Herbaceous strata with a dominant plant community 50 m in size were selected from 10 reservoir embankment areas in Shinan-gun, a southwestern island region of South Korea. Terrestrial insects were sampled 100 times with quantitative sweep sampling to investigate the insect fauna and their association with flora. The survey areas were mainly dominated either by Phragmites japonica or Miscanthus sinensis plant species. A total of 1,948 individual insects representing 173 species from 64 families within 9 orders were collected. The number of species was the highest at Jaeundo while the Shannon-Wiener diversity index was the highest at Saokdo. Similarity analysis showed that the insect species composition tended to be similar among survey sites with plant communities comprising the same dominant plant species. Species diversity was the highest in April while the number of individual insects was the highest in September. Petaphora maritima and Ochetellus glaber were the dominant and subdominant insect species, with a high frequency of occurrence at these sites. The results of this study could be applied towards biodiversity conservation and monitoring of reservoir embankment areas in the future.