Microclimate temperatures impact nesting preference in Megachile rotundata

The temperature of the nest influences fitness in cavity-nesting bees. Females may choose 14 nest cavities that mitigate their offspring’s exposure to stressful temperatures. This study aims to 15 understand how cavity temperature impacts the nesting preference of the solitary bee Megachile 16 rotundata under field conditions. We designed and 3D printed nest boxes that measured the 17 temperatures of 432 cavities. Nest boxes were four-sided with cavity entrances facing northeast, 18 northwest, southeast, and southwest. Nest boxes were placed along an alfalfa field in Fargo, ND 19 and were observed daily for completed nests. Our study found that cavity temperature varied by 20 direction the cavity faced and by the position of the cavity within the nest box. The southwest 21 sides recorded the highest maximum temperatures while the northeast sides recorded the lowest 22 maximum temperatures. Nesting females filled cavities on the north-facing sides faster than 23 cavities on the south-facing sides. The bees preferred to nest in cavities with lower average 24 temperatures during foraging hours, and cavities that faced to the north. The direction the cavity 25 faced was associated with the number of offspring per nest. The southwest-facing cavities had 26 fewer offspring than nests on the northeast side. Our study indicates that the nesting box acts as a 27 microclimate, with temperature varying by position and direction of the cavity. Variation in 28 cavity temperature affected where females chose to nest, but not their reproductive investment.