Aphidius gifuensis is the dominant parasitic natural enemy of aphids. Elucidating the molecular mechanism of host recognition of A. gifuensis would improve its biological control effect. Chemosensory proteins (CSPs) play a crucial role in insect olfactory systems and are mainly involved in host localization. In this study, a total of nine CSPs of A. gifuensis with complete open reading frames were identified based on antennal transcriptome data. Phylogenetic analysis revealed that AgifCSPs were mainly clustered into three subgroups (AgifCSP1/2/7/8, AgifCSP3/9, and AgifCSP4/5/6). AgifCSP2/5 showed high expression in the antennae of both sexes. Moreover, AgifCSP5 was found to be specifically expressed in the antennae. In addition, fluorescent binding assays revealed that AifCSP5 had greater affinities for 7 of 32 volatile odor molecules from various sources. Molecular docking and site-directed mutagenesis results revealed that the residue at which AgifCSP5 binds to these seven plant volatiles is Tyr75. Behavior tests further confirmed that trans-2-nonenal, one of the seven active volatiles in the ligand binding test, significantly attracted female adults at a relatively low concentration of 10 mg/mL. In conclusion, AgifCSP5 may be involved in locating aphid-infested crops from long distances by detecting and binding trans-2-nonenal. These findings provide a theoretical foundation for further understanding the olfactory recognition mechanisms and indirect aphid localization behavior of A. gifuensis from long distances by first identifying the host plant of aphids.

The compound N-(5-(4-chlorobenzyl)-1,3,5-triazinan-2-ylidene)nitramide (C₁₀H₁₂ClN₅O₂, M = 269.70) was synthesized and structurally confirmed by ¹H NMR, ¹³C NMR, HRMS and single-crystal x-ray diffraction. The crystal belongs to the monoclinic system with space group P2₁/c. The title compound consisted of a benzene ring and a 1,3,5-triazine ring. All carbon atoms in the benzene ring were nearly coplanar with a dihedral (C6–C5–C10 and C7–C8–C9) angle of 1.71°and all non-hydrogen atoms of the 1,3,5-triazine ring were not planar, but exhibited a half-chair conformation. The crystal structure was stabilized by a strong intramolecular hydrogen bonding interaction N(3)–H(3)···O(2) and three intermolecular hydrogen bonding interactions, N(2)–H(2)···O(1), N(2)–H(2)···N(4) and N(3)–H(3)···Cl(1). The preliminary bioassay showed that the title compound showed not only aphicidal activity against Sitobion miscanthi (inhibition rate: 74.1%) and Schizaphis graminum (77.5%), but also antifungal activities against Pythium aphanidermatum (62.0%). These results provide valuable guidelines for the design and synthesis of novel aphid control agents and fungicides.

Semiaphis heraclei Takahashi (Hemiptera: Aphididae) serves as a vital resource for natural enemies from functional plant Cnidium monnieri (L.) Cusson (Apiaceae), playing a crucial role in ecological dynamics. Endosymbionts influence the performance of their hosts. Here, we determined the communities of facultative endosymbionts in aphids from Lonicera japonica Thunb. (Caprifoliaceae), Apium graveolens L. (Apiaceae), and C. monnieri and assessed the performance of four aphid clones. The infection rates of Serratia symbiotica Moran (Gammaproteobacteria: Enterobacteriaceae) and Regiella insecticola Moran (Enterobacteriales: Enterobacteriaceae) reached 100%. Notably, the infection rates of Spiroplasma and Rickettsia varied across host plants. Fitness assessment revealed that aphids performed better on their natal hosts, exhibiting shorter nymphal development times and higher fecundity. S. symbiotica had contrasting effects on aphids based on their origin. It prolonged the development duration and decreased the intrinsic rate of increase (r_m), net reproductive rate (R₀), and finite rate of increase (λ) in aphids collected from plant A. graveolens. However, for aphids collected from plant C. monnieri, it shortened the doubling time (DT) and improved r_m, R₀, and λ, while prolonging the mean generation time. Our studies are the first to investigate the infection status and role of facultative endosymbionts in aphid S. heraclei, extending the documented effects of plant diversity to fluctuations in the infection rate, with potentially far-reaching consequences for related endosymbionts’ ecosystem processes.