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.

Consistent individual difference in a behavior is recognized as an important evolutionary force in niche variation and may be a personality trait, an inherent property of the individual. To understand whether aggressiveness is a personality trait, independent of resource holding potential (RHP) and resource value in animal aggression assumed by game theory models, I determined individual variation in aggressiveness by measuringboth positive phonotactic and acoustic responses to the broadcast stimulus repeatedly over the three-week period in males of Gryllus rubens. Factors tested included amplitude levels of the broadcast stimulus, body size, wing dimorphism, and age. The analyses of the generalized linear mixed models revealed that RHP factors such as age, wing dimorphism, and body size, were not significant for both positive phonotactic and acoustic responses. However, there seemed to be more aggressive responses to higher levels of amplitudes. The significant variance-covariance structures of the models indicated that some individuals consistently aggressive or nonagressive during the experimental periods. Because potential factors for resource values were controlled, and because potential RHP factors would not explain variation in aggressive responses, I concluded that aggressiveness is a personality trait that is not characterized by factors that I tested.