The U.S. Fish and Wildlife Service developed national guidelines to track species recovery of the endangered rusty patched bumble bee [Bombus affinis Cresson (Hymenoptera: Apidae)] and to investigate changes in species occupancy across space and time. As with other native bee monitoring efforts, managers have specifically acknowledged the need to address species detection uncertainty and determine the sampling effort required to infer species absence within sites. We used single-season, single-species occupancy models fit to field data collected in four states to estimate imperfect detection of B. affinis and to determine the survey effort required to achieve high confidence of species detection. Our analysis revealed a precipitous, seasonal, decline in B. affinis detection probability throughout the July through September sampling window in 2021. We estimated that six, 30-min surveys conducted in early July are required to achieve a 95% cumulative detection probability, whereas >10 surveys would be required in early August to achieve the same level of confidence. Our analysis also showed B. affinis was less likely to be detected during hot and humid days and at patches of reduced habitat quality. Bombus affinis was frequently observed on Monarda fistulosa (Lamiales: Lamiaceae), followed by [Pycnanthemum virginianum Rob. and Fernald (Lamiales: Lamiaceae)], Eutrochium maculatum Lamont (Asterales: Asteraceae), and Veronicastrum virginicum Farw. (Lamiales: Plantaginaceae). Although our research is focused on B. affinis, it is relevant for monitoring other bumble bees of conservation concern, such as B. occidentalis Greene (Hymenoptera: Apidae) and B. terricola Kirby (Hymenoptera: Apidae) for which monitoring efforts have been recently initiated and occupancy is a variable of conservation interest.