Tuesday, May 30, 2017

Cicadas Emerge 4 Years Early

My guess was that the warmer temperatures is causing this directly. Their body processes will be running more cycles, which seems to me how they time their emergence. It would take a certain amount of metabolic activity to do whatever needs to be done to trigger their emergence. The scientists came to the same conclusion.

Scientists search for the mysterious cause, as millions of hatching bugs loudly buzz the night away
By Knvul Sheikh on May 26, 2017

Swarms of cicadas are unexpectedly crawling out from under trees from North Carolina to New Jersey. The red-eyed insects are almost impossible to miss; they fly around lazily, plunking into backyard barbeques and crashing into cars. They litter the ground with their crunchy husks as they molt. Most noticeably, they chirp en masse for their mates, producing a relentless, shrill buzz that is recognized as a song of summer. And within a month they are gone.

Different populations, or broods, of “periodical” cicadas emerge in distinct geographical regions during specific years, after spending a 13- or 17-year span growing underground. (Some “annual” species just emerge yearly.) Scientists were expecting to see Brood VI bugs in South Carolina and Georgia, which happened, but they got a surprise when Brood X cicadas also started appearing in North Carolina, Virginia, Maryland, the District of Columbia, Ohio and Indiana last week—four years earlier than anticipated.

Experts suspect a warming climate, with more warm weeks a year during which the underground nymphs can grow, could be triggering some cicadas to emerge ahead of their brood. “Temperature is everything,” says Marlene Zuk, an entomologist at the University of Minnesota. “When temperature changes, insects don’t just feel hot or cold. Their whole body doesn’t function normally.” And cicada nymphs may be growing to a threshold size so quickly that their internal biological clock is miscalculating when it is time to emerge, says Keith Clay, a biologist and cicada expert at Indiana University Bloomington. To calibrate these clocks, periodical cicadas likely rely on a variety of environmental cues such as changing seasons and ground temperature, he says. Nymphs feed on the xylem fluid (sap) from tree roots, and changes in the fluid composition as trees leaf out each spring may also help them gauge the passage of time. Entomologists reached this conclusion back in 2000 when they artificially sped up the blooming cycle of peach trees supporting cicada nymphs that were in their 15th year and tricked the insects into emerging a year early.


Nymph growth is key. “They have to be a certain size to come out as adults,” says Chris Simon, a cicada biologist at the University of Connecticut. Nymphs go through five stages of development, called instars, which last an average of four years each, except for the first one. The nymph’s internal clock may synchronize to these four-year instars, she says, which may explain why this year’s premature arrivals are ahead of schedule by four years. Even if they grow at different rates, most cicada nymphs wait for the rest of their group to catch up before squirming out of the dirt, she adds. When the soil reaches 64 degrees Fahrenheit in a given year, they all emerge together. Experts think evolution has favored this strategy as a way of overwhelming predators like birds and squirrels so cicadas can mate frantically and lay eggs before they die in a few weeks. But thousands of Brood X sightings implies the bugs are not waiting for their fellows. They are risking being eaten before they can reproduce, Simon notes.


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