Populations of onion thrips, Thrips tabaci Lindemann (Thripidae: Thysanoptera), vary greatly in their ability to transmit Tomato Spotted Wilt Tospovirus (Tospovirus: Bunyaviridae) (TSWV). To gain an understanding of the basis for this variation, we compared the ability of five populations of T. tabaci from North Carolina and New York to transmit an isolate of TSWV obtained from an infected potato plant growing in a commercial potato field in Pasquotank Co., NC. The efficiency with which each population transmitted this isolate from infected to non-infected Emilia sonchifolia plants was measured. Based on the results, which indicated large and significant differences in transmission efficiency among populations, one population that transmitted TSWV efficiently and one that transmitted TSWV very inefficiently were chosen for further study. Reciprocal crosses were made between the efficient and inefficient transmitting populations. The resulting F1 progeny and progeny from the parental populations were tested for their ability to transmit TSWV. Our results indicate that the ability to transmit TSWV efficiently is inherited as a recessive trait.