Less is more for greener insecticide.

Romanelli, GP, EG Virla, PR Duchowicz, AL Gaddi, DM Ruiz, DO Bennardi, E del Valle Ortiz and JC Autino.  2010.  Sustainable synthesis of flavonoid derivatives, QSAR study and insecticidal activity against the fall armyworm, Spodoptera frugiperda (Lep.: Noctuidae). Journal of Agricultural and Food Chemistry 58:6290-6295.

Synopsis by Evan Beach
Aug 23, 2010

No solvent and no corrosive acids. That’s part of the recipe for a new, less polluting method of making chemicals that kill an important crop pest. Taking their inspiration from natural plant chemicals called flavones, the authors of the study developed a way to make, compare, and test the insecticides, and used the information to create a predictive computer model.

The cleaner synthesis was used to control fall armyworms, one of the main threats to corn crops in many parts of the world. The new method avoids toxic solvents and strong mineral acids that were needed in earlier processes.

Instead, it relies on a metal catalyst that works at low levels: one catalyst molecule per 200 molecules of starting material. The catalyst could be easily recovered at the end of the chemical reaction and recycled several times, reducing waste.

Flavones protect plants against a variety of bacteria and insects. Some flavones also show beneficial effects in humans as antioxidants, anti-inflammatory agents, antimicrobials and anticancer agents.

The researchers made synthetic flavones using the greener technique and found that the chemicals were effective against the armyworm larvae. Based on these results, the researchers then created a computer model to predict which natural flavones might be worth testing as pesticides. They analyzed the structures of more than a dozen plant flavones and found two with characteristics in common with the chemicals that worked against armyworms.

One of the natural flavones, luteolin, occurs naturally in the human diet, in carrots, peppers, celery, and some spices. The other, apigenin, is common in citrus fruit, tea, and a variety of vegetables. Both chemicals are often cited for their therapeutic effects in humans.

The next step is for scientists to test whether these two natural flavones do indeed kill insects, as predicted by the model. While the natural flavones would probably have minimal environmental impacts if applied as pesticides, the synthetic flavones reported in the study were not tested for environmental persistence or toxicity to organisms besides armyworms. Those experiments would confirm whether the greener preparation leads to greener pesticides.