Exploring the factors influencing the first singing date of a cicada, Graptopsaltria nigrofuscata: How will it be affected by climate change?

Climate change affects various scales of biotic interaction through phenological shifts. The emergence phenology of cicadas is ecologically important because these insects have large effects on the ecosystem as herbivores, as food resources, and in nutrient flux from subterranean resources. However, little is known about the weather factors affecting their emergence patterns in the field because their nymphal stages grow underground for several years. Here, we used long-term observation data on the first singing date (i.e. the first emergence of male individuals) of Graptopsaltria nigrofuscata, recorded by the Japan Meteorological Agency and citizen scientists throughout Japan, to (1) explore the most influential weather factors across a variety of time spans on the first singing date of G. nigrofuscata and (2) determine whether the temporal trend of the first singing date could be explained by temporal weather trends caused by climate change by using a state space model. Our results indicated that higher temperatures from midsummer to early winter in the previous year are bringing the cicadas' emergence forward, and the annual increase in temperature is causing the advancement of emergence patterns. Other weather factors, such as precipitation and humidity, did not have a strong effect. Our findings suggest that increased growth rates at the nymphal stage due to warming in the previous year influence cicada emergence timing. To understand the mechanisms of how rising temperatures are advancing cicada emergence, we need an approach based on the physiology and ecology of their nymphs.