Explained | Delta plus variant, gain-of-function research, Nagaland bat viruses study, and periodical cicadas

Explained | Why do periodical cicadas stay underground, and when do they emerge?

The story so far: The latest phenomenon that has taken America by storm is the song of the cicadas. Billions of cicadas have emerged across eastern parts of the United States. Periodical cicadas, so called because of their 13- or 17-year life cycle, most of which is spent underground, emerge from their earthy digs to romance, reproduce and retire. This year is the year of the Brood X periodical cicadas. Here, X stands for the Roman numeral and refers to the sequence of emergence. Certain questions arise in the research on cicadas — how do they grow underground, what do they eat during their 13- or 17-year nymph stages spent burrowed in, or how do they know it is time to emerge?

When was this phenomenon first recorded?

Periodical cicadas of the genus Magicicadae have intrigued entomologists since they were noticed. Though Native Americans in the east of America knew about them earlier, the earliest recorded mention of these insects was in 1633 (there is some doubt whether this was in 1631 or 1634) by William Bradford, the governor of Plymouth Colony in America, according to Gene Kritsky’s article in American Entomologist in 2001. This area later developed into the town of Plymouth, Massachusetts. The next mention was in 1666 by an unsigned note published by Henry Oldenberg where he referred to “swarms” of “locusts”. However, these insects are neither locusts nor do they swarm.

How did the evolution of lineages take place?

As species, periodical cicadas are older than the forests that they inhabit, write John Cooley and Chris Simon in an article in The Conversation. Molecular analysis has shown that about 4 million years ago, the ancestor of the current Magicicada species split into two lineages. Some 1.5 million years later, one of those lineages split again. The resulting three lineages are the basis of the modern periodical cicada species groups, Decim, Cassini and Decula. Each of these three species has 13-year and 17-year broods.


Why is the present emergent population called Brood X?

The term ‘brood’ is used to refer to all periodical cicadas that emerge the same year and occupy a geographically contiguous area. Charles Marlatt assigned roman numerals to designate their year of emergence, and the sequence started arbitrarily in 1893. The brood with the 17-year cycle that emerged in 1893 was denoted Brood I and so on. So the 17-year broods were designated I to XVII, and the 13-year broods were designated XVIII to XXX.

Why are they called periodical cicadas?

These cicadas spend most of their lives underground. They grow burrowed in their earthy homes by feeding on root xylem for 13 or 17 years. During this time, they complete five developmental stages, known as “instars”, entirely underground. The fifth-instar nymphs emerge from the ground by making holes and then transform into adults, only to perish approximately four weeks later. As adults, they gather in so-called chorus groups, where the males sing to woo the females. After mating, the female lays eggs in thin twiggy branches of trees and then dies. The eggs hatch and the nymphs drop into the earth like rain, burrowing into it. About 95% of the nymphs die, and the ones that are left feed on root sap and remain underground, till it is time to emerge. This is described in an article by Kathy S. Williams and Chris Simon in Annual Review of Entomology (1995).

In which parts of the U.S. are they found?

They are found to the east of the Great Plains in the U.S. and north of Florida, says Chris Simon, Professor of Ecology and Evolutionary Biology at the University of Connecticut, in an email. “They emerge earlier in the warmer southern areas (late April-May) and later in the colder zones (late May-June),” she adds.

Watch | Billions of Brood X cicadas emerge in U.S. after 17 years underground

How does climate impact them?

“In any given place, they come out only once every 13 or 17 years. Occasionally, part of a population will come out four years early and part four years late. With climate warming, we are seeing more four-year early emergences in larger numbers,” says Prof. Simon. For instance, the Brood X periodical cicadas were documented in 2017 too, according to an article in the Washington Post.

Are there periodical cicadas in India?

There are three species of cicadas of the genus Chremistica found in the Indian subcontinent — Chremistica mixta (found in Sri Lanka), C. seminiger (found in the Nilgiri hills) and C. ribhoi (discovered in Ri-Bhoi district of Meghalaya).

Mass emergence has been noticed only in the case of Chremistica ribhoi. The emergence takes place after dusk and once in four years. The phenomenon is well known among the villagers, who refer to the insect in the local Khasi language as ‘niangtaser’ (niang stands for “insect” and taser is believed to be derived from the name of the village “Iewsier”, which refers to the area in which the phenomenon occurs, and the forest region around it). This periodical cicada is used as food and fish bait and has been observed in May 2006 and in May 2010, according to a 2013 article in Zootaxa by Sudhanya Ray Hajong and Salmah Yaakop.

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Printable version | Jul 25, 2021 11:53:20 AM | https://www.thehindu.com/sci-tech/science/explained-why-do-periodical-cicadas-stay-underground-and-when-do-they-emerge/article34861124.ece

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