Water loss, not overheating, limits the activity period of an endothermic Sonoran Desert bee

Desert animals must manage the physiological stresses of heat and desiccation; evaporative heat loss mitigates overheating but exacerbates water stress. Small endothermic flying insects may be particularly vulnerable to overheating and water stress as a result of high surface area to volume ratios, but we lack quantitative understanding of the relative magnitude of these abiotic stressors in flying desert invertebrates, despite their ecological importance.
During the hottest and driest weeks of the year, many thousands of males of the Sonoran Desert digger bee (Centris caesalpiniae) flew near-continuously at elevated thorax temperatures for hours at mating aggregation sites, while occasionally fighting other males and digging for females.
To determine whether incapacitating high temperatures or water loss limited the activity period of male C. caesalpiniae, we assessed wet and dry body mass and water content through the activity period, crop volume and sugar content, microclimate selec..., Animals
In June 2020, we studied a mating aggregation of C. caesalpiniae males in rural Scottsdale, Arizona (GPS coordinates: 33.727, -111.799), focusing on respirometric measurements (Johnson et al., 2022), critical maximum temperatures, and field body temperatures. In May 2021, C. caesalpiniae males and females emerged at the same site. We measured crop volumes and sugar content, water loss rate, microclimate selection, and field body temperatures. In 2022, we measured critical water contents for C. pallida males and females collected in the flood plains of the Tonto National Forest (GPS coordinates: 33.552, -111.566), and for C. caesalpiniae females collected in Cottonwood, Arizona (GPS coordinates: 34.726, -112.017). We took all mass measures using a Mettler Toledo XPE56 XPE micro-analytical balance (accurate to 0.000001 g) unless otherwise specified.
Crop volume and sugar content
We measured the crop volume and sugar content of C. caesalpiniae males flying across 24 to 45 °C air te..., , # Water loss, not overheating, limits the activity period of an endothermic Sonoran Desert bee

Crop volume and sugar content values are included in
2021\_C\_caesalpiniae\_male\_Crop\_content.

Mark-recapture observations are present in
2021\_C\_caesalpiniae\_male\_Mark\_recapture.

Microclimate selection observations are present in
2021\_C\_caesalpiniae\_male\_Microclimate\_selection.

Metabolic water production for flying *Centris* *caesalpiniae* males is calculated in 2020\_C\_caesalpiniae\_male\_Respirometry\_water\_content\_and\_metabolic\_water.
This Excel file also contains tagma wet masses, dry masses, and water content.

2021\_C\_caesalpiniae\_Field\_mass\_decline contains the wet masses, dry masses, and water contents of large morph males flying in sunny field conditions.

Critical water content (CWC) values are included in two files.
2022\_C\_caesalpiniae\_female\_critical\_water\_content contains CWC values calculated for *C. caesalpiniae* females caught in Cottonwood, AZ....