Illustration showing geraniol's repellant activity towards shoot and fruit borer moths. Credit: Rituparna Ghosh and Sagar Pandit

Scientists have identified a natural compound in a Himalayan eggplant variety that can prevent infestation by the shoot and fruit borer moth, a pest resistant to multiple insecticides1. Geraniol deters female moths from laying eggs on eggplant crops.

Eggplant (Solanum melongena) is the third most consumed solanaceous vegetable in India after potato and tomato. Shoot and fruit borer moth (Leucinodes orbonalis) attacks can cause 45-100% crop yield loss.

The caterpillars tunnel into tender shoots and fruits and lie hidden. Farmers apply a mix of synthetic pesticides in high doses and frequencies to eliminate the moths. Long term pesticide use has made the insects resistant to these chemicals. Eggplants in the market retain pesticide residue levels harmful for consumers.

To reduce the load of synthetic pesticides, scientists at the Indian Institute of Science Education and Research in Pune used metabolomics. Sagar Pandit and colleagues extracted leaf aromas from seven eggplant varieties, including the Himalayan eggplant (RL22) and applied the odours to separate filter papers.

The moths did not land on the RL22 filter paper but laid eggs on the other six. Gas chromatography and mass spectrometry helped pinpoint geraniol as the deterrent.

“The moths laid less than 10 eggs per plant after geraniol application, where they were laying 100 eggs earlier,” says co-author Sagar Pandit.The moths flew away from the geraniol-laced plants.

The researchers say geraniol-emitting devices might reduce pest infestations if installed in eggplant farms. High geraniol-emitting varieties of eggplant could also be another research prospect.