The management of insect pests and fungal diseases that cause damage to crops has become challenging due to the rise of pesticide and fungicide resistance. The recent developments in studies related to plant-derived essential oil products has led to the discovery of a range of phytochemicals with the potential to combat pesticide and fungicide resistance. This review paper summarizes and interprets the findings of experimental work based on plant-based essential oils in combination with existing pesticidal and fungicidal agents and novel bioactive natural and synthetic molecules against the insect pests and fungi responsible for the damage of crops. The insect mortality rate and fractional inhibitory concentration were used to evaluate the insecticidal and fungicidal activities of essential oil synergists against crop-associated pests. A number of studies have revealed that plant-derived essential oils are capable of enhancing the insect mortality rate and reducing the minimum inhibitory concentration of commercially available pesticides, fungicides and other bioactive molecules. Considering these facts, plant-derived essential oils represent a valuable and novel source of bioactive compounds with potent synergism to modulate crop-associated insect pests and phytopathogenic fungi.

Bioassay guided fractionation of an ethanol extract of leaves ofCanarium patentinerviumMiq. (Burseraceae Kunth.) led to the isolation of scopoletin. The structure of this coumarin was elucidated based on spectroscopic methods including nuclear magnetic resonance (NMR-1D and 2D) and mass spectrometry. Scopoletin inhibited the enzymatic activity of 5-lipoxygenase and acetyl cholinesterase with an IC₅₀equal to1.76±0.01 μM and0.27±0.02 mM, respectively, and confronted oxidation in the ABTS, DPPH, FRAP, andβ-carotene bleaching assay with EC₅₀values equal to5.62±0.03 μM,0.19±0.01 mM,0.25±0.03 mM and0.65±0.07 mM, respectively. Given the aforementioned evidence, it is tempting to speculate that scopoletin represents an exciting scaffold from which to develop leads for treatment of neurodegenerative diseases.