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.