Recently, the native species Frankliniella intonsa (Trybom) (Thysanoptera: Thripidae) has been found to be regionally dominant over its invasive congener Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) in Korea. To understand the variation in patterns of occurrence in the field, the effect of competition on the biological attributes of the 2 thrips species was assessed in the laboratory. In a behavioral study, the effect of inter- and intraspecific competition in honey or pollen feeding was observed in a glass-slide arena, and we found both reproduction and longevity to be more reduced in F. occidentalis than in F. intonsa by competition. However, the extent of feeding marks on bean leaves made by both species (in competition) was not significantly different from that made by each species separately, except in the case of the F. intonsa larvae. In an experiment on potted bean plants, competition caused a greater reduction in numbers of F. occidentalis progeny than that of F. intonsa progeny. In behavioral observations, guarding and feeding times of adult F. intonsa were 8.5 and 1.5 times longer on honey, and 42.8 and 1.3 times longer on pollen than F. occidentalis, respectively. However, in intraspecific competition, none of the behavioral parameters in pollen feeding showed significant differences in either species, except for the “confronting” behavior. In conclusion, both interference and exploitation competition exist between the 2 thrips species, and in laboratory studies F. intonsa was more persistent, not only at feeding and guarding food sources, especially in the adult stage, but also in displaying higher reproduction and longevity. These may be the underlying mechanisms for the asymmetrical pattern of occurrence of the 2 thrips in the field.