Terpenes and phenolics in alcoholic extracts of pine needles exhibit biocontrol of weeds (Melilotus albus and Asphodelus tenuifolius) and insect-pest (Plutella xylostella)

Abstract

Massive use of synthetic chemicals exerts deleterious effects on human and environmental health, which calls for the development of novel alternatives to manage agricultural pests. Botanical pesticides have drawn great interest due to their non-toxic and eco-friendly nature. Therefore, under this study, leaf-needles of chir pine (Pinus roxburghii) were extracted by different solvents to obtain effective biochemical. These extracts were evaluated for biocontrol of two weed and an insect-pest species. Pine needles were soaked separately in methanol, ethanol, hot and cold water in the volume to weight ratio of 5:1 (solvent:pine needles) for 7 days. Extraction yield, and contents of organic acids, siloxanes and amides were higher with hot and cold water, while alcohols, ketones, terpenes and phenolic compounds were greater in methanolic and ethanolic extracts. These biochemicals with respective extractants increased quantitatively and progressively but not beyond 7 days. Raw extracts (with variable dilution) were employed topically against two weed species (Melilotus albus and Asphodelus tenuifolius) and an insect-pest (Plutella xylostella L.). Greater weed biocontrol efficacy through soaking of M. albus and A. tenuifolius weed seeds was exhibited by methanolic extract (100% concentration) with the highest germination inhibition (74% and 65%) followed by ethanolic extract (68% and 64%), respectively. The highest mortality (92%) of P. xylostella insects was achieved through methanolic extract bath (20% concentration) after 120 h. These results conclude that alcoholic extracts of pine needle contain more effective biochemicals (e.g., phenols and terpenes) with bio-pesticidal characteristics as compared to that from aqueous extracts. Therefore, the alcoholic extracts bear great potential to develop the bio-pesticides as novel and safe alternatives for weeds as well as insect-pest management.