UHI rises when urban area becomes warmer than its surrounding and is considered as one of the main reasons for cicada abundance in urban areas. Two cicada species, Cryptotympana atrata and Hyalessa fuscata, are more abundant in urban areas with high urban heat island intensities (UHI) than in areas with low UHI. Thermal responses are a measure of cicada adaptation to thermal conditions in the habitat. Hence, we hypothesized that cicadas inhabiting high UHI areas exhibited elevated thermal responses compared to those occupying in low UHI areas. We measured minimum flight temperature (MFT), maximum voluntary temperature (MVT), and heat torpor temperature (HTT) of C. atrata and H. fuscata in metropolitan Seoul. For each species, there were three treatments: high UHI, low UHI, and suburb populations. We discovered that MFT and MVT were similar across all thermal treatments for each species. There was no difference in HTT across three treatments in C. atrata, meanwhile the HTT estimate was significantly higher in H. fuscata with high UHI than in those with low UHI. These results may suggest that H. fuscata in areas of high UHI may have developed thermal adaptation to high temperatures.

In Korea, Cryptotympana atrata and Hyalessa fuscata are the most abundant cicada species, and their population densities were 2.8-9.5 times higher in urban areas than in rural areas. It has been suggested that the urban heat island effect (UHI), which is higher temperatures in urban areas than in surrounding areas due to human activities, underlied the population density differences between urban and rural areas. To elucidate the relationship between UHI and cicada population density, we compared cicada population densities in three groups: areas of high and low UHI in metropolitan Seoul as well as areas in the vicinity of Seoul. C. atrata and H. fuscata constituted almost 30% and 70% of the exuviae, respectively, collected across all sampling localities. Moreover, no difference in species composition was observed among groups. The densities of C. atrata and H. fuscata were 14 and 41 times higher in high UHI areas than in low UHI areas. Furthermore, the degree of UHI was significantly correlated with densities of both C. atrata and H. fuscata. In summary, these results support that higher temperatures during the development may cause population increases of C. atrata and H. fuscata.

Advertisement songs play an important role on species recognition and mate choice in cicadas. Males generate complex species-specific calling songs to attract conspecific females. In central Korea, Cryptotympana atrata, Meimuna mongolica and Hyalessa fuscata are widely distributed, yet their songs have not been described. We analyzed acoustic characteristics of these cicadas’ advertisement songs in temporal and spectral domains. In sum, C. atrata’s songs followed the pulse-echeme pattern, in which each echeme consisted of groups of pulses with the peak frequency of 6423 ± 589 Hz. In M. mongolica, the calling song had the pulse-echeme-combined echeme-phrase structure. A group of three echemes formed one combined echeme, and one full phrase comprised hundreds of combined echemes. Lastly, the calling song of H. fuscata was constructed of the pulseecheme- phrase structure, in which one full phrase included a train of low and high-frequency echemes and the ending echeme at the end of the phrase. The carrier frequency of low frequency echeme was 4576 ± 151 Hz and that of high frequency one was 14089 ± 628 Hz.

Five species of the subfamily Cicadinae are typically found in urban areas of central Korea, including Cryptotympana atrata, Graptopsaltria nigrofuscata, Hyalessa fuscata, Meimuna mongolica, and Meimuna opalifera. These species form multi-species choruses. We hypothesized that there is a negative relationship between dominance of choruses among cicada species. We tested this hypothesis by conducting the 24-h recording experiments in four localities: Gawcheon, Jamsil, Ewha University, and Yangpyeong. Based on the enumeration surveys of exuviae, the results of 24-h recordings showed that choruses of C. atrata and H. fuscata were negatively correlated with other in Jamsil and Ewha University, but were positively correlated with other in Gawcheon and Yangpyeong. Thus, it seemed unclear cicada species competed with each other negatively over. Males of C. atrata produced calling songs usually during the day at temperatures typically higher than 28 C°. However, males of H. fuscata produced calling songs throughout the day at a wide range of temperatures. As a result, the chorus of C. atrata dominated during the day, but that of H. fuscata in urban areas where the densities of C. atrata were sufficiently high.