Phenolic compounds as controllers of Sitophilus zeamais: A look at the structure-activity relationship

There are many species of insects that feed, live, and reproduce in stored food around the world, producing significant economic losses. One of the most damaging insects to stored maize grains is Sitophilus zeamais. For many years, insect pest control in the Argentine grain postharvest system was accomplished through the use of dichlorvos (DDVP). The high concentrations used resulted in the rejection of the product and a risk to human and environmental health. An environmentally friendly alternative to the use of synthetic pesticides is the application of essential oils or their main constituents. This work evaluated the effects of ten phenolic compounds as bio-insecticides or repellents against Sitophilus zeamais. The repellent and toxic effects were determined by a two-way olfactometer test and a contact bioassay, respectively. Also, the acetylcholinesterase (AChE) activity was calculated. A structure-activity relationship was performed using the molecular parameters and the results of bioassays. In this study, we found that carvacrol (LC50 = 221 mu mol/cm2) and thymol (LC50 = 196 mu mol/cm2) have insecticidal effects against S. zeamais and they presented high inhibition of AChE with IC50 values of 0.019 and 0.96 mM, respectively. Besides, thymol caused the highest repellency (63% at 40 mu M). The structural-activity analysis reveals that the hydroxyl group is important for the insecticidal properties and that the aromatic ring and its substituent have effects on its efficacy as bioinsecticides. The present study contributes to the rational design of pesticides derived from natural compounds.