The apple buprestid beetle, Agrilus mali Matsumura (Coleoptera: Buprestidae), can respond to various volatiles, but the underlying mechanism of odorant perception for this insect is poorly understood. Here, we cloned A. mali’s odorant-binding proteins 3 (AmalOBP3) and 8 (AmalOBP8) and characterized their expression patterns and binding profiles. Sequence and phylogenetic analyses showed that AmalOBP3 and AmalOBP8 were distributed in the classic and minus-C OBP subfamily, respectively. AmalOBP3 was specifically and abundantly expressed in antennae of both sexes. AmalOBP8 displayed high transcript levels in antennae of both sexes, abdomens of males, and wings of both sexes. Both AmalOBPs exhibited much higher expression in male antennae than in female antennae, suggesting that they could be important in perception of male-specific olfactory cues (e.g., some sex pheromones). Out of the 40 odorant ligands tested, AmalOBP3 and AmalOBP8 bound to 15 and 21 different odorants, respectively, indicating a distinct and selective binding profile for them. Both AmalOBPs seemed to have very strong binding affinity to aliphatic alcohols and aldehydes with 12 to 15 carbon atoms. Alcohols, esters, and terpenoids were more likely to be good ligands for both AmalOBPs than aldehydes and alkanes. Together with its broad expression in different tissues, strong binding with higher numbers of putative ligands for AmalOPB8 means that this protein can have more extensive functional roles in chemosensation of A. mali. Our results provide insights into the molecular basis of chemosensation in A. mali, as well as a basis for developing detection, monitoring, and management tools for this serious pest.

The apple buprestid beetle, Agrilus mali Matsumura, is an invasive pest causing significant damages to rare wild apple forests of Xinjiang. The morphology, abundance and distribution of antennal sensilla in both sexes of this pest were examined. We found that the antennae of A. mali females were longer than those of males. Five types of antennal sensilla were characterized, including trichodea (subtypes Tr.1, Tr.2, and Tr.3), chaetica (subtypes Sc.1, Sc.2, Sc.3, and Sc.4), basiconica (subtypes Ba. 1, Ba. 2, Ba. 3 and Ba.4), Böhm bristles (subtypes BB. 1, and BB. 2), and multiporous grooved sensilla. The most abundant sensilla of Ba.2 tended to occur mainly on flagellomeres 5–8 in both sexes. The last three flagellomeres tended to have the most abundant Tr.1 in both sexes. Overall, the abundance and distribution of these sensilla appeared to be highly conserved in both sexes, and their olfactory organs seemed to cluster on flagellomeres 6–8. However, some sex dimorphisms were also observed. Tr.3 and BB.2 were found only in females. Sensilla of Sc.2 were found on the pedicel and first two flagellomeres only in males. When compared with males, females showed a higher number of Sc.3, but a lower number of Sc.4 on the pedicel. These results indicate that contact cues could be important in intersexual communication in A. mali. The functional roles of these sensilla and their implications in A. mali behaviors are discussed, and further studies of identified chemosensitive sensilla can provide a foundation for developing semiochemical-based management strategies.

Increasing temperature and CO₂ concentrations can alter tritrophic interactions in ecosystems, but the impact of increasingly severe drought on such interactions is not well understood. We examined the response of a wheat-aphid-parasitoid system to variation in water-deficit stress levels. Our results showed that arid area clones of the aphid, Sitobion avenae (Fabricius), tended to have longer developmental times compared to semiarid and moist area clones, and the development of S. avenae clones tended to be slower with increasing levels of water-deficit. Body sizes of S. avenae clones from all areas decreased with increasing water-deficit levels, indicating their declining adaptation potential under drought. Compared to arid area clones, moist area clones of S. avenae had a higher frequency of backing under severe water stress only, but a higher frequency of kicking under well-watered conditions only, suggesting a water-deficit level dependent pattern of resistance against the parasitoid, Aphidius gifuensis (Ashmead). The number of S. avenae individuals attacked by the parasitoid in 10 min showed a tendency to decrease with increasing water-deficit levels. Clones of S. avenae tended to have lower parasitism rates under treatments with higher water-deficit levels. The development of the parasitoid tended to be slower under higher levels of water-deficit stress. Thus, the bottom-up effects of water-deficit stressed plants were negative on S. avenae. However, the top-down effects via parasitoids were compromised by water-deficit, which could favor the growth of aphid populations. Overall, the first trophic level under water-deficit stress was shown to have an indirect and negative impact on the third trophic level parasitoid, suggesting that parasitoids could be increasingly vulnerable in future warming scenarios.