Gibberellin-Induced Early Flowering of Cnidium monnieri Advances the Arrival of Natural Enemies and Increases Their Abundance in Wheat Fields

Cnidium monnieri (L.) Cusson (Apiaceae) is a well-known insectary plant in farmlands. Its vegetative and flowering stages can promote the migration of natural enemies. However, the arrival of natural enemies in crop fields often lags behind the establishment of pest populations. As gibberellin can accelerate plant growth and flowering, we investigated whether gibberellin treatment could advance the recruitment of natural enemies by altering the phenology of C. monnieri. Field experiments were conducted in 2021 and 2022 to evaluate the effects of different gibberellin concentrations on plant phenology, growth traits, and natural-enemy abundance. For field validation, C. monnieri strips established in wheat fields were treated with water or 50 mg/L gibberellin. The 50 mg/L treatment advanced the onset of flowering by 21 days and the first detection of natural enemies on C. monnieri by 14 days in 2021 and 20 days in 2022. It also significantly increased natural-enemy abundance on C. monnieri in 2022. In wheat fields, the same treatment resulted in earlier detection and significantly greater abundance of natural enemies in 2022. The earlier detection of natural enemies was temporally consistent with the advancement of flowering. These findings indicate that manipulating the flowering phenology of insectary plants may improve the timing of natural-enemy establishment and strengthen conservation biological control.