Shillong, May 21: A new scientific study has revealed how rainfall and temperature patterns influence the seasonal behavior and diversity of cicadas in Meghalaya’s Ri Bhoi District. Conducted over three years by researchers from North Eastern Hill University (NEHU) and St. Edmund’s College, Shillong, the study is among the first to explore how these iconic forest songsters respond to changing ecological conditions in Northeast India.

The study conducted by PhD Scholar, Graham Bakynson Ranee under the supervision of Prof. S.R. Hajong at the Department of Zoology, North Eastern Hill University (NEHU), Shillong, has revealed how climate influences cicada activity in Meghalaya’s Ri Bhoi District. Over three monsoon seasons (2021–2023), Graham and his team including Dr. P.W.Shangpliang from the Department of Zoology, St. Edmund’s College, Shillong, documented the diversity, behavior, and habitat preferences of five cicada species in the region.

It focused on five cicada species recorded in and around the Botanical Survey of India’s experimental garden in Umiam between 2021 and 2023.

The five species—Pomponia linearis, Pomponia ramifera, Cryptotympana corvus, Eopycna repanda, and Scieroptera splendidula—were found to exhibit distinct patterns of emergence, behavior, and habitat preference based on climatic conditions. The most abundant, Pomponia linearis, was observed across forest edges and tall trees in human-influenced areas, contributing significantly to local biodiversity.

The researchers noted that July was consistently the peak month for cicada diversity, with three species active each year. This period coincided with higher rainfall (up to 567 mm in 2023) and warmer temperatures ranging from 28.8°C to 29.5°C. However, excessive rainfall beyond 150 mm sometimes led to reduced species diversity, suggesting that while cicadas depend on monsoon conditions, extreme precipitation may suppress their emergence or calling activity.

“These insects are deeply sensitive to the timing and intensity of monsoon rains,” said lead author Graham Ranee. “Their behavior reflects a delicate balance with temperature and rainfall, which likely evolved to optimize survival and reproduction.”

Cicadas were found to favor the stems and axes of tall trees over shrubs, likely due to the presence of a well-developed xylem system. These insects feed on tree sap and require sturdy vascular structures for sustenance. Trees like Pterospermum, Dysoxylum, and Tectona were preferred, while shrubby vegetation saw lower cicada presence.

Behaviorally, cicadas displayed varied daily rhythms. While Pomponia linearis was most active at twilight, Pomponia ramifera and others called in the morning or during the day. The study also observed group chorusing—males calling in synchrony—to amplify sound and attract distant females, especially in dense forest habitats where sound may otherwise dissipate.

Using standard biodiversity indices, the team found that the more abundant species like P. linearis and C. corvus had a positive impact on community diversity and ecosystem stability. Rarer species like S. splendidula played more specialized roles, possibly as indicators of microhabitat conditions.

The researchers conclude that cicadas, often overlooked in biodiversity surveys, are vital indicators of forest health and climate patterns. Their findings highlight the need for long-term monitoring and habitat conservation efforts in the Eastern Himalayas, especially as climate variability increases.

“This study gives voice to one of nature’s most rhythmic and responsive insect groups,” said Graham. “By listening to the cicadas, we are also learning how our ecosystems are changing.”

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