Effect of landscape complexity, nesting substrate, and nest orientation on cavity-nesting solitary bees in southern Punjab, Pakistan

Solitary bees are in constant decline due to climate change, pesticide toxicity, and habitat loss. Provision of nesting sites is an important conservation strategy. Various factors affect bee nesting, including parasitism, entrance orientation, nesting substrate type, and diameter. This study explored the impact of nesting substrate, cavity diameter, and entrance orientation on solitary bee nesting preferences. Additionally, it investigated the influence of landscape type and seasonality on bee nesting efficiency which is the ability of a bee to successfully establish nest. Trap nests were placed at eight locations, representing five landscapes (forest, desert, agriculture, peri-urban, and urban). These trap nests had five different nesting substrates (bamboo reeds, wooden blocks, wooden logs, mud blocks, and paper tubes). At each location, four traps were set in all directions. The results showed maximum cavity occupation in south-facing nests. Peri-urban landscapes were the most favored for nesting, followed by forests. Solitary bees primarily preferred bamboo reeds for nesting, with peak occupation from April to June. Bees favored cavities with 6- and 8-mm entrance diameters, while wasps occupied smaller diameters (< 5 mm). Overall, bee species occupied fewer nests compared to parasitic wasps. Future research should explore brood chamber numbers and species-specific nesting preferences for bees, along with the impact of cavity microclimate on bee growth.