Fusarium avenaceum is distributed worldwide and directly causes considerable crop losses. The compositions of lemongrass essential oils (EOs) were analysed by gas chromatography-mass spectrometry (GC-MS). The antifungal activity of lemongrass essential oils (EOs) and the main compounds against F. avenaceum were evaluated in vitro, and the underlying mechanism was investigated. Geranial, geranyl acetate, β-citronellol, citronellal, limonene, and citral were demonstrated to be the major constituents of the EOs. Lemongrass EOs and the main compounds possessed the antifungal effect against F. avenaceum, and citral exerted the strongest antifungal effects against F. avenaceum compared with other compounds, with IC₅₀ values of 0.087 µl/mL. Lemongrass EOs and their major constituents increased the permeability of the F. avenaceum plasma membrane, resulting in increased conductivity, protein and soluble sugar leakage. The activity of pectin methyl galacturonase (PMG) in F. avenaceum was suppressed after treatment with lemongrass EOs. The results indicated that lemongrass EOs inhibited F. avenaceum growth by targeting its plasma membrane and reduced its pathogenicity by inhibiting enzyme activity.

The tea mosquito bug, Helopeltis theivora Waterhouse, (Hemiptera: Miridae) is a significant sap-sucking pest in tropical tea plantations that causes substantial losses in tea production on Hainan Island, China. The morphological and ultrastructural characteristics of H. theivora antennae have not been elucidated. Here, we used several microscopy techniques (SDM, SEM, and TEM) to investigate the morphology as well as the setae and sensilla on the antennae of nymphs and adults of H. theivora. SDM observations indicated that the antennae of H. theivora were filamentous in shape and included four segments: scape, pedicel, flagellum I, and flagellum II. The length of the antenna was approximately twice that of the body and the setae were enriched in flagellum II. The SEM results showed that there were a total of six types of sensilla on the antenna of H. theivora, including the sensilla chaetica (SCh), sensilla trichoidea (ST), sensilla basiconica (SB), sensilla coeloconica (SCo), sensilla mammilliformia (SM), and Böhm’s bristles (BB). In particular, there were three subtypes (I, II, and III) of different lengths in SCh and SB, and two subtypes of straight (I) and curved (II) sensilla in ST. The TEM results indicated that diverse internal structures were present in SCh, ST, SB, and SCo, suggesting different functions and different sensory mechanisms of these four main sensilla in the orientation behavior of H. theivora on tea plants. These findings provide a theoretical basis for further exploration of the olfactory orientation of H. theivora in tropical tea plantations and pave the way for the development of semiochemical-based control options in the future.