Climate change leads to more frequent droughts that may alter multitrophic networks in agroecosystems by changing bottom-up and top-down effects on herbivorous insects. Yet, how bottom-up effects of drought alter tritrophic interactions remains poorly understood. This study investigated two intensities of drought stress in the tritrophic system consisting of sugar beet (Beta vulgaris), an aphid (Aphis fabae), and its parasitoid (Aphidius colemani). We thoroughly investigated each trophic level, examining the performance of plants, pest insects, and parasitoids, as well as the attraction of parasitoids to herbivore-induced plant volatiles (HIPVs). Drought stress negatively affected plant growth but benefited A. fabae, leading to faster development and a higher reproduction rate. Drought-stressed plants also emitted less plant volatiles, which resulted in reduced attraction of A. colemani to aphid-infested plants. Drought indirectly affected parasitoid performance, as evidenced by lower emergence rates and production of fewer females, although mummification rates were higher on drought-stressed plants. Reduced parasitoid attraction and performance on drought-stressed plants may exert lower top-down pressure on aphid populations. Combined with increased aphid performance, this may facilitate aphid outbreaks, which could further weaken drought-stressed plants. Our findings highlight the need to study multiple trophic levels and emphasize the importance of incorporating HIPVs and parasitoid attraction when assessing combined abiotic and biotic stresses in crops.

气候变化导致更频繁的干旱，可能会通过改变对草食昆虫的自下而上和自上而下的影响来改变农业生态系统的多营养网络。然而，干旱的自下而上影响如何改变三营养相互作用仍然知之甚少。本研究调查了由甜菜 (Beta vulgaris)、蚜虫 (Aphis fabae) 及其寄生蜂 (Aphidius colemani) 组成的三营养系统中的两种干旱胁迫强度。我们彻底调查了每个营养级，检查了植物、害虫和拟寄生物的表现，以及拟寄生物对食草动物诱导的植物挥发物（HIPV）的吸引力。干旱胁迫对植物生长产生负面影响，但有利于蚕豆，导致更快的发育和更高的繁殖率。干旱胁迫下的植物释放的植物挥发物也较少，这导致了 A. colemani 对蚜虫侵染植物的吸引力降低。干旱间接影响了寄生蜂的表现，表现在出苗率较低和雌性产量较少，尽管干旱胁迫植物的木乃伊化率较高。干旱胁迫植物上寄生蜂吸引力和性能的降低可能会对蚜虫种群产生较低的自上而下的压力。再加上蚜虫表现的增强，这可能会促进蚜虫的爆发，从而进一步削弱干旱胁迫下的植物。我们的研究结果强调了研究多个营养级的必要性，并强调了在评估作物非生物和生物胁迫组合时将 HIPV 和拟寄生物吸引力纳入其中的重要性。