Olfaction is of great significance for insect mate-seeking and host-locating behaviors. Insect odorant-binding proteins (OBPs), especially those antenna-enriched OBPs, are thought to discriminate, capture and transport odorant molecules to olfactory receptors, but this has not been fully clarified in Bactrocera minax (Enderlein), an economically important pest of citrus crops. Our previous studies showed that seven OBP genes (BminOBP1-7) were identified from B. minax adults via a head transcriptome analysis, of which only BminOBP3 and 6 were highly expressed in antennae, suggesting an olfactory role. To confirm their functions, here, BminOBP3 and 6 were cloned, expressed in Escherichia coli cells. Binding properties of the recombinant BminOBPs with 13 volatiles, most of which can elicit a significant behavioral response from B. minax adults, were determined by fluorescent competitive binding assays. The results showed that Both BminOBP3 and 6 exhibited a remarkable selectivity towards the 13 ligands tested. BminOBP3 displayed strong binding affinity only with undecanol. BminOBP6 demonstrated strong binding affinity with undecanol and limonene among 13 ligands tested. Undecanol is believed to be main sex pheromone component of B. minax. Limonene is an important volatile compound enriched in citrus fruits. Taken together, we concluded that BminOBP3 and 6 may play a prominent role in the process of B. minax mate-seeking and host-locating behaviors through recognizing and transporting these volatiles. It is conceivable that this study will increase our molecular understanding of B. minax olfaction, facilitating the development of OBP-based behavioral interference that is potentially useful for the integrated management of B. minax.

Insect odorant-binding proteins (OBPs) are significant in binding and transporting odorants to specific receptors. Our previous study demonstrated that BminOBP3 exhibited a strong affinity with undecanol. However, the binding mechanism between them remains unknown. Here, using homology modeling and molecular docking, we found that the C-terminus (I116-P122), especially the hydrogenbonds formed by the last three amino acid residues (V120, F121, and P122) of the C-terminus, is essential for BminOBP3′s ligand binding. Mutant binding assays showed that the mutant T-OBP3 that lacks C-terminus (I116-P122) displayed a significant decrease in affinity to undecanol (K_i = 19.57 ± 0.45) compared with that of the wild-type protein BminOBP3 (K_i = 11.59 ± 0.51). In the mutant 3D2a that lacks F121 and P122 and the mutant V120A in which V120 was replaced by alanine, the bindings to undecanol were completely abolished. In conclusion, the C-terminus plays a crucial role in the binding interactions between BminOBP3 and undecanol. Based on the results, we discussed the ligand-binding process of BminOBP3.

To identify highly virulent Beauveria bassiana strains against Tuta absoluta and evaluate their biocontrol potential, four strains were phylogenetically characterized via ITS sequence analysis of rDNA and assessed for virulence against second-instar T. absoluta larvae. Foliar spray and root irrigation methods were used to establish B. bassiana endophytic colonization in tomato plants, with untreated plants serving as controls. A population life table was constructed to quantify the impact of colonized plants on larval development, fecundity, and key demographic parameters. Results showed variation in virulence among the four B. bassiana strains Bb1Bm, Bb2Bm, Bb1M, and BbC with Bb1Bm exhibiting the highest pathogenicity (85.00% corrected mortality at 1 × 10⁸ spores/mL). Maximum endophytic colonization in tomato leaves was observed 14 days post-inoculation with both foliar spray and root irrigation treatments. Life table analyses revealed that T. absoluta feeding on colonized plants exhibited significantly reduced survival rates, shorter adult lifespans, and lower female fecundity compared to controls. Key population parameters, including net reproductive rate (R₀), intrinsic rate of increase (r), and finite rate of increase (λ), were significantly reduced, while mean generation time (T) was significantly prolonged. These findings highlight the dual role of B. bassiana in T. absoluta management, demonstrating its potential as both a direct pathogen and an endophytic biocontrol agent capable of disrupting pest population dynamics.