Near-infrared spectroscopy as a tool in behavioural ecology: a case study of the weaver ant, Oecophylla smaragdina

Cuticular hydrocarbons (CHCs) play an important role in insect recognition systems. A growing body of evidence indicates that insects are able to act upon the information contained in CHCs. However, investigating the behavioural response of insects to cuticular compounds usually involves the extraction and analysis of CHCs using gas chromatography–mass spectroscopy, which is a time-consuming and expensive process. Near-infrared spectroscopy (NIRS) may provide a much faster and less expensive technique for studying the behavioural response of insects to cuticular compounds. Here we present a case study of intercolonial aggression in the weaver ant, Oecophylla smaragdina. The differences between colonies detected by NIRS were reflected in the behaviour of colony members. The level of aggression expressed by colonies towards intruders increased as the spectral distance between colonies increased. The variability in the aggressive response also increased as the breadth of within-colony variation in spectra increased. This demonstrates that spectra generated using NIRS contain information to which weaver ants are able to respond. We discuss the implications of this for behavioural studies that have previously depended upon the extraction and analysis of CHCs.