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We examined the movement of aphelinid parasitoids from overwintering refuges into adjacent crops of cantaloupe and cotton. Eretmocerus eremicus and Encarsia spp. are important parasitoids attacking Bemisia tabaci Biotype B in the desert agricultural region of southeastern California. Movement was studied by marking naturally occurring field populations of parasitoids with rubidium chloride (RbCl). Two experimental study sites, each composed of natural enemy refuge strips and adjacent crops of cantaloupe and cotton, were grown for 2 years. Marking studies using RbCl demonstrated that the refuge strips supported early-season parasitoids which later migrated into adjacent crops. Between 15 - 63% of Eretmocerus eremicus caught in adjacent cotton and cantaloupe originated from the natural enemy refuges. Between 40 - 75% of aphelinids attacking B. tabaci in natural enemy refuges were Encarsia spp. while 98% of the marked, captured parasitoids in adjacent cotton and cantaloupe were Eretmocerus spp. Refuges produced higher numbers of whiteflies, relative to parasitoids, during spring months, showing the importance of refuge plants selective for natural enemies. This is the first known study using the marker RbCl that shows movement of naturally occurring Eretmocerus between an overwintering location and an adjacent crop. [ABSTRACT FROM AUTHOR]