revealed the presence of various bioactive compounds including phenols, tannins, flavonoids, alkaloids, saponins, steroids, glycosides, and terpenoids. All the other characterization techniques; TLC, FTIR, and GC-MS revealed the presence of alkyl phenolic lipids such as cardol (5-pentadecyl resorcinol) and cardanol (3-pentadecyl
phenol). Literature showed that these alkyl phenolic compounds are the ones responsible for the biological activity of CNSL. The toxicity of CNSL against FAW larvae was dosedependent. The highest mortality of eggs (99.15 ± 0.0 %) and larvae (97.99 ± 0.0 %) were both recorded at 7.0 w/v %, respectively. The lethal concentrations LC50 (95 CI %) were 2.50 (0.22-4.05 w/v %), for egg and 1.92 (1.71-2.15 w/v %) for larval mortality,
respectively. The effective concentration (EC50) for the antifeedant effect was found to be 1.05 (0.81-1.29 w/v %). Results showed that CNSL has insecticidal properties and antifeedant effects against FAW. Hence, it can be exploited as a relatively cheap, safe, and eco-friendly alternative insecticide for managing FAW outbreaks in Zambia.

Keywords: Cashew, Fall armyworm, Spodoptera frugiperda, cashew nut shell liquid