Guy L. Bush (1929–2023) was an evolutionary biologist, entomologist, and John Hannah Distinguished Professor at Michigan State University.[1] He was also the first director of MSU's Graduate Program in Ecology, Evolution, and Behavior.[1] Bush is best known for his research on the process of speciation,[2] especially for his evidence of sympatric speciation in the apple maggot fruit fly, Rhagoletis pomonella, which shifted from using its native host, hawthorn tree, to using the domesticated apple tree in the last 150-200 years.[3][4]