The Tennessee Division of Natural Areas Assists Australia in Biological Control Research
The Division of Natural Areas, Natural Heritage Program considers the aquatic plant Delta Arrowhead (Sagittaria platyphylla) a Species of Concern in Tennessee. According to the University of Tennessee Herbarium, the plant has been recorded in only eight Tennessee counties. In west Tennessee, it can be found at Reelfoot Lake in Lake and Obion Counties and Sunk Lake State Natural Area in Lauderdale County. Here, the plant can be found growing along the lake edges, within ditches, and in wet fields.
According to the online NatureServe database, delta arrowhead is known to occur in 16 states ranging from the southeast north to Ohio and west to Texas. Within this range, seven states rank it as critically imperiled, one state (Tennessee) ranks it as imperiled and the remaining states have not yet ranked the plant's status.
For such a rare plant it would seem paradoxical that it would be a problem weed anywhere. But this is the case in Australia where the plant is considered a noxious aquatic weed. It was first identified in Australia in 1959 near Brisbane. Since its initial occurrence, it has spread across most of Australia and has the potential to spread even further.
In Australia, delta arrowhead forms dense and widespread colonies in drains and channels. These dense stands cause decreases in the efficiency of crop irrigation which leads to production losses and increased irrigation costs. The plant has negative impacts to recreational activities primarily fishing and boating. It threatens native aquatic flora and fauna by competing with natives which eventually leads to reduced plant biodiversity. Control and eradication of the plant by mechanical and chemical methods is costly and labor intensive and has a low success rate. A new and better way to control this plant is sought after by the Australian authorities. One method that is being considered is biological control- the use of other organisms to control pest species.
I first met Dr. Raelene Kwong on August 16, 2010. Dr. Kwong is a Senior Research Scientist with Australia's Department of Primary Industries. I assisted Dr. Kwong and Jean-Louis Sagliocco (also with the Department of Primary Industries) in locating delta arrowhead at Sunk Lake State Natural Area and the following day along Bayou du Chien at Reelfoot Lake. Because the Division of Natural Areas keeps mapped records of rare Tennessee plants, we were able to go directly to known populations. Once at a population, insects feeding on the plants were collected as were a sample of the plants.
Dr. Kwong is interested in comparing the genetics of the North American delta arrowheads with populations in Australia. In turns out that the delta arrowheads in Tennessee are most similar genetically to the plants in Australia. This information shows that it is highly likely that the source of delta arrowhead in Australia originally came from Tennessee. Arrowheads most likely were shipped to Australia for nursery stock. Delta arrowhead is sometimes planted in wetland gardens.
She was also interested in the insects feeding on our arrowheads. Four species of weevils all in the genus Listronotus were collected. The most common and abundant weevil encountered was L. appendiculatus. Adults of this species feed on flowers and fruits. Their larva feed in the fruits where they cause significant destruction to the receptacle and developing seeds. Though this weevil was not the only target for biological control of delta arrowhead in Australia, it became a focus species.
I assisted the research again in 2015 and 2016 by collecting L. appendiculatus from delta arrowheads at Sunk Lake and Reelfoot Lake. 2015 was not a good year for weevils; I only collected 20 weevils despite looking at 100s of arrowhead flowers. 2016 was a different story- I collected 58 weevils. All my weevils were mailed alive to researchers in the United States. They were interested in finding out what other plants besides delta arrowhead the weevils would feed on. This is imperative research since these weevils may be released in Australia. If they also fed on native arrowheads in Australia, that would cause yet another conservation problem.
Dr. Kwong and Australian biologist Franz Mahi visited Tennessee in September of 2015. I assisted them in collecting weevils on Sagittaria latifolia, a common arrowhead in Tennessee at Ghost River State Natural Area. They also collected at Sunk Lake and Reelfoot Lake. They returned at in September 2016 along with Australian biologist Jackie Steel to collect larval weevils for identification.
Biological control of an exotic species can be risky. The control species may end up not actually controlling the exotic or it may end up harming a non-targeted species. When it does work, the benefits can be significant (ex. Weevils released in Lake Victoria have reduced the invasive exotic water hyacinth by 85%. The same weevil has had great success in controlling hyacinth in the United States). Intensive research before releasing an exotic biological control agent is necessary in avoiding negative results.
If all goes well, the Tennessee weevils may someday end up controlling delta arrowhead in Australia. The benefits to Australia's economy and ecology may be significant.
It was with great honor to have the privilege to work with the Australian biologists on this project. As a TDEC employee, you never know where your job will take you. The information on delta arrowhead populations provided by the Division of Natural Areas was important in making this research a success.