Volatiles emission of crucifers (Brassicaceae) under drougth stress and attraction of natural enemy Trichogramma pretiosum Riley, 1879 (HYM.: Trichogrammatidae)

Abiotic stressors play a central role in shaping plant–insect interactions through their effects on plant physiology and chemical signaling. Among these factors, water deficit represents a major driver of changes in plant metabolism, with cascading effects on herbivores and their interactions with natural enemies. Although changes in precipitation patterns are expected to increase the frequency of drought events in several regions, water deficit itself can independently modulate tritrophic interactions. The effects of reduced water availability were investigated in three Brassica oleracea varieties (kale—B. oleracea var. acephala cv. Manteiga HS-20; broccoli—B. oleracea var. italica cv. Piracicaba; and cabbage—B. oleracea var. capitata cv. Bobcat), as well as its consequences for the specialist herbivore Plutella xylostella, a key pest of Brassicaceae crops, and the egg parasitoid Trichogramma pretiosum, a natural enemy associated with this species. Plants were subjected to two soil water regimes (50% and 100% of field capacity), in which reduced water availability was used to simulate water deficit conditions, and the resulting effects on plant chemical composition and volatile emissions were assessed. The effects of plant-mediated changes on oviposition behavior of P. xylostella and on the olfactory responses of T. pretiosum were evaluated using greenhouse and laboratory assays. Water deficit significantly altered plant volatile profiles. Oviposition responses of P. xylostella varied among host plants, with a preference for well-watered plants in kale, increased oviposition on water-deficit plants in cabbage, and no significant preference in broccoli. In contrast, T. pretiosum consistently exhibited greater attraction to volatiles emitted by plants under reduced water availability. These results indicate that water deficit indirectly influences herbivore and parasitoid behavior through plant-mediated changes in volatile emissions, with potential implications for pest management under water-limited conditions.