Why some butterflies sound like ants

October 29, 2014

Washington D.C, October 29, 2014 -- Ant nests can offer a lot to organisms other than just ants. They are well-protected, environmentally-stable and resource-rich spaces -- in many ways everything a tiny creature could ask for in a home. So long as you can live with an army of ants of course.

For the thousands of species of insects that squat inside ant nests, survival means finding ways to live with the ants -- by foiling the chemical cues ants use to distinguish friend from foe, for instance. Now a team of scientists from the University of Turin in Italy have been looking at how the would-be nest crashers also use sound as a protective countermeasure -- warping ant "words" to suit their own twisted tastes.

At the 168th Meeting of the Acoustical Society of America (ASA), to be held October 27-31, 2014 at the Indianapolis Marriott Downtown Hotel, the researchers will describe the latest research on one such ant-parasite pair -- Maculinea butterflies, which infiltrate the nests of Myrmica ants and spend most of their lives there as unwanted guests by mimicking the sounds produced by the ants themselves.

"Acoustic signals convey quite complex information, not only between worker ants while outside the colony, for example during foraging, but also within the nest and between castes," said Francesca Barbero, the lead researcher from the University of Turin, Italy. "We aimed at understanding whether some ant social parasites, such as butterfly larvae, could interfere with their host ant communication system."

Over the years, Barbero's team has recorded and analyzed the sound signals emitted by larvae and pupae of Maculinea parasites and by queens and workers of the Myrmica host ants. Observing similarities in the patterns between butterfly parasites and ant host's acoustic signals, they have investigated the role of those signals in the ant societies and host-parasite relationships by playing back recorded sounds to ant nests.

In an initial study published in the journal Science in 2009, Barbero's team collaborated with scientists from the Center for Ecology and Hydrology and the University of Oxford to show that the sounds queen ants make are distinctive sounds from worker ants inside ant colonies. The new work shows that the parasitic butterflies exploit that difference.

Maculinea species are so-called "obligated parasites," Barbero said, with lives that depend on two other species. Deposited as eggs onto the leaves or buds of one specific plant, they gorge themselves for 10-15 days then drop to the ground and wait to be found and ferried into a nest by a Myrmica worker ant.

Earlier research in the field showed that the butterfly caterpillars can "beg" like baby ants by secreting chemicals similar to those an ant larva would, fooling the workers into feeding the caterpillars as their own. But some of these imposing guests were actually given the royal treatment -- fed first and fed most, even in times of scarcity as the real ant larvae went hungry. This type of privilege is normally reserved for the queens of the nest, something that mimicking the begging brood could not account for.

To solve the mystery, Barbero and colleagues used a specially-manufactured microphone to record the noises of the ants and the caterpillars and played back the caterpillars' sounds within ant nests. By comparing the acoustic signals and analysing the responses of the ants, they found that the caterpillars indeed mimic the sound of their host queen ants and trick the worker ants into cleaning and feeding them in preference to their own offspring.

They also compared two populations of parasitic butterflies -- a predatory species that feeds on ant broods, and a cuckoo species that is fed directly by the worker ants. They found that while both species made queen sounds, the voices of the ones that depended on workers to feed them elicited a stronger response in the worker ants.

"This is consistent," Barbero said. "Once inside the host nest, the main difference between the two life strategies is that cuckoos need to be considered as colony members, predatory species need not to be discovered by ants."

The next step, she said, is to extend their research to assess the role of acoustical emissions in other butterfly-ant interactions.

"We hope our findings will boost research on acoustic communication in social parasites of ants," Barbero said, "[and] bring about significant advances in our understanding of the complex mechanisms underlying the origin, evolution and stabilization of host-parasite relationships."

Presentation 3aAB1, "Breaking the acoustical code of ants: The social parasite's pathway," by Francesca Barbero, Luca P. Casacci, Emilio Balletto and Simona Bonelli will take place on Wednesday, October 29, 2014, at 8:30 AM in Lincoln. The abstract can be found by searching for the presentation number here: https://asa2014fall.abstractcentral.com/planner.jsp

There are sound files of queen ants, worker ants, butterfly larvae and pupa available with this story. Contact: jbardi@aip.org

The 168th Meeting of the Acoustical Society of America (ASA) will be held October 27-31, 2014, at the Indianapolis Marriott Downtown Hotel. It will feature more than 1,100 presentations on sound and its applications in physics, engineering, and medicine. Reporters are invited to cover the meeting remotely or attend in person for free.


We will grant free registration to credentialed journalists and professional freelance journalists. If you are a reporter and would like to attend, contact Jason Bardi (jbardi@aip.org, 240-535-4954), who can also help with setting up interviews and obtaining images, sound clips, or background information.


Main meeting website: http://acousticalsociety.org/content/fall-2014-meeting

Program and Abstracts: https://asa2014fall.abstractcentral.com/planner.jsp

Live Webcast Oct. 29: http://www.aipwebcasting.com/webcast/registration/oct2014.php

ASA's World Wide Press Room https://acoustics.org/?page_id=165


ASA's World Wide Press Room is being updated with additional tips on dozens of newsworthy stories and with lay-language papers, which are 300-1,200 word summaries of presentations written by scientists for a general audience and accompanied by photos, audio, and video.


A press briefing featuring a selection of newsworthy research will be webcast live from the conference the afternoon of Wednesday, October 29. A separate announcement, which includes topics and times, will be sent later this week. Register at: http://www.aipwebcasting.com/webcast/registration/oct2014.php


The Acoustical Society of America (ASA) is the premier international scientific society in acoustics devoted to the science and technology of sound. Its 7,000 members worldwide represent a broad spectrum of the study of acoustics. ASA publications include The Journal of the Acoustical Society of America (the world's leading journal on acoustics), Acoustics Today magazine, books, and standards on acoustics. The society also holds two major scientific meetings each year. For more information about ASA, visit our website at http://www.acousticalsociety.org

Acoustical Society of America

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