Disappearing mosquitoes leave clues about basic ecology

Palmyra Atoll is a tiny speck in the Pacific Ocean, roughly 1,000 miles south of Hawaii and less than 3 square miles in area. Its only human inhabitants are small groups of scientists who use the island as a natural laboratory. For a long time, they endured attacks from another of Palmyra Atoll’s residents -- mosquitoes.

“It was really hard to do field work there during the day without getting massacred by mosquitoes,” said National Science Foundation (NSF) program officer Daniel S. Gruner. While working toward his doctorate at the University of Hawai‘i, Mānoa, Gruner conducted fieldwork on the atoll in 2003, studying insects attacking native Pisonia grandis trees.

But when researchers returned years later, they realized something was missing.

“One of the first things our team noticed was that we weren’t getting eaten alive by mosquitoes,” said Hillary Young, a researcher at the University of California, Santa Barbara. “One of the things about being out there historically was that we were constantly having to slather on repellant. We didn’t have to anymore.”

Mosquitoes active at night were still there. But the daytime pest, the Asian tiger mosquito, Aedes albopictus, was gone.What changed? In 2011, the U.S. Fish and Wildlife Service, The Nature Conservancy and Island Conservation began a multi-year campaign to systematically eradicate all of Palmyra Atoll’s 40,000 rats, an invasive species and the island’s only year-round mammal inhabitants. But the mosquitoes, in theory, could have survived the disappearance of the rats. Asian tiger mosquitoes are aggressive, daytime biters that will feed on non-mammalian species, and thousands of birds -- typical Aedes prey -- still called Palmyra Atoll home.

“We were asking ‘Where did all the mosquitoes go?’” Young said. Young is the senior author on a new, NSF-supported paper published in Biology Letters from a research team that worked to answer that question. The research project provided training for a new generation of scientists and showed that sometimes, being in the right place at the right time can take science in unexpected directions.

“This was really serendipity,” said Gruner, who served as a co-author in his capacity as a researcher at the University of Maryland. “If you’re prepared for a surprise, you can take advantage.”