In Shandong Province, China, the western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), was first detected in Qingdao in 2007. The pest is composed of 2 genetic strains or types based on analyses of the mitochondrial DNA gene, mtCOI. These are known as “the Greenhouse strain” and “the Lupin strain”, hereafter referred to as “WFTG” and “WFT-L”, respectively. To investigate the status and pathways of spread of this alien species in its new environment, we collected 78 samples of thrips from various plants in all of the 17 counties of Shandong Province during May–Jul, 2011. In total we made 16 collections of western flower thrips in 12 counties, and we analyzed the mtCOI gene of each of these samples. Most individuals (98.6%) in these 16 collections belonged to the WFT-G type and 3 (1.4%) belonged to WFT-L type. The results demonstrated that F. occidentalis has—without being noticed—become widespread in Shandong Province, and the main type is WFT-G. Field surveys coupled with genetic analyses proved to be helpful in revealing the invasion process including the invasion pathways or mechanisms, and such analyses may help in identifying approaches and options for prevention and management of the pest.