Technical Abstract: Under sexual conflict, males evolve traits to increase their mating and reproductive success that impose costs on females. Females evolve counter-adaptations to resist males and reduce those costs. Female resistance may instead serve as a mechanism for mate choice if the male-imposed costs are outweighed by indirect benefits of screening out low quality males and producing “sexy sons.” Sexual harassment is a form of sexual conflict in which males make repeated, costly attempts to mate. Costs to female foraging or predation risk have been measured in several species, but measurements of direct fitness costs are rare. In the alfalfa leafcutting bee (Megachile rotundata Fabricius; Hymenoptera: Megachilidae), males harass females, and females resist all mating attempts. We placed bees in large, outdoor cages with different male-biased sex ratios. Harassment rate, nest progression, offspring production, temperature and food availability were measured daily for seven days. More male-biased sex ratios resulted in higher harassment rates. Harassment reduced the number of foraging trips and increased the duration of foraging trips made by females. Females produced offspring at a slower rate when subjected to higher rates of harassment. This demonstrates a direct link from sex ratio to harassment to female fitness under natural conditions. Now that the costs of harassment are confirmed, the haplodiploid genetic system of this species provides a unique opportunity to measure indirect benefits when females cannot receive “sexy son” benefits, but could instead receive benefits through daughters or grandoffspring.