Field observations and morphological measurements
Observations were conducted three times per day (from 09:00 to 10:00, 12:00 to 13:00, and 15:00 to 16:00) between June 1st and June 13th, 2022, excluding June 6th due to rain. Consequently, the maximum count of daily observations for each individual was three or fewer. During the observation periods, as the observer walked through the habitat, whenever we found individuals, we captured them using a net, weighed them using a scale (Pocket Scale MH-100) to the nearest 0.01 g, and subsequently released them at their original location. Previously unmarked (newly found) individuals were individually marked with on their left wing with a paint marker (PC–3M, POSCA) to render them individually identifiable (Figure 2B).
When we found cicadas, we also recorded plant species on which the individuals were located. In the study area, cicadas were found on multiple herbaceous plants such as Convallaria majalis (Lily of the Valley), Polygonatum odoratum var. pluriflorum (Solomon’s seal), Miscanthus sinensis (Chinese silver grass),Erigeron annuus (Daisy fleabane), Cirsium japonicum (Japanese thistle), and Thalictrum aquilegiifolium var.sibiricum (Meadow rue) (Figure 3). Among the plants, onlyC. majalis and P. odoratum have large leaves, and we predicted that these two species can effectively function as a shelter for T. isshikii . Thus, in the analysis of individual plant use, we focused on whether the cicadas were found in large-leafed (C. majalis and P. odoratum ) or small- and narrow-leafed plants (other plant species).
During the observation, we also recorded whether males produced calls or not. Tettigetta isshikii males consistently produced calling regardless of the presence of a quietly walking observer (Jiman Heo, personal observation). Males were assigned a score of 1 when engaged in calling and a score of 0 when silent.
Although we marked 41 males and 23 females in the field, we failed to sample a sufficient number of female individuals and lacked sufficient observations to conduct variance partitioning analyses. Thus, in this study, we focused on the analyses of data collected from males. We collected 103 behavioural and morphological samples from males, and repeated measurements were taken 2.45 on average per individual.