Potential of Dittrichia viscosa as a biopesticide for controlling Bradysia sp. in nurseries of aromatic plants

Bradysia sp. (Diptera) or fungus gnats are among the most important pests affecting nursery root cuttings for plant multiplication, due to the direct feeding damage caused by their larvae. Currently, new solutions based on botanical and biological solutions are being studied and tested to address these pests. Dittrichia viscosa (Asteraceae), a shrub native to the Mediterranean region, has been identified as a potential botanical insecticide for controlling various pests.

In two separate trays, we installed cuttings from five aromatic semi-wood species (Rosmarinus officinalis with white flowers (RoW), R. officinalis with purple flowers (RoP), Santolina rosmarinifolia, Thymus vulgaris, and Lavandula angustifolia). A heavily infected plant with Bradysia sp. was placed nearby to infest plants. After infestation, every two weeks, an aqueous extract of D. viscosa with a concentration of 2% m/m was applied to one tray (treated modality), while the other tray served as the untreated control. A spraying irrigation system was used to enhance application efficiency. Using a Log-Rank test (Kaplan–Meir Survival), we evaluated i) the susceptibility of the plant species to the pest and ii) the effectiveness of the plant extract in reducing plant mortality.

Our findings confirmed our expectations, showing that T. vulgare was the least susceptible species to Bradysia sp., followed by RoP.

The application of D. viscosa extract reduced plant mortality by 20% in RoW and 5% in L. angustifolia.

Future trials must standardize the species tested as hosts and the concentration of the D. viscosa extract to ensure consistent results. Additionally, it will be crucial to analyse the specific compounds within the extract that may be responsible for its observed effects. Despite these considerations, the current findings suggest promising potential for using D. viscosa extract in sustainable pest management strategies.