Daily locomotor activity rhythms of Raphidioptera and Neuroptera: nocturnal or diurnal, and why?

The daily activity patterns of insects are usually based on field observations where they are trapped by the light at night or collected in flight during the daytime. In this study, an actograph was used for quantitative examinations of the daily activity patterns of Raphidioptera and Neuroptera. In the actograph, a fine infrared beam (1 mm in diameter) passes the central part of a hyaline vessel, and interruptions of the beam by an insect’s movement placed in the vessel are successively pen-recorded on a chart paper sent from the recorder for several days. The obtained actograms suggested that adults of the most species of Neuroptera are nocturnally active and rest in the daytime. However, adults of Raphidioptera and some species of Neuroptera are active in the daytime or at dusk and dawn. Their daily activity patterns are discussed from the perspective of the relationships between their color patterns, palatability, and mimicry. In larvae of Neuroptera, most species of Chrysopidae were diurnally active irrespective of their adult nocturnality. The physiological mechanisms by which individuals shift from diurnal to nocturnal rhythms during developmental stages are still unknown.