INTRODUCTION
Colony size is related to several aspects of life history strategies in social insects, such as colony efficiency, division of labor, social interactions, task partitioning and reproduction (Oster and Wilson 1978; Anderson & Ratnieks 1999; Bourke 1999; Strohm and Bordon-Hauser 2003; Dornhaus et al. 2006; Hou et al. 2010; Fewell & Harrison 2016). Eusocial hymenopterans (bees, ants, wasps) live in colonies of variable size that are considered as “superorganisms” (Holldobler and Wilson 2009), in which each individual (i.e., unit, “cell”) cooperates for the survival and reproductive success of the major unit (i.e., colony, the “organism”). Therefore, colony size is linked to their life history and influences several aspects of collective organization (Gillooly et al. 2010; Dornhaus et al. 2012).
Alongside with honeybees (Apini), stingless bees (Meliponini) are advanced eusocial bees, which live in perennial colonies and possess a great diversity of nesting habits and life-history traits (Roubik 2006; Grüter 2020). They have a pantropical distribution (Michener 2013), and their colonies are generally composed of a single queen, hundreds to thousands of workers, and dozens to hundreds of males (Roubik 2006), with populations ranging from a few hundred to over a hundred thousand individuals (Wille and Michener 1973; Wille 1983; Grüter 2020). However, for most stingless bee species (417 species in the Neotropical region and 244 in Brazil; Pedro 2014), empirical data on colony size is scarce or absent, with the notable exception of Trigona spinipes(Fabricius, 1793), for which a recent study (Valadares et al. 2021) provided robust measurements and estimates and for Melipona rufiventris and M. seminigra (Roubik & Peralta, 1983). Where authors have provided estimates, in most cases, there is often no mention about the methods used (Lindauer and Kerr 1960; Wille and Michener 1973; Michener 1974; Wille 1983; Kerr et al. 2001), and in the handful of studies that present formulae for estimating colony size, there is no attempt to validate estimates using empirical data (i.e. counting number of individuals in studied colonies) (Ihering 1930; Aidar 1996). Moreover, these formulae are often based on single species, leaving uncertainty over their applicability to other species.
Several biological parameters (e.g., the number of immature bees, external activity, life expectancy of individuals, egg laying rate, size of brood combs, colony weight) are related to the number of individuals present in a colony. Therefore, they can be used as proxies to estimate the size of the colonies (DeGrandi-Hoffman et al. 1989; Malham et al. 2013; Duarte et al. 2016; Roldão -Bordoni et al. 2018). However, some of these parameters involve highly invasive sampling methods, in some cases provoking the death of sampled colonies (Delaplane et al. 2013). For this reason, the main aim of this study was to understand how some of these parameters relate to colony size and their viability as proxy measures of colony size.
Stingless bees are essential pollinators of many crops (Giannini et al. 2020). Therefore, knowledge on colony size is important for their use in crop pollination and for better management practices in meliponiculture (Jaffé et al. 2015). Thus, the main objectives of this study were: (i) to measure the colony size (number of adult bees) of five Amazonian stingless bee species and (ii) to determine biological parameters of colonies (number of immature bees, egg laying rate, external activity, food stocks) that covary with colony size.