Chemical triggers that make plants defend themselves against insects could replace pesticides, according to a new paper in Bioorganic&Medicinal Chemistry Letters which identifies five chemicals that trigger rice plants to fend off a common pest - the white-backed planthopper, Sogatella furcifera

Pesticides are used around the world to control insects that destroy crops but their use has been criticized by activists groups, with the claim that some kill indiscriminately. For rice plants, this means pesticides kill the natural enemies of one of their biggest pests, the white-backed planthopper Sogatella furcifera. This pest attacks rice, leading to yellowing or "hopper burn," which causes the plants to wilt and can damage the grains. It also transmits a virus disease called, southern rice black-streaked dwarf virus, which stunts the plants' growth and stops them from "heading," which is when pollination occurs.

Left untreated, many of the insects' eggs would be eaten, but when pesticides are used these hatch, leading to even more insects on the plants. What's more, in some areas as many as a third of the planthoppers are resistant to pesticides.

Biology has long promised to usher in new solutions to help protect rice plants from infestation, though activist groups are as opposed to biology as they are chemistry. Regardless, progress continues and since plants have natural self-defense mechanisms that kick in when they are infested with pests like the planthopper, switching on that defense mechanism using chemicals that are not toxic to the insects or their natural enemies is a key topic.

In the new study, researchers developed a new way of identifying these chemicals. Using a specially designed screening system, they determined to what extent different chemicals switched on the plants' defense mechanism. The team designed and synthesized 29 phenoxyalkanoic acid derivatives. Of these, they identified five that could be effective at triggering the rice plants to defend themselves.

The researchers used bioassays to show that these chemicals could trigger the plant defense mechanism and repel the white-backed planthopper. This suggests that these chemicals have the potential to be used in insect pest management.

The next step for the research will be to explore how effective the chemicals are at boosting the plants' defenses and controlling planthoppers in the field.