Novel methyl salicylate derivatives containing nerol and citronellol moieties for improved Acyrthosiphon pisum management

BACKGROUND Aphids have primarily been controlled by traditional chemical insecticides over the past decades, leading to health risks for honey bees. By contrast, plant volatiles such as methyl salicylate (MeSA) can not only repel aphids, but also attract their natural enemies, while being safe for bees, thus showing a promising prospect in aphid management. Our research group has previously discovered more active compounds for aphid management based on MeSA. Therefore, further structural optimization with MeSA as the lead compound is worth investigating. RESULTS Through the structural combination of nerol or citronellol with MeSA, two classes of derivatives were synthesized. The citronellol derivatives ( 6a – 6q ) exhibited superior binding affinities with Acyrthosiphon pisum OBP9 and better repelling activity against A. pisum than the nerol derivatives ( 4a – 4q ), among which 6d showed the strongest repellent activity, with a repellent proportion of 60.9%. Bearing binding constant ranged from 0.31 to 3.79 μ M , both citronellol and nerol derivatives had good binding affinity to Harmonia axyridis OBP15. Moreover, the derivatives 6d and 6h showed better attractive activities to male H. axyridis (choice rate: 63.9% and 67.2%) than the lead MeSA (63.3%). Mechanism study revealed that the citronellol derivatives owning the saturated conformation to offer increased flexibility exhibited superior bioactivity compared to the nerol derivatives with the cis conformation. Besides, 6d has low toxicity to honeybees ( Apis mellifera ). CONCLUSION The citronellol derivative 6d exhibited both aphid‐repelling activity and ladybug‐attracting activity, while being friendly to bees. 6d can be considered as a novel aphid control agent for aphid control in sustainable agriculture.