Journal of Theoretical Biology 226 (2004) 45–51 Nest architecture, activity pattern, worker density and the dynamics of disease transmission in social insects Marcio R. Pie a, *, Rebeca B. Rosengaus b , James F.A. Traniello a a Department of Biology, Boston University, 5 Cummington Str., Boston, MA 02215, USA b Department of Biology, Northeastern University, Boston, MA, USA Received 22 May 2003; received in revised form 11 July 2003; accepted 4 August 2003 Abstract Theroleofdiseaseintheorganizationofinsectcolonieshasbecomeanimportantfocusofresearchinevolutionarypathobiology, in which the relationship of sociality and disease transmission can be comparatively and experimentally analysed. In this paper we use an individual-based model of disease transmission to assess how an epidemic is influenced by worker density and activity level, the probability of disease transmission, and the structural organization of the nest. First, we observed in our model a nonlinear interaction between worker density and the probability of disease transmission: high levels of both factors interact to enhance the likelihood of an epidemic. Additionally, when we incorporated in our model the empirical observation that only a fraction of the worker population in social insect colonies is active at any given point in time, results suggested that relatively low levels of worker movementcanhaveasignificantimpactonthespreadofdisease,slowingitstransmissionthroughthecolony.Finally,wefoundthat nests having even a simple spatial separation of chambers could delay the spread of infection and diminish the severity of an outbreak.Theeffectofneststructureindelayinginfectionspreadbecamemorepronouncedasnestarchitecturebecameincreasingly unidimensional, as in the case of simple gallery nests. Therefore, nest architecture and worker activity patterns might indeed exert considerable influence on the dynamics of epidemics in social insects and should be incorporated into models of disease transmission. r 2003 Published by Elsevier Ltd. Keywords: Agent-based modeling; Epizootic; Infection 1. Introduction Recently, the impact of disease on insect colonies has been the focus of increased interest in the fields of sociobiology and ecological immunology (Schmid-Hem- pel, 1998). Parasites and pathogens are now known to influence attributes of social organization ranging from foraging behavior and genetics to colony life history (Feener, 1988; Schmid-Hempel and Schmid-Hempel, 1991, 1993; Keller, 1995; Orr et al., 1997; Rosengaus et al., 1998, 2000; Rosengaus and Traniello, 2001; Schmid-Hempel and Stauffer, 1998; Morrison et al., 1999; Sammataro et al., 2000). Nevertheless, several fundamental questions concerning how disease may spread among the inhabitants of the often densely packed social insect colonies remained poorly under- stood. For instance, nest architecture, which is a key factor in the evolution of division of labor in ants and affects the efficiency of colony operations (H . olldobler and Wilson, 1990), could influence the dynamics between parasites and their social hosts if the structure of the nest compartmentalizes workers and brood. The spread of diseases that require contact for transmission can be affected by the way in which the nest is constructed, because nest walls can limit the pattern of movement of workers. This influence should vary considerably among different species given that nest architectures range from single cavities and simple galleries to intricate and complex constructions (e.g. Noirot, 1970; von Frisch, 1974; Jeanne, 1975; Wcislo et al., 1993; Kleineidam et al., 2001; Cassill et al., 2002). Variationinthelevelofactivityofworkerscouldalso accelerate or inhibit the spread of disease because the rateofworkermovementwithinthenestcanincreaseor ARTICLE IN PRESS *Corresponding author. Tel.: +1-617-353-6977; fax: +1-617-353- 6340. E-mail address: pie@bu.edu (M.R. Pie). 0022-5193/$-see front matter r 2003 Published by Elsevier Ltd. doi:10.1016/j.jtbi.2003.08.002