How A Native Mosquito Benefits From An Invasive Interloper | St. Louis Public Radio

How A Native Mosquito Benefits From An Invasive Interloper

May 27, 2019

As you’re swatting at swarms of mosquitoes this spring, take comfort in this fact: Our bloodsucking foes have their own parasites.

The tiny waterborne parasites only infect mosquitoes — but not every species is susceptible.

The invasive Asian rock pool mosquito, first found in Missouri in 2005, appears to be virtually immune to a protozoan parasite in Missouri. Biologists at Tyson Research Center now say this invasive mosquito acts like a vacuum, sucking up parasites that attack a native mosquito species.

Like clams and sponges, mosquito larvae spend their days filtering food particles out of the water.

That puts them at risk of accidentally eating parasites, said postdoctoral researcher Katie Westby.

“If you’re a mosquito, no matter what species you are, you’re going to encounter these parasites, and you’re going to ingest them,” Westby said.

Those parasites, known as gregarines, don’t always kill the mosquito host, but they can stunt their growth and affect reproduction.

Westby strongly suspected that the invasive rock pool mosquito was a “dead-end host” immune to the parasite — and wondered whether that might affect other mosquito species.

So she decided to create her very own mosquito farm last summer, using 40-gallon contractor buckets.

To understand how the invasive mosquito affected parasitism of the native species, Westby and an army of undergraduates set up a mosquito farm in the forest at Tyson Research Reserve.
Credit Kim Medley

Half had only the native eastern treehole mosquito, while the rest had a mix of the native eastern treehole species and the invasive rock pool mosquito.

To her surprise, when the native mosquito shared its habitat with the invader, parasite infection dropped by up to 80 percent.

“When Katie showed me the preliminary results, my jaw dropped,” said Kim Medley, director at Tyson Research Center. “It was just such a striking reduction in parasitism.”

So how was the invasive mosquito species reducing parasitism in its native counterpart?

The invasive mosquito is an “indiscriminate filter-feeder,” said Westby, meaning it sucks up tiny parasites from the water before they infect the native mosquito.

Larvae of the native eastern treehole mosquito, as seen through a microscope. Mosquito larvae are filter-feeders, which puts them at risk of accidentally ingesting microscopic parasites.
Credit Leslie Sterling

Medley cautions that the results are simply a first step toward understanding the complicated ways invaders can affect parasitism in native species.

“We’re not saying that this is an excellent outcome for the status or the persistence of this native mosquito,” Medley said.

Larger populations of the native eastern treehole mosquito aren’t necessarily desirable, given that it can pass a number of viruses to humans, including La Crosse encephalitis.

The team is already working on their next major experiment to understand how climate change may affect these mosquitoes and their parasites.

“People have a really thin appreciation for mosquitoes,” Westby said. “You know: we don’t like them, they bite us. But they’re really interesting ecological creatures.”

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