Antimicrobial Driven Plant Selection and Nesting Ecology of Megachile sp. in a Tropical Arboretum of the Wallacea Bioregion

Abstract

Solitary leafcutter bees (Megachile spp., Hymenoptera: Megachilidae) are key pollinators in tropical ecosystems, yet their nesting ecology and plant selection remain poorly understood in Southeast Asian biodiversity hotspots. This study aims to investigate the nesting behaviour, nest architecture, and plant associations of Megachile sp. in the Kawanua Arboretum, North Sulawesi, Indonesia, within the Wallacea bioregion. A total of 15 active ground nests were analysed using purposive sampling, and associated plant species were identified. Nests were constructed in soil at depths of 8.47 ± 2.93 cm, with entrance diameters of 11.00 ± 0.85 mm and an average of 5.93 ± 0.80 brood cells per nest. Significant positive correlations were found between nest diameter and tunnel depth (r = 0.903, p < 0.0001), and between diameter and brood cell number (r = 0.952, p < 0.0001). Eighteen plant species from eleven families were identified as nesting and floral resources. Nest construction materials were predominantly derived from plant species with documented antimicrobial properties, including Diospyros spp., Syzygium spp., and Etlingera elatior. These findings provide the first ecological evidence from the Wallacea region suggesting that Megachile sp. may preferentially select antimicrobial-rich plant species for brood protection. This study highlights the ecological linkage between nesting behaviour, plant chemistry, and habitat structure, with implications for pollinator conservation in tropical landscapes.