Beetles prefer steeply angled crevices: effects of wood surface structure on the initiation of hole boring by Platypus quercivorus

ABSTRACT

Japanese oak wilt is caused by the pathogen, which is introduced into oaks by the ambrosia beetle Platypus quercivorus of which male initiates to bore. In the field, the entrance holes of beetles have been observed primarily in bark crevices. We hypothesized that male P. quercivorus initially distinguish the bark surface structure and then determine the hole boring site. To test this hypothesis, we observed the initiation of hole boring behavior by P. quercivorus under laboratory conditions. We prepared pieces of Quercus alba with 21 crevice patterns created by changing the opening angle and gap width. Each wood piece was placed in a plastic case and a male P. quercivorus was introduced into the case following flight in a flight mill. The male beetles were monitored for 30 min and the following three behaviors were recorded: whether the beetle recognized the crevice, whether the beetle stayed in the crevice for more than 30 s, and whether the beetle bored a hole in the crevice. Generalized linear models were constructed to clarify which factors (angle and width) influencing beetle behavior. Model analysis revealed that gap width affected only the staying behavior, whereas the opening angle affected all three behaviors. The probabilities of these behaviors occurring increased with a decrease in opening angle, though this trend was weak in hole boring behavior. Our results indicate that P. quercivorus detects a suitable surface structure and subsequently determines the best hole boring site based on structural characteristics, particularly the angle of the crevice opening.

KEYWORDS:

• Bark crevice
• entrance hole
• flight mill
• Japanese oak wilt
• platypodinae

Acknowledgments

We sincerely thank all members of the Laboratory of Forest Biology, Kyoto University, for advice and support during our experiments. We acknowledge the assistance of Drs. Y. Fujii and Y. Fujiwara, Kyoto University, for preparing the wood materials. We are also grateful to Mr. H. Ogata for assistance in obtaining the dead tree attacked by P. quercivorus. We also thank Dr. R. Okada, Kobe University, for assistance in preparing the flight mill apparatus.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was supported by JSPS KAKENHI (No. 18H02240)