Bioactivity of Zanthoxylum armatum fruit extract against Spodoptera frugiperda and Tuta absoluta

Abstract

In Africa and Asia, fall armyworm (Spodoptera frugiperda) and South American tomato pinworm (Tuta absoluta) have become severe invasive pests of maize and tomato, respectively. They rapidly develop resistance to commercial pesticides. Therefore, there is an urge to integrate new eco-friendly pesticides into the management programs. Bamboo-leaf prickly ash, Zanthoxylum armatum (Za), is known to have insecticidal activities. We tested Za’s n-hexane extract against these two pests. Median lethal concentrations (LC50) at 96 h after treatment (HAT) against second-instar S. frugiperda and T. absoluta larvae were 4.41 and 4.42 mL/L, respectively. At ≥ 22.0 mL/L concentration, the extract showed a 100% ovicidal effect against both the pest species. LCQTOF analysis revealed that fatty acids constituted ~ 95% of this extract; carboxylic acids and secondary metabolites such as alkaloids and flavonoids accounted for the remaining portion. Extract’s foliar application also showed oviposition deterrence against these two pests. At ≥ 22.0 mL/L extract concentration, no S. frugiperda oviposition was observed. At ≥ 6.0 mL/L, extract reduced the T. absoluta oviposition by > six folds. To understand the basis of this deterrence, we conducted Za extract’s GCMS analysis. It revealed that monoterpenes, sesquiterpenes, and their derivatives were the most abundant constituents (55%), followed by fatty acids and their derivatives (34%), and aromatic compounds (10%). We infer that this extract is a unique combination of antibiosis- and antixenosis-causing, shelf life-increasing, and activity-enhancing compounds. It can be a highly useful biopesticide for integrating into the S. frugiperda and T. absoluta management programs.