Reduction in male progeny of Frankliniella occidentalis (Pergande) in the presence of competitor Frankliniella intonsa (Trybom): demonstration on potted bean plant

Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) and F. intonsa (Trybom) are sympatric flower-dwelling thrips infesting various agricultural crops in eastern Asia. In recent field observation, F. intonsa (native) was dominant regionally although F. occidentalis (invasive) has been generally considered as a major thrips species in Korea. To understand the asymmetrical occurrence pattern, we demonstrated the interspecific competition between the two sympatric species on cylinder caged potted bean plant. In both species, number of female progeny was significantly reduced in competition condition. But, male progeny of F. occidentalis decreased by 86% in competition condition, but such a reduction in male progeny was not found in F. intonsa. Therefore, male proportion of F. occidentalis decreased by 67% whereas that of F. intonsa was unaffected. Mean generation time of the two species was not different either competition or no-competition condition. These results indicate that, interference competition may exist between F. occidentalis and F. intonsa, and cause reduction male population of F. occidentalis.

Keywords: flower thrips · asymmetrical occurrence · invasive species · sex ratio · competition