MELALEUCA a prolific seed producer

MELALEUCA, a prolific seed producer

Unwelcome visitors: Biological control for invasive pests

• The latest example is the release of beneficial beetles to target air potato vine, an “aggressive, invasive exotic plant that is displacing native plant species and disrupting ecological functions throughout Florida,” according to the USDA-ARS.

Researchers at the Invasive PlantResearchLaboratory in Ft. Lauderdale, Fla., are busy trying to find biocontrol options for invasive species that threaten native plants.

The latest example is the release of beneficial beetles to target air potato vine, an “aggressive, invasive exotic plant that is displacing native plant species and disrupting ecological functions throughout Florida,” according to the USDA-ARS.

Broward County students were “invited to participate in the beetle release to stimulate their interest in nature and biology, and to provide them with a deeper understanding of biological control and its benefit to the environment.”

Ted Center, research leader at the lab (, spoke with Farm Press about the facility’s history, goals and current work. Among his comments:

The Invasive Plant Research Laboratory’s (IPRL) history…

“We were originally called the Aquatic Plant Control Research and released the first biocontrol agent on alligatorweed in 1962. That preceded my arrival here in 1971.

“We’ve since worked on multiple projects, with most of our focus through the years on aquatic weeds — water hyacinth, hydrilla, alligatorweed, water lettuce, giant salvinia.

“In the 1980s, we began work on an Everglades invader, melaleuca, a large tree from Australia. That’s probably the largest plant ever targeted for biocontrol, and it was a really successful project.

“Since then, we’ve taken on other Everglades invaders, including Brazilian pepper, climbing fern, and now air potato.

“We’ve developed and released 21 or 22 biocontrol agents over the past 50 years. It’s kind of a slow process — we get one out every couple of years.

“Our research involves all aspects of biocontrol. We start working with land-management agencies in choosing targets. Then, we must figure out where the invasives came from. Many times, that involves a lot of foreign travel.

“We do molecular matching to determine if the genotype of the test plant here matches the one from overseas. We then do surveys overseas to identify potential biocontrol agents and cooperate heavily with overseas laboratories. There are labs in Australia and Argentina that we cooperate with a lot. Other collaborators are in China, Thailand, Nepal, and Africa.

Pre-screening work

“Working with all these groups, we normally do pre-screening before we ever bring the insects over to the U.S. Once we find an insect that shows promise — that proves to be a specialist on the target — we bring them here to the lab and study them in quarantine.

“In the past, all our quarantine work has been done in a small facility located at Gainesville, next to the University of Florida. But since 2005, we’ve had our own quarantine facility here at Fort Lauderdale. It’s a state-of-the-art facility and is designed to insure that insects can’t escape. This allows us to study them without having to work overseas.

“Once we have the agent tested, there is a long process to receive regulatory approval to release it. Once a permit is secured, we put it in the field and do studies to confirm that it is host-specific, effective, how well it disperses and other things.”

More on melaleuca…

“Melaleuca is an interesting plant that is really adapted to fire conditions. As a result, it produces seeds that are in persistent capsules that stay up in the canopy of the tree until something causes them to dry out. Then, they release the seeds en masse. One small tree can have 10 million seeds on it.

“In the past, to control it, they’ve used herbicides or cut the trees. That, in turn, causes the branches to desiccate and drop seeds. So, where once there was a single tree, all of a sudden there can be an acre of seedlings coming up. It’s a management nightmare.

“As part of our biocontrol strategy, we wanted to find agents that would reduce seed production. The biology of the plant is such that the seeds are produced on the growing tips. A shoot will grow, produce leaves and flowers, and continue that pattern over and over.

“The insects we brought in are very effective at attacking the tips of the branches and stopping the growth process. As a result, we’ve seen seed production drop by 90 percent to 95 percent.

“The first insect we released was a weevil, a top-feeder. The second was a psyllid, a small insect similar to an aphid that feeds mainly on the young foliage at the tips.

“The third insect — actually an insect/nematode combination — is gall-former. A gall causes an abnormal growth in a plant that is almost like a barnacle. The plant puts all of its resources into this gall, a gnarly, woody growth and then doesn’t have the materials needed to continue to grow.

Followed up with midge

“However, that one failed, and we followed up with a midge, which looks like a mosquito. It lays its eggs in the growing tips and produces stem galls. That one has been extremely effective.

“Between that combination of insects, we’ve cut way back on seed production. If it does produce seed and they germinate, many of the insects will attack those young seedlings. If the seedlings manage to survive, the insects stunt their growth so they can’t go anywhere.

“It has proven to be a very effective project — but only when integrated with the other management practices. The insects don’t remove the trees and there’s all this wood out there that must be taken out. But the biocontrol program has made that process much more effective.”

The air potato vine…

“Air potato vine is one of the things we’ve been working on recently and it’s the latest biocontrol agent we’ve released. Our first release was in cages last fall. The first open release was last March.

“Air potato is a lot like kudzu — it grows over the tops of trees and blankets everything. It cuts down on light, kills the understory and is particularly bad in conservation areas.

“In the spring, it sprouts from things that look like small potatoes. Those produce vines that can grow eight inches per day. They go straight up whatever vertical surfaces are available.

“During the summer, they usually overtop trees and then, in November, they’ll die back. As they die back they pump their resources into more of the potato-like structures (also known as ‘baubles’). Those will then drop to the ground and the next fall they’ll sprout and begin the process all over again.

“We’re working with two insects — both leaf beetle types — to deal with this plant. One leaf beetle feeds on the vine itself and defoliates it. That cuts down on the resources the plant has to produce baubles. We’re hoping the bauble production will really drop off after we release them.

Check on safety

“The second leaf beetle feeds on the baubles. That is currently in quarantine and being studied to see if it’s safe to release.”

Doing no harm…

“We want to make sure any insects released don’t attack any valuable plants or crops.

“Many people don’t stop and think about this. But, say, you have a garden and an insect is attacking your string beans. Typically, that same insect won’t feed on your corn. By their nature, most insects tend to be specialized on certain plant species. A few, like gypsy moth, feed on just about everything.

“So, we want to make sure we find insects that are specialists and not generalists. That’s why we spend two or three years simply testing these insects in quarantine and overseas to insure that is the case. We don’t want surprises.”

Has the United States sent invasives to other countries? Has the traffic gone the other way, as well?

“Absolutely. In fact, we go to Australia to find biocontrol agents of our Australian weeds. At the same time, Australians come here looking for biocontrol of their North American weeds. There’s a lot of sharing.

“Many of the weeds — particularly rangeland weeds — were contaminates in seed stock. But most of the ones we deal with in south Florida come from the nursery trade.”

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