Farmers are showing growing interest in oils extracted from herbs like thyme,rosemary and mint because of their capability of repelling, or even killing insects, Murray Isman, an entomologist at the University of British Columbia in Canada told National Geographic
The oils destroy insect nervous system, making their muscles extremely hyperactive, which eventually leads to fatal spasms. Also, they attack bugs' cell membranes, causing a death from leakage of body fluids. The latter, said Isman, is most effective against small, soft-bodied bugs like aphid and whiteflies as they are more vulnerable to "having their membranes melted."
These spices are already available wholesale for the food flavoring and perfume industries so the price is not the issue. However, since the oil-based pesticides evaporate quickly in the sun, farmers have to spray them every few days, rather than every few weeks as they used to do.