Dining in the daylight: Nocturnal rhinoceros beetles extend feeding periods on host trees with reduced sap exudation

Abstract

While the Japanese rhinoceros beetleTrypoxylus dichotomustypically feeds on the sap of the oakQuercus acutissimaand the crape myrtleLagerstroemia subcostataduring the night, it exhibits feeding activity both during the day and night when it utilizes the ash treeFraxinus griffithii. However, the mechanisms underlying the variations in temporal activity patterns remain unknown. We compared feeding rates (measured as body mass increments) and sap exudation rates amongF. griffithii, Q. acutissima, andL. subcostata. We found that beetles feeding onL. subcostataandQ. acutissimaexhibited significantly higher feeding rates than those feeding onF. griffithii. No significant differences in feeding rates were observed betweenL. subcostataandQ. acutissima. The sap exudation rate was significantly higher forQ. acutissimathan forF. griffithii. However, there were no significant differences in the sap exudation rates betweenF. griffithiiandL. subcostataor betweenQ. acutissimaandL. subcostata. These findings suggest that lower feeding rates onF. griffithiiprolong the feeding duration, resulting in daytime activity. While the low sap exudation inL. subcostataseems inconsistent with high feeding rates on this host, this apparent contradiction could be related to the extended duration of sap exudation.