By Brigida SanchezJuly 23, 2019
"In 1897, alligator weed was first introduced into the continental United States, " says Chelsea Bohaty, a biologist with the U.S. Army Corps of Engineers. "It caused a lot of problems in the waterways because these invasive plants began blocking navigation channels and causing flood risk management problems."
Alligator weed outcompetes native plants throughout the state of Florida. As the plant grows into dense mats, the leaves that it sheds start to decay, robbing the waterbody of the oxygen it needs to support healthy aquatic wildlife.
"In the '60s the U.S. Army Corps of Engineers understood the impacts of the invasive species. Back then, the Corps focused a lot of our herbicide treatments towards the alligator weed, and we spent a great deal of money on treating the plant. The alligator weed flea beetle was a game-changer," explains Bohaty. The Corps no longer spends any money chemically treating alligator weed.
Invasive species cause economic losses of more than $138 billion in the U.S. annually. Before the use of the alligator weed flea beetle, the Corps would spend over one million dollars on managing the environmental impacts of the alligator weed in a given year.
Utilizing a strategy called Integrated Pest Management (IPM), scientists employ a combination of biological, mechanical, and chemical control measures to mitigate the impacts of invasive plants. Biocontrol agents such as the herbivorous alligator weed flea beetle, go through years of rigorous research. Biologists have to determine if the tiny agent will cause adverse impacts to plants and animals in the U.S.
"The alligator weed flea beetle is a classic success story for aquatic weed biocontrol, " says Nathan Harms, a research biologist at U.S. Army Engineering Research and Development Center. " There are a couple of things that make it such a good agent. First, both the adults and the larvae feed on the plant. The adults can live a long time, and the female can lay thousands of eggs. So a couple of fecund (productive) females with a short developmental time in all life stages consuming the plant are effective."
This little beetle measures 5 to 7 mm in length as an adult, and its name is an attribution to its flea like jumping capabilities. Under the right environmental conditions, the alligator weed flea beetle can make a significant impact. According to the University of Florida's Entomology and Nematology Department, the alligator weed flea beetle, once fully established, can decimate an acre mat of the alligator weed.
"The beetle has already established itself in Florida. They are doing their job out there right now," says Bohaty, who coordinates and participates in the collection of the beetles.
Chelsea is the lead biologist for the Corps' Alligator Weed Flea Beetle Program. On this particular morning, the collection takes place on Lake Woodruff with five airboats flying swiftly through the water to each mat of alligator weed.
Each boat goes to a designated location where the vivacious beetles have been scouted out previously feasting on the alligator weed.
There's a small craft operator and a collector on each airboat when they reach the mat of alligator weed. The collector stands on the bow of the airboat as it slowly plows through the invasive plants. The disturbance of the craft moving through the green carpet sends thousands upon thousands of little flea beetles flying through the air. The nimble collectors sweep the net back and forth, catching the beetles in the cloth net. When enough beetles are collected, they are placed in cups with some alligator weed and placed into the cooler.
Bohaty says, "We can typically collect anywhere from 10,000 to 50,000 beetles a day."
So where do all these beetles go? They get shipped to Louisiana, Alabama, Arkansas, and as far north as North Carolina to our partners: state and federal agencies, Corps districts, universities, and the U.S. Army Engineering Research and Development team (ERDC).
These partnerships not only study the alligator weed but the beetle as well. ERDC serves as a nucleus of knowledge for districts.
"We have a valuable resource here at ERDC. We have genetic diversity of all the alligator weed that is present in the U.S.," explains Harms. "And it lets us address questions about how the flea beetles might work and how they might control alligator weed given its introduction into different parts of the country."
Jacksonville, Florida has the right climate to sustain the reproduction of the flea beetles. It is the perfect place to monitor the effects of generations of biocontrol and the ideal place to collect new beetles, in order send them to places like the Little Rock District in Arkansas where the alligator weed is aggressively taking over.
At the U.S. Army Corps of Engineers, Little Rock District, biologists like Cherrie Lee Phillip take the beetles back out into the waters of Arkansas. Using an airboat, they collect alligator weed samples, demark areas to observe both the alligator weed and the beetle and place the hungry beetles onto a mat of alligator weed.
"When we get beetles, [there are] 250 beetles per cup, and that one cup will cover one acre of the alligator weed," says Phillip. "Here at Millwood Lake, we have approximately a thousand acres (of alligator weed), but that varies year to year depending on the temperature."
The cooperation between the district and ERDC is just one of the many collaborative efforts that the Corps participates in to help to advance the study of the aquatic invasive itself. There are many research questions that ERDC strives to answer: How does the plant evolve and once introduced how does it spread into an area? The study also aids with finding the most efficient and sustainable ways to use the alligator weed flea beetle, especially when colder climates and plant variations become a factor.
The Corps is continuously evolving to combat the challenges of the invasive species problem. We embrace the philosophy of early detection and rapid response, and finding the best strategies with the least amount of environmental impact.
We understand that complete eradication of an invasive species may not be possible. But by using the Corps collective knowledge, we can employ the best methods to manage the aggressive nonnative species to keep them at the lowest feasible levels to reduce their negative impacts on native ecosystems and our economy.