1. Spatial variation in herbivory rates on a Neotropical ant-plant (Tococa guianensis) Tococa guianensis is a Neotropical ant-plant associated with ants of the genus Allomerus and Azteca, which are effective in defending their host-plants against insect herbivores. However, near to the limit of its southern distribution, isolated T. guianensis populations were found to persist despite the local absence of Allomerus and Azteca (obligate ants). Several hypotheses were proposed to explain the long-term persistence of these populations: (1) opportunistic ants fulfill – at least partially – the role played by obligate ants; (2) leaf trichomes (whose density is greater in plants without obligate ants) prevent herbivory; or (3) herbivore pressure might be lower where obligate ants do not occur. MATERIAL AND METHODS We performed a factorial experiment in three different sites: Aragarças and Cachoeira da Fumaça (sites with obligate ants), and Uberlândia (without obligate ants) (Figure 1A), by manipulating the presence of ants (with ants or ants removed) and the trichome density (intact or shaved leaves). Trichomes were removed with an electric shaver. Ants were killed with insecticide and the domatia isolated with cotton. Ant access was prevented applying Tanglefoot. Then, herbivory rates have been measured, during a 6 months-period, on leaves produced after the beginning of the experiment (Figures 1B-G). RESULTS CONCLUSIONS Figure 1. (A) Map of Brazil showing the location of the three study sites and the differents methods used in the treatments applied to plants : (B) shaving leaves, (C,D) insecticide application and domatia isolation, (F) Tanglefoot application, and (G) herbivory rates measuring. Figure 3. Effects of ants and trichomes on herbivory rates (leaf area damaged after 6 months). In Aragarças and Cachoeira da Fumaça Tococa is associated with obligate Allomerus ants whereas in Uberlândia it is associated with several opportunistic ant species. Figure 2. Temporal differences in herbivory damage on plants, at the three sampling sites. (A) (B) (C) (D) (E)(G) (F) Overall, our results indicate the existence of substantial variation in herbivore pressure among plant populations established in different locations. This may help to explain the existence of populations without mutualistic (obligate) ants. Our results also indicate that there is a strong spatial variability in the cost- benefit relationship between T. guianensis and its obligate ant associates. Alessandra Bartimachi Neves 1, Heraldo L.Vasconcelos 1 1 Laboratório de Ecologia de Insetos Sociais (LEIS), Instituto Universidade Federal de Uberlândia, Instituto de Biologia Rua Ceará s/nº Bairro Umuarama, 38400-902, Uberlândia – MG, Brasil  bartimarchi@yahoo.com.br Herbivory tended to be greater in leaves without trichomes, but the difference was not significant (Figure 3). Opportunistic ants did not affect herbivory rates in the site where obligate ants were not present (Figure 3A). Unexpectedly, however, obligate ants had a strong effect on herbivory rates in one site (F 1,34 = 35,288; p ≤ 0,001; Figure 3B) but not in the other (F 1,40 = 0,863; p = 0,359) (Figure 3C). In this latter site, herbivory rates were very low regardless obligate ants were removed or not. The average rate of herbivory varied among sites (F 2,64 = 20,445; p ≤ 0,001). Aragarças and Uberlândia had the highest rates (8,9 and 3,0 %, respectively), while Cachoeira da Fumaça had the lowest rate (0,8 %) (Figure 2). (A) (B) (C)