Influence of trap nest dimensions on reproductive biology and offspring body size in two centris bee species (hymenoptera: apidae)

In this study, we examined how trap nest dimensions influence the offspring of two crop-pollinating bees, Centris (Heterocentris) analis (Fabricius, 1804) and Centris (Hemisiella) tarsata Smith, 1874 in two irrigated acerola orchards in Brazil. Trap nests with two lengths (10 cm and 15 cm) and four internal diameters (0.6, 0.8, 1.0, and 1.2 cm) were installed in 32 perforated wooden blocks (1,024 cavities) mounted on four steel shelves. Bee body size was assessed using head width, head length, and intertegular span. A total of 341 individuals of C. analis and 113 of C. tarsata were recorded. C. analis predominantly nested in cavities of 0.6 cm diameter and 15 cm length, while C. tarsata favored 0.8 cm diameter cavities of the same length. Natural enemy incidence was low, with Mesocheira bicolor being the most common kleptoparasite. Mortality rates were highest in narrower cavities (0.6 cm). Our findings demonstrate that offspring body size is more strongly influenced by trap nest diameter than length, highlighting the importance of nest architecture in the management and conservation of solitary bees. Optimizing nest dimensions can improve reproductive outcomes and support pollinator conservation in agricultural landscapes.