Subterranean nymphal development in cicadas presents challenges to researchers in accurately estimating the number of their developmental stages, although such information is crucial to understanding and predicting their population dynamics. While most studies have relied on head width as an attribute for life-stage determination to date, such character in cicadas can be highly variable and thus differentiation solely based on such morphology is prone to subjectivity in practice. Here, we propose a reliable method for instar estimation that is applicable to Hyalessa fuscata nymphs. We first obtained morphometrics of nymphs in all stages. Second, we computed logarithm-transformation and principal component analysis to extract a transformed variable that captures most of the variance of morphological characteristics. Third, k-means were computed to divide the dataset into distinct clusters assuming four-, five- and six life-stage scenarios for the best interferences of life stages. Finally, simple linear regression analysis was conducted to compare and select the best fit model. Our result shows that five nymphal stages best fit for H. fuscata nymphs. This method is expected to provide an easy-to-handle ecological tool for the study of life history of cicadas as well as other insects that have long life cycles and multiple developmental stages.
Bibliographical noteFunding Information:
This research was funded by the Graduate University of Science and Technology [grant number: GUST.STS.ĐT2020-ST03]; and the National Research Foundation of Korea [grant number. 2015R1A4A1041997]. We thank S. Kim, S. Gwak, W. Lee, S. Yu, J. Eum from Earth Loving Explorers of Donga Science for their assistance and support in field studies. We thank Dr. Zehai Hou for his generous help in sharing the head width size of Meimuna mongolica. We also thank Dr. Chris Simon for helping us improving the manuscript.
- Hyalessa fuscata
- K-means clustering
- Life-stage delimitation
- Linear regression
- Principal component analysis