Circadian pattern in attendance of aphid colonies by ants

Ant-attendance of aphids is one of the subjects of interest in ecological studies as a reciprocal service providing benefits to both groups involved. The behavioural patterns in this relation depend on many factors, e.g. biology of the species involved, aphid host plants, activity of natural enemies and abiotic factors. In this respect, the circadian pattern of ant-attendance was almost unknown. The paper presents the results of the pattern of such circadian activity of ants Lasius niger and L. emarginatus attending six aphid species (Panaphis juglandis, Aphis grossulariae, A. urticata, A. umbrella, Myzus persicae and Aphis fabae) feeding on various types of plants and having various dependence of trophobiosis. The highest number of ant workers in aphid colonies was observed at night and dawn, while the lowest was just after solar noon. The circadian pattern of ant activity strongly depends on the weather, especially temperature and relative humidity, with the highest abundance of ants during humid and cool weather. The possible interconnection between the temperature-dependent activity of ants and the water-dependent physiological condition of certain plants is discussed and indicated as an explanation. The issue of possible work division among ant workers attending aphids as an explanation of the observed pattern of activity remains open.