Study of the food-searching activity by smell in diving beetles of <i>Cybister</i> Curtis, 1827 and <i>Hydaticus</i> Leach, 1817 (Coleoptera: Dytiscidae) including the use of a microwave Doppler radar

To investigate how four species of Cybister Curtis, 1827 and one species of Hydaticus Leach, 1817 (Coleoptera: Dytiscidae) detect food, insects were provided with dried sardines using traps made by a three-dimensional printer. More than 83% of the beetles found the sardine hidden in the trap. When the two traps were set in an aquarium—one contained a dried sardine before extraction with boiled water, and another contained a dried sardine after extraction—more than 90% of beetles were caught in the trap with the sardine before extraction. In contrast, less than 3% of beetles entered the trap with the sardine after extraction. No feeding preference was found between the sardines before and after extraction. A microwave Doppler radar was used to quantitatively detect the behaviour using broth extracted from the sardines, and the broth enhanced the food-searching activity. These results suggest that these beetles use smell to find food, and their searching activities are induced by smell.