Social interactions regulate resource utilization in a Tephritidae fruit fly Tamar Zur a , Esther Nemny-Lavy a , Nikos T. Papadopoulos b , David Nestel a, * a Department of Entomology, Institute of Plant Protection, Agricultural Research Organization, Israel b Laboratory of Entomology and Applied Zoology, Department of Agriculture, Crop Production and Rural Environment, University of Thessaly, Volos, Greece 1. Introduction An organism’s utilization of resources is modulated by both internal pre-established genetic mechanisms and environmental cues (Downer, 1981). Food-type and the pathways by which nutrients are metabolized are species-specific and genetically determined, while food-intake timing, selection of specific nutrients and activation or deactivation of biochemical pathways are regulated by the environmental conditions the organism encounters over its lifetime. Resource acquisition and its effects upon reproduction, devel- opment and longevity have been extensively studied in Tephri- tidae (‘‘true’’ fruit flies). Fruit flies’ selection and consumption of food have been shown to be affected by life-cycle stage and age (Webster et al., 1979; Galun et al., 1981; Nestel et al., 1985; Landolt and Davis-Hernandez, 1993), physiological and nutritional state (Galun et al., 1981, 1985; Nestel et al., 1986; Cohen and Voet, 2002) and food quality and availability (Zucoloto, 1987; Cangussu and Zucoloto, 1992; Canato and Zucoloto, 1993; Fernandes-da-Silva and Zucoloto, 1993). Patterns of food acquisition have also been suggested to be of central importance in metabolic regulation (Nestel et al., 1985, 1986, 2004a; Jacome et al., 1995; Warburg and Yuval, 1996; Butov et al., 2003; Romanyukha et al., 2004; Levy et al., 2005; Nestel et al., 2005; Nestel and Nemny-Lavy, 2008), modulation of life-history strategies (Carey et al., 1998a, 2005), reproduction, senescence and longevity of fruit flies (Webster and Stoffolano, 1978; Blay and Yuval, 1997; Kaspi and Yuval, 2000; Aluja et al., 2001; Carey et al., 2002; Prabhu et al., 2008). However, the metabolic courses of nutrients and energy metabolites, and the environmental and physiological regulation of resource partition- ing and allocation are poorly understood in this group of insects, and in other organisms as well. Enhanced understanding of these processes may shed light on fundamental processes of longevity, reproduction and senescence (Carey et al., 1998a; Novoseltev et al., 2004). Diet has been shown to affect egg-laying patterns and longevity in fruit flies (Carey et al., 2002; Nestel et al., 2005), and it has been postulated that diet may be a key factor in the physiological Journal of Insect Physiology 55 (2009) 890–897 ARTICLE INFO Article history: Received 25 March 2009 Received in revised form 25 May 2009 Accepted 26 May 2009 Keywords: Dacus ciliatus Food ingestion Lipids Protein Resource management ABSTRACT Previous studies have suggested that social interactions (e.g., the actions and reactions elicited by the interaction of co-specific individuals) induce individual fruit flies (Tephritidae) to ingest more food, especially protein-rich food. Changes in feeding behavior related to social interactions have been associated with reproduction (e.g., when different sexes are present), reproductive facilitation (e.g., when two females interact) and stress and aggression (e.g., flies of the same sex, or crowdedness). The present study investigated the effect of social interaction on the feeding, longevity and resource management of the Ethiopian fruit fly, Dacus ciliatus. Single flies and pairs of flies (of the same or different sexes) were confined to a small arena (the PUB system), in which we measured the amount of liquid food ingested daily by each fly. In addition, we sampled flies of different ages, extracted and quantified their lipid and protein contents, and related individual metabolic contents to the ingestion of a fructose and protein hydrolysate solution. Results showed that individual ingestion was significantly higher in flies maintained in pairs than in flies kept as solitary individuals. The highest intake rates were observed for the female–female pairs. In general, females ingested significantly greater volumes than males. Lipid contents tended to decrease progressively with age in flies kept as solitary individuals, especially in female flies, while lipid levels decreased and then increased in flies maintained in pairs. Protein trends were similar, although less pronounced than the patterns observed for the lipids. The flies kept as solitary individuals lived significantly longer than those kept in pairs. A resource-management analysis points to a decreased metabolic rate in flies kept as solitary individuals, as compared to paired flies. Results are discussed in view of theories of resource management and survival strategies. ß 2009 Elsevier Ltd. All rights reserved. * Corresponding author at: Institute of Plant Protection, Agricultural Research Organization, Volcani Center, P.O. Box 6, Beit-Dagan 50250, Israel. Tel.: +972 3 9683690; fax: +972 3 9604180. E-mail address: nestel@agri.gov.il (D. Nestel). Contents lists available at ScienceDirect Journal of Insect Physiology journal homepage: www.elsevier.com/locate/jinsphys 0022-1910/$ – see front matter ß 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jinsphys.2009.05.013