Structure-activity relationships of pheromonostasis induced by ACCase-inhibitor herbicides in the moth Helicoverpa armigera

Many moth sex pheromone blends are derived from fatty acids and their production is regulated by a Pheromone Biosynthesis Activating Neuropeptide (PBAN). In prior work we showed that the herbicide Diclofop-acid, an acetyl-coenzyme A carboxylase (ACCase) inhibitor, inhibits PBAN-induced sex pheromone production in vitro. In this work we extend our study showing that several other herbicides, belonging to the 2-aryloxyphenoxypropionate ('FOP') and the cyclohexandione-oxime ('DIM') families significantly inhibit pheromone production by adult females whilst survival is unaffected by treatment. Enzyme activity in vitro and kinetic analysis revealed a K_m of 0.35 μM with K_i values of 0.1 and 0.28 μM due to Tralkoxydim and Diclofop inhibition, respectively. Inhibitory activity on PBAN-induced pheromone production by all herbicides tested revealed a potency order: Tralkoxydim > Clodinafop > Cycloxidim > Haloxyfop > Diclofop > Fenoxaprop > Fluazifop > Quizalofop, Quizalofop being inactive. Differences in inhibition efficiencies may be attributed to different binding sites on the enzyme or to the polarity and solubility of these compounds.