Abstract: To clarify the thrips species, population dynamics, and diurnal activities of dominant species Frankliniella occidentalis and natural enemy Orius similis on Capsicum annuum in different planting environments, fivepoint sampling and clapping method were used to investigate the thrips and O. similis on three varieties of C. annuum in greenhouse (Luosi chili) and open field (Luosi chili, Taikong chili, and Zhoupi chili) conditions. The differences in thrips species and the population dynamics were analyzed under both planting environments. The diurnal activities of F. occidentalis were monitored by blue sticky traps. The results showed that 10 thrips species were recorded in the open field and six thrips species were recorded in the greenhouse onC. annuum. F. occidentalis was the dominant thrips species on C. annuumunder both planting environments. The peak period of F. occidentalis population occurred from late June to mid-July. Population size reached  33.4 and 18.0 individuals per plant in the greenhouse and in the open field in 2019, and  32.2 and 17.9 individuals per plant in 2020, respectively. Population size of O. similis peaked in midJuly, being 10-20 d later than that of F. occidentalis. The abundance of F. occidentalis in main activity period was significantly higher than that in early and late periods (P<0.05) in both planting environments. However,O. similis had the highest population in main and late activity periods (P>0.05). F. occidentalis had the highest abundance in the greenhouse (P<0.05). O. similis had the highest abundance in the open field (P<0.05) in the main activity period of both insect species. F. occidentalis was not active in night, but showed more frequent activity in daytime. The main activity time period in daytime was mainly from 12:00 to 16:00 in the open field and from 10:00 to 18:00 in the greenhouse. The species composition of thrips and the population dynamics of F. occidentalis and predator O. similis were significantly affected by the planting environment of C. annuum. Population growth of F. occidentalis was promoted while the population of O. similis was suppressed in the greenhouse condition. Our results suggested that the planting area of C. annuum in open field can be appropriately increased around the greenhouse to increase the natural population of O. similis, in order to enhance the natural control ability of F. occidentalis.

Key words: thrips species, dominant species, Orius similis, population dynamics, diurnal activity pattern.