Plants employ abundant toxic secondary metabolites to
withstand
insect attack, while pollinators can tolerate some natural defensive
compounds. Coumarins, as promising green alternatives to chemical
insecticides, possess wide application prospects in the crop protection
field. Herein, the bioactivities of 30 natural coumarin derivatives
against Aphis gossypii were assessed and revealed
that 6-methylcoumarin exhibited potent aphicidal activity against
aphids but displayed no toxicity to honeybees. Additionally, using
biochemical, bioinformatic, and molecular assays, we confirmed that
the action mode of 6-methylcoumarin against aphids was by inhibiting
acetylcholinesterase (AChE). Meanwhile, functional assays revealed
that the difference in action site, which located in Lys585 in aphid
AChE (equivalent to Val548 in honeybee AChE), was the principal reason
for 6-methylcoumarin being toxic to aphids but safe to pollinators.
This action site was further validated by mutagenesis data, which
uncovered how 6-methylcoumarin was unique selective to the aphid over
honeybee or mammalian AChE. Furthermore, a 2D-QSAR model was established,
revealing that the central structural feature was H3m, which offers
guidance for the future design of more potent coumarin compounds.
This work provides a sustainable strategy to take advantage of coumarin
analogues for pest management while protecting nontarget pollinators.