Liriomyza sativaeBlanchard was the only agromyzid leafminer species reared from foliage of green onion,Allium cepaL. var.‘aggregatum’, collected at two commercial farms in the Waianae area of Oahu, HI. Mean weekly densities of live leafminers reached levels>13 larvae per leaf with mean seasonal densities of total mines as high as 20.6.In laboratory-conducted host plant-preference (choice and no-choice) tests, adult femaleL. sativaecolonized from the Waianae and Hawaii Kai areas of Oahu exhibited significantly greater host feeding and ovipositional preferences for foliage of ‘Henderson’ bush lima bean,Phaseoluslimensisvar.limenanusL. H. Bailey, compared to ‘multiplier’ onion. In no-choice tests, WaianaeL. sativaereared on onion and bush lima bean deposited significantly more eggs in onion compared with bean-reared Hawaii KaiL. sativae. However, when given a choice between onion and bean, preferences of bean-reared WaianaeL. sativaewere not significantly different from Hawaii KaiL. sativae. Onion-rearedL. sativaepreferred onion significantly more than bean-rearedL. sativaewhen provided a choice of the two host plants.Green onion has not been reported previously as a common host ofL. sativae. Based on differences in feeding and ovipositional preferences of WaianaeL. sativaecompared with Hawaii KaiL. sativae,it was concluded that Waianae populations ofL. sativaehad broadened their host range to include green onion. Factors conducive to host plant expansion ofL. sativaepopulations in the Waianae area of Oahu are discussed.