Pesticides are linked to global insect declines, with impacts to biodiversity and essential ecosystem services. In addition to well-documented direct impacts of pesticides at the current stage or time, potential delayed “carryover” effects from past exposure at a different life stage may augment impacts to individuals and populations. We investigated the effects of current exposure and the carryover effects of past insecticide exposure on the individual vital rates and population growth of the solitary bee, Osmia lignaria. Bees in flight cages freely foraged on wildflowers, some treated with the common insecticide, imidacloprid, in a fully crossed-design over two years, with insecticide exposure or no exposure in each year. Insecticide exposure reduced reproduction, directly to foraging adults and via carryover effects from past exposure. Repeated exposure across two years additively impaired individual performance, leading to a nearly four-fold reduction in bee population growth. Exposure to even a single insecticide application can have persistent effects on vital rates and reduce population growth for multiple generations. Carryover effects had profound implications for population persistence and must be considered in risk assessment, conservation, and management decisions for pollinators to mitigate effects of insecticide exposure.