Organisms are always confronted with multiple stressors simultaneously. Combinations of stressors, rather than single stressor, may be more appropriate in evaluating the stress they experience. N. barkeri is one of predatory mite species that are commercialized for controlling spider mites. However, their biological control efficiency was often reduced because of high temperature and desiccation in summer. To understand how to improve the tolerance of N. barkeri to combined heat and desiccation stress, we pre-exposed the adult female of N. barkeri to high temperature, desiccation and high temperature × desiccation stress for acclimation. After proper recovery time, mites were subjected to high temperature × desiccation stress again to detect the acclimation effects. The results are as follows: (1) No decrease in mortality rate were observed under high temperature × desiccation stress after heat acclimation. Instead, it increased significantly with acclimation temperature and time. (2) Dehydration acclimation both at 25 °C and high temperatures reduced mortality rate under high temperature × desiccation stress. Mortality rate was only significantly correlated with the amount of water loss, but not with temperature or water loss rate in acclimation, suggesting the increased tolerance is related to dehydration stress rather than heat stress. Among all acclimations, chronic dehydration at 25 °C, 50% relative humidity were the most effective treatment. This study indicated dehydration acclimation is effective to enhance tolerance of N. barkeri to combined heat and desiccation stress, which can improve the efficiency of biological control under multiple stressors.

The flavor variation among different tea plant cultivars significantly influences their economic value. ‘Huangjinya’ (HJY), a typical light-sensitive etiolated tea cultivar, is prized for its fresh and mellow taste with low bitterness and astringency, and commands a high market value, serving as excellent germplasm for breeding superior-flavor tea varieties. Previous studies have largely focused on the mechanisms underlying fresh and umami tastes, whereas the regulatory mechanisms underlying bitterness and astringency remain poorly understood. In this study, two tea plant (Camellia sinensis (L.) O. Kuntze) cultivars with distinct bitterness and astringency phenotypes, namely ‘Fuxuan 9’ (FX) and HJY, were used to investigate the formation mechanism of reduced bitterness and astringency through integrated metabolomic and transcriptomic analyses. Metabolomic profiling identified 601 differentially accumulated metabolites between the two cultivars, which were significantly enriched in the flavonoid biosynthesis pathway. Notably, although the total flavonoid content was higher in HJY, the accumulation of non-esterified catechins (C, EC, EGC), which are key contributors to bitterness, was significantly lower than in FX. By contrast, the levels of esterified catechins (EGCG, GCG) showed no marked differences between cultivars. This distinct accumulation pattern provides a metabolic basis potentially associated with the reduced bitterness and astringency in HJY. Transcriptomic analysis revealed that the catechin biosynthetic gene CsLAR was significantly down-regulated in HJY, consistent with the reduced accumulation of non-esterified catechins. Promoter cloning and functional validation confirmed that the CsLAR promoters in both cultivars were active, which differed by only one regulatory element. Under shading treatment, CsLAR expression in HJY was more sensitive to light and decreased more markedly, suggesting that the expression of CsLAR may be regulated by transcription factors. Furthermore, 385 differentially expressed transcription factors were identified, with predicted binding sites in the CsLAR promoter region, implying their potential involvement in modulating catechin accumulation through modulation of CsLAR expression. Together, these multi-omics findings reveal molecular features potentially contributing to the low bitterness and astringency of HJY, providing a theoretical basis and candidate regulators for breeding tea cultivars with improved flavor profiles.