Pathogens of soybean aphid and other aphid species present on other crops in soybean production regions were surveyed in Michigan in 2005 and 2006. Soybean aphid occurred at moderate to high numbers in 2005 (150 to 1,000 aphids per plant) and was much less common in 2006 as of July. Aphid pathogens were sampled four times each year. Fungal infection of soybean aphid was detected in early August of 2005 during or soon after peak aphid populations. All cases of soybean aphid infection were caused by the fungal species Pandora neoaphidis. Higher proportions of alates (up to 90 %) were infected than apterae (up to 3 %). Pandora neoaphidis also infected pea aphid on alfalfa, and spotted alfalfa aphid was infected by Zoophthora sp. Three other species of aphids were found on corn and wheat, but they occurred at low numbers and no visual signs of infection were observed. These results indicate that fungal pathogens contribute to soybean aphid mortality, epizootics occur, and other infections occur on aphids in alfalfa found in the soybean production region of Michigan.