Like sick humans, sick crickets are usually lethargic, lose their appetite and show a decline in their sexual motivation. Shelley Adamo
It's a sexually transmitted disease worthy of a horror movie, one that renders its victims — crickets — infertile, but ramps up their desire to mate.
The virus IIV-6/CrIV devastated the cricket colony in a lab at Dalhousie University in Halifax. Biologist Shelley Adamo said by the time she noticed a problem, her entire colony had become infected.
The problem was that the crickets didn't show any of the usual signs of being sick. Like sick humans, sick crickets are usually lethargic, lose their appetite and show a decline in their sexual motivation.
"What really piqued my interest was that these infected crickets seemed perfectly normal," Adamo told CBC Radio's Quirks & Quarks in an interview that airs Saturday.
Well, almost normal. One normal behaviour they no longer engaged in was laying eggs.
Adamo opened up a female to figure out why.
Both males and females infertile
"That's when I noticed they were grossly abnormal," she recalled. "Their ovaries were shrivelled up and empty and they were filled with basically their fat tissue."
An analysis of the fat tissue showed it was "absolutely packed with viral particles."
The males didn't get away either. While their testes were intact, the sperm inside showed "little or no" ability to move.
Despite all that, the crickets showed no decline in their desire to mate.
"Not only did they have no decline, but the males in particular showed increased sexual motivation," Adamo recalled, noting that they started approaching and courting females far more quickly than healthy crickets.
"We're pretty confident these males are sterile, so the increase in sexual motivation can't really be benefiting them," Adamo said. "But … it can be helping the virus."
Experiments showed that the virus could be transmitted from cricket to cricket during mating or even during courtship rituals.
Adamo said the virus can ultimately kill its host. Interestingly, while it does infect young crickets, it doesn't normally kill them until they become sexually mature.
"They are living long enough to mate, which means they're living long enough to spread that virus."
All this leads to a sinister conclusion — that the virus may be altering the behaviour of its hosts in order to spread. That is something many parasites are known to do, but not in this particular way.
Like this virus, many parasites also make their hosts infertile so that energy normally used for reproduction of the host can be redirected to the reproduction of the parasite, Adamo noted in a Dalhousie University news release.
The virus IIV-6/CrIV only infects cold-blooded animals, so humans can't catch it. It has actually been known to infect crickets for about a decade, but this is the first time it has been documented to alter the behaviour of its hosts.
Adamo and her colleagues published their findings in the Journal of Experimental Biology.
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