By Allison Vincent
Have you ever been out on the trail, any trail, and that friend that knows a thing or two about invasive species points out a few for you? He or she discusses the threat they pose to the native ecosystem that they’re encroaching on and you wonder, what can we do about it?
One highly successful way of managing invasive species is to employ a biological control agent, using other living organisms to help control invasive and non-native species. It’s a way of reacquainting invasive pests – such as Old World Climbing Fern or Lygodium microphyllum – with their natural enemies to provide natural and sustained population reduction. In the case of Lygodium, the enemy is the brown Lygodium moth (Neomusotima conspurcatalis) which has been successfully used in Florida since 2008.
It’s time-consuming and difficult to get official approval to use biological control agents, but it’s worth the wait. Some agents have proven to be very successful and without unintended consequences. Biological treatment studies often extend for decades before hitting the ground, assuring that there are no negative impacts beyond their intended use.
You may have noticed technicians at the CREW Bird Rookery Swamp trails lately distributing state-approved biological control agents near pockets of a certain species. They hope to limit the expansion of Lygodium from the area – a tall order, as it is one of the worst invasive species, crowding out many native plants and habitats for wildlife. Management of this invasive plant using traditional strategies, such as mechanical and chemical treatments, has proved difficult and expensive, with limited long-term success. Enter biological control agents.
Without natural competition, invasive plants like Lygodium will inevitably wreak havoc on an area not ready for its intense growing cycle. Each fertile leaflet has 133 sori – or the frilly bits on the fern – and each sori has 215 spores! Multiply those numbers to find that each fertile-female leaflet may spread 28,500 spores into the surrounding area (Volin et. al, 2004). It doesn’t stretch the imagination to picture the fern-filled scene should the invasion go untreated. Every invasive plant spreads through different means and in the case of Lygodium, the female portion of the plant with her fertile spores does the work. Other common invasive plants, like Caesar weed, spread by other vectors, such as wildlife and humans. Caesar weed has a particularly sticky bur containing lots of seeds, so be sure to trash those burs that make it home with you after a hike.
But how do the land managers, the South Florida Water Management District (SFWMD) in the case of CREW, go about treating such a powerful invasive plant? Well, they fight fire with fire, sometimes literally, as prescribed fires, after other biological and chemical treatments, have been known to increase the successful die-back – or sustained control of plant spread – both above and below the ground. Many times land management uses a combination of mechanical, chemical and biological control to yield the best results.
In the case of Lygodium, the biggest observable impact in the long-term comes primarily from biological control and, in particular, those brown Lygodium moths. While other species have been introduced and had some success in destroying Lygodium, the brown Lygodium moth has unleashed the biggest disaster for this invasive plant.
It all starts with little caterpillars, who feed on fern leaflets causing browning of leaves and breakdown of entire Lygodium plants. Female moths lay an average of 136 eggs during her short life span – the life cycle of the moth from egg, through caterpillar and pupa to adult, is only about 30 days. Researchers observing the impact of testing sites over 4-6 months found that moth populations increased, and noticeable caterpillar feeding damage in the form of browned-out patches of Lygodium became apparent. Good for us, bad for Lygodium.
Throughout the history of CREW, biological control agents have been used as one element of a three-part approach to treat the invasive Melaleuca quinquenervia tree on the CREW lands. You can still see the process in action in the “Melaleuca graveyard” on the Red trail of CREW Flint Pen Strand where large stands of trees were treated with a combination of mechanical and chemical treatment. Later, biological control agents were added for long-term success – if you look closely you can still see weevils and psyllids, the Melaleuca-loving biological control agent.
We all benefit from the long-term research studies on biological control agents. Through partnerships with leading wildlife agencies and the SFWMD, land managers for the CREW lands hope to see similar results, like the sustained success on throughout the state. There will always be a need for invasive treatment, but with each step we take toward restoring our natural Florida environment, everyone benefits.