Every few years, you can hear the distinctive chirping of cicadas from sunrise to sunset. Among these, periodical cicadas of the genus Magicicada are known for making an appearance just once every 13 or 17 years.
While much is known about the biology, life cycle, and even mating behavior of periodical cicadas, a crucial question regarding their dietary habits has been the subject of a long debate. Once they are above ground, do these cicadas feed on anything?
The answer to this question is yes, according to a new study conducted by the Agricultural Research Service (USDA-ARS) at West Virginia’s Appalachian Fruit Research Station.
The significance of this discovery extends beyond mere curiosity. Periodical cicadas, especially Magicicada, are a concern for U.S. agriculture due to the potential damage they cause to orchard trees by laying their eggs on branches.
This process can prove lethal to young trees. As a result, many growers and nurseries strategically avoid planting new trees in the years corresponding with a Magicicada emergence.
The debate surrounding the feeding habits of adult cicadas stems from the elusive nature of their feeding signs. Unlike chewing insects, the needle-like mouthparts of cicadas leave almost no trace. Furthermore, their digestive systems are notoriously hard to study.
“The historical belief that adult cicadas in general do not feed on plants can likely be attributed to their lack of recognizable mandibular mouthparts and the inconspicuous nature of cicada feeding damage,” wrote the study authors.
“This Old World perception was apparently extended to Magicicada spp. upon the European colonization of North America, with the earliest literature repeating that adult cicadas do not feed at all, feed only on dew, or feed only rarely.”
“Further complicating the subject, one early work reported a distinction between the sexes in gut morphology and feeding habits, concluding that adult female Magicicada feed but males do not.”
To investigate, the USDA-ARS researchers examined adult male and female Magicicada from Brood X during their 2021 emergence across Maryland, Virginia, and West Virginia.
Their findings, published in the Journal of Insect Science, have uprooted the longstanding myth that adult cicadas do not feed.
In the guts of adult cicadas, the researchers found predominantly woody plant and apple tree DNA. Furthermore, 54 percent of the cicadas had DNA from more than one plant species.
To ensure that the plant DNA was not residual from the cicadas’ nymph stage, the team studied “teneral adults” – newly emerged cicadas that hadn’t fed yet.
“We tested teneral adults, or brand new adult Magicicada that had not had a chance to feed yet, to check for any leftover plant DNA,” said USDA-ARS research team leader Dr. James Hepler.
“We couldn’t find any plant DNA in the guts of teneral adults, so we can be reasonably sure that the DNA found in mature adult Magicicada was eaten during the adult stage, since no DNA carries over from the nymph stage.”
The cicada’s unique exoskeleton, which permits extensive water loss, coupled with the presence of amino acid-producing endosymbionts in adult Magicicada guts, indicates that they obtain nutrition as they feed on plant species.
With the mystery surrounding the cicada’s feeding habits resolved, USDA-ARS plans to delve deeper into the life cycle of Brood X and address other agricultural challenges related to their above-ground lifespan.
Additionally, future studies aim to explore the potential impacts of periodical cicadas on tree physiology.
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