By Liam Tiernan
It’s no secret that sea lamprey are one of the most costly and destructive invaders in the Great Lakes region – vicious bloodsuckers that ruin lake trout and whitefish fisheries across every Great Lake, causing shutdowns in fisheries in the mid-20th century and continuing to demolish native species today.
But new understandings of the functions and behaviors of these animals has given researchers a new way to try to combat this invasion, including the first vertebrate biopesticide ever discovered.
The Environmental Protection Agency registered 3kPZs, a lamprey pheromone, as a biopesticide in December, according to the U.S. Geological Survey.
This is a lamprey’s love call.
“A pheromone is a chemical cue for communication,” said Michael Wagner of the Michigan State University Fisheries and Wildlife Department. “A pheromone is an odor that’s intentionally released for the purpose of communicating with another individual.”
It could take several more years of research to make sure the biopesticide does not have unintended consequences and is ready for use. But registration gives the compound the legal foundation needed for eventual mass production.
“This pheromone (3kPZs) is released by a mature male, and initially we found that it will lure mature females to the spot it was released,” said Weiming Li, an MSU professor whose lab conducted the experiments leading to the breakthrough. “But it was found that immature males smell the compound and think ‘Hey, there’s a mature male there. That means there’s good spawning ground there, and maybe some other females,’ so they will go too.”
That means good news for those who are fighting invasive species in the Great Lakes.
“U.S. EPA registration of the sea lamprey mating pheromone opens the door for use of the pheromone in the commission’s sea lamprey control program, which protects Great Lakes fisheries from destruction caused by invasive sea lampreys,” Robert Hecky, chair of the Great Lakes Fishery Commission, said in a news release from the Geological Survey.
Suzette Kimball, the director of the Geological Survey, said in the same release that the pheromone was “a milestone for control of invasive species and protection of natural biodiversity.”
Today, the most common way of attempting to control lamprey populations is with a chemical called 3-trifluoromethyl-4-nitrophenol, which kills larval lamprey in their spawning grounds. This chemical has been used since the fishery collapses of the mid-20th century and has shown good results. However, this pesticide is sometimes harmful to other fish and to the larvae of other, nonparasitic species. 3kPZs might fix that.
Li said, “We can, in theory, modify the behavior of the animal to our advantage, for example directing them to a site where a pesticide will be more effective and less detrimental to existing wildlife, or direct them to a place where the larvae cannot survive, and then you don’t have to do anything.”
Other researchers, including Wagner, say that there may be other compounds that have even greater effects on lamprey behavior. Wagner’s research lies in “the smell of death,” an odor given off by a lamprey that has been attacked by predators. This odor is not a pheromone, but rather something called an “alarm cue,” a public information signal that other lampreys detect and avoid. In this video, published by Michigan State University, a tank full of adult lamprey is induced to flee by a small amount of this odor.
“We believe this is a compound that is aggregated in the skin, and when the animal is attacked, the skin is ruptured, and the compound is released into the environment,” said Wagner. “The species has evolved to smell it to detect predation events.
“Imagine being dropped off on a college campus to go to a football game. You’ve never been to the campus before and you don’t have a map. To find the stadium, you listen for the sound of the crowd. That’s what the odor of lamprey larvae does for a lamprey attempting to spawn,” continued Wagner.
“Now you know where the stadium is, but you have no information of where your seat is. You look at your ticket to find out. That’s the mating pheromone (3kPZs). However, when you get to the stadium, there are three guys fighting by one of the doors. You’ll go around and try to find another way in. That’s the alarm cue.”
With this analogy Wagner says that using these chemical signals, humans can possibly modify the behavior of migrating lamprey, using the “alarm cue” compounds to deter lamprey from delicate ecosystems and into larger waterways where fewer larvae will survive and more pesticides can be applied. In addition, 3kPZs and other mating pheromones can be used to concentrate the spawning population to increase the effectiveness of the pesticides.
“The dream is to one day map out their decision making process as they travel from large lake to watershed, from watershed to smaller bodies of water and use that information to try to acclimate them to a smaller number of rivers than they currently inhabit in order to kill more larvae with fewer pesticides,” said Wagner.”