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.