Cloning, Expression, and Odorant Binding Characteristics of the Chemosensory Protein 1 in Asecodes hispinarum, a Parasitoid of the Coconut Leaf Beetle.

Asecodes hispinarum (Hymenoptera: Eulophidae) is an endoparasitic wasp and efficient biological control agent of the coconut leaf beetle, Brontispa longissima, a significant pest of more than 20 palm species. Due to its effectiveness against B. longissima, A. hispinarum is extensively utilized in the pest management of palms such as coconut, betel nut, and oil palm. Olfaction plays a crucial role in insect behaviors such as finding food, selecting oviposition sites, and locating mates. Despite the critical role of olfaction in host-seeking behavior, the molecular basis of chemoreception in A. hispinarum remains unexplored. In a previous study, we identified several olfaction-related genes in A. hispinarum through transcriptome sequencing and bioinformatics analysis. In the current study, the chemosensory protein gene 1 (AhisCSP1) of A. hispinarum was cloned, and real-time PCR was employed to assess the expression levels of AhisCSP1 across different developmental stages and adult tissues in A. hispinarum. Additionally, the odorant binding characteristics of AhisCSP1 were examined using in vitro protein expression technology and fluorescence competitive binding assays. The real-time PCR results indicated that AhisCSP1 was expressed at all developmental stages, with higher expression levels in the adult stage compared to other stages. Furthermore, AhisCSP1 expression was specific to (A) hispinarum antennae, with no expression detected in the head, thorax, abdomen, legs, or wings. A fluorescence competitive binding assay revealed that AhisCSP1 can effectively bound to the coconut volatiles L-α-terpineol, benzyl alcohol, 3-phenylpropionic acid pentyl ester and 2-ethyl-1-hexanol, with binding constants of 21.26, 25.42, 27.96, and 39.72 µmol/L, respectively. Among the four volatiles of (B) longissima larvae, AhisCSP1 demonstrated a strong binding capacity with isohexadecane, with a binding constant of 19.76 µmol/L, a medium binding capacity with pentadecane, with binding constant of 34.28 µmol/L, and a weak binding capacity with butyl benzoate and methyl eugenol, with binding constants of 53.45µmol/L and 58.27µmol/L, respectively. These findings suggest that AhisCSP1 may play a dual role in (A) hispinarum's host location by sensing the volatiles from both its host, (B) longissimi and the host habitat, i.e. palm species. Furthermore, these results suggest that AhisCSP1 could be a potential target for enhancing biological control strategies against B. longissima.