Pests are one of farming’s biggest problems. For cabbage growers the main enemy is the cabbage aphid, which does serious damage to crops and costs farmers money.
Traditional control methods are losing their effect. Aphids are becoming resistant to synthetic insecticides, and agrochemicals harm the environment. Where aphids come from in a greenhouse, why pyrethroids barely touch them, and what ants have to do with it are covered in the wiki article on aphids under protected cultivation.
Researchers at the International Centre of Insect Physiology and Ecology (icipe) looked for a more sustainable solution based on a long-known effect: natural plant scents change how insects behave. There is even a farming method built on it, push-pull, which pairs crops with plants whose repellent properties keep pests away.
The researchers used an olfactometer, a device for studying how insects respond to different smells, to compare how attractive cabbage and rosemary volatiles were to aphids.
At first the aphids clearly preferred the smell of cabbage over rosemary and spent more time in the cabbage-scented part of the olfactometer. When the two scents were combined, cabbage attracted fewer aphids, which suggests that rosemary volatiles repel them. The aphids reacted negatively to linalool, α-terpineol and camphor in the rosemary scent.
Based on these results, the researchers concluded that rosemary grown alongside cabbage could act as a deterrent. Used as a “living shield,” it would help farmers rely less on chemical insecticides and lower both costs and environmental impact.
