Available online at www.sciencedirect.com Near-infrared spectroscopy as a tool in behavioural ecology: a case study of the weaver ant, Oecophylla smaragdina PHILIP S. NEWEY * , SIMON K. A. ROBSON† & ROSS H. CROZIER † *School of Marine and Tropical Biology, James Cook University, Cairns ySchool of Marine and Tropical Biology, James Cook University, Townsville (Received 28 January 2008; initial acceptance 11 April 2008; final acceptance 30 July 2008; published online 18 September 2008; MS. number: 08-00060R) 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, inves- tigating the behavioural response of insects to cuticular compounds usually involves the extraction and analysis of CHCs using gas chromatographyemass spectroscopy, which is a time-consuming and expen- sive 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 de- tected 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. Ó 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. Keywords: aggression; cuticular hydrocarbon; near-infrared spectroscopy; nestmate recognition; Oecophylla smaragdina; weaver ant Although the primary function of insect cuticular hydro- carbons (CHCs) is to prevent desiccation (Neville 1975), they also play a key role in insect recognition systems (re- viewed in Singer 1998; Howard & Blomquist 2005). CHCs may vary between closely related species (Mullen et al. 2008) and between sexes within species (Dapporto 2007; Liimatainen & Jallon 2007); they may signal changes in reproductive status (Cuvillier-Hot et al. 2004; Steiger et al. 2007) and frequently vary between colonies of social insects (Heinze et al. 2002; Denis et al. 2006). They can also be affected by diet (Liang & Silverman 2000; Richard et al. 2004; Buczkowski et al. 2005), and can vary within a species depending on geographical location (Jallon & David 1987; Fernandez et al. 2005; Buczkowski & Silverman 2006). A growing body of evidence indicates that many insects are able to act upon the information contained in CHCs. For example, in hybridizing zones of Chrysochus spp. (Co- loeoptera: Chrysomelidae) a male’s choice of female is governed by recognition of CHCs (Peterson et al. 2007). Males of the fruit fly Drosophila melanogaster use CHCs on the female’s cuticle to assess how many times she has previously mated (Friberg 2006). Male ball-roller scarabs, Canthon cyanellus cyanellus, recognize females by their cu- ticular compounds (Ortiz-Dominguez et al. 2006b). Among social insects, the detection and use of CHCs as signals of fertility is well established (reviewed in Monnin 2006), as is their use in differentiating between nestmates and other conspecifics (reviewed in Dani 2006). Investigating the behavioural response of insects to cuticular compounds usually involves the extraction and Correspondence: P. S. Newey, School of Marine and Tropical Biology, James Cook University, P.O. Box 6811, Cairns QLD 4870, Australia (email: philip.newey@jcu.edu.au). S. K. A. Robson and R. H. Crozier are at the School of Marine and Tropical Biology, James Cook Univer- sity, Townsville QLD 4811, Australia. 1727 0003e 3472/08/$34.00/0 Ó 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. ANIMAL BEHAVIOUR, 2008, 76, 1727e1733 doi:10.1016/j.anbehav.2008.07.025