A test of the sequential cues hypothesis in Chrysobothris flatheaded borers (Coleoptera: Buprestidae)

Flatheaded borers (FB; Chrysobothris spp.) are a genus of woodboring beetles that are polyphagous, utilizing many species of deciduous trees. Previous studies have suggested multiple cues for host-selection including attraction to volatiles emitted by herbicide damaged and transplanted trees (olfactory cues) and traps with purple coloration (visual cues). The sequential cues hypothesis poses that generalist insect herbivores use cues sequentially to locate hosts. In this study we aimed to understand the rank of importance of visual vs. olfactory cues in host selection by FB. In a full factorial design, we applied 8 treatments to red maple trees (Acer ), a common host of Chrysobothris femorata (Olivier). The treatments were applied as follows: 1) potted plant (control), 2) transplanted (transplanted control), 3) control with purple trap on stem, 4) control with herbicide damage, 5) control with purple trap and herbicide damage, 6) transplanted with purple trap on stem, 7) transplanted with herbicide damage, and 8) transplanted with purple trap and herbicide damage. One week after application, visual cues were measured as the spectral emittance of trunks where females commonly oviposit. Additionally, pigmentation in leaves (chlorophyll and carotenoids) were compared across treatments. Olfactory cues were also compared across treatments by collecting volatile emissions from each treatment. Trees were evaluated for borer attacks and successful larvae at the end of the growing season. Contrary to the sequential cues hypothesis, we predict that FB use multiple cues in unison with one another for host-selection.