Diel Feeding Activity and Thermoregulation by Japanese Beetles (Coleoptera: Scarabaeidae) within Host Plant Canopies

Patterns of feeding by Japanese beetles, Popillia japonica Newman, were studied in relation to time of day or night and to ambient temperature (Ta). We also measured beetles’ thoracic temperatures (Tth) at rest, during preflight warm up, and during flight, and observed their within-plant distributions in relation to sunlight or shade to gain insight regarding whether their in-field behavior involves physiological and behavioral thermoregulation. Finally, we studied startle response as affected by Ta and time of morning. Japanese beetles fed most extensively within trees from midmorning until late afternoon, but also substantially in evening (1800–2200 hours) and sparingly throughout the night so long as Ta was >15°C. Beetles in the field were capable of endothermy, maintaining elevated Tth independent of basking. At low to moderate Ta (19–32°C), nonflying beetles in shade or direct sunlight had Tth as much as 3.75 or 5.5°C higher, respectively, than Ta. Thoracic temperature was elevated during fl...