Linda Benedict, Bogren, Richard C.
Rick Bogren and Linda Foster Benedict
Because invasive, non-native plants and animals can cause havoc, Louisiana Agricultural Experiment Station scientists conduct research programs to bring these problems under control. Two that present particular challenges – especially in urban areas – are red imported fire ants and Formosan subterranean termites.
Red imported fire ants
Red imported fire ants have troubled people, pets and livestock since their introduction into the United States in the 1930s. They were accidentally brought here from South America, where they are held in check by competing organisms and environmental factors. That’s not the case in the United States.
In Louisiana, entomologist L.D. Newsom and others raised the issue of ineffectiveness and environmental consequences of wide-area application of heptachlor in the 1950s. LSU AgCenter scientists began research efforts on fire ant control in urban areas in 1999. Their focus was the use of baits that have low doses of insecticides. In the case of ants, workers find the bait and carry it back to the colony, where it is fed to the larvae, other workers and queens, thus killing the colony.
A new research focus is biological control with natural enemies. One of these is the phorid fly. These tiny flies, which are less than 1.5 millimeters in length, are known as decapitating flies. They attack fire ants exclusively. The female fly lays a single egg in the thorax of a worker ant. When the egg hatches, the maggot moves into the head and consumes the contents, causing the head to fall off.
The first successful release of the phorid fly in the United States was by the U.S. Department of Agriculture in Florida in 1997. The first successful release by LSU AgCenter scientists was in 1999 followed by releases around the state from 1999-2006. All the releases were in pastures. In a follow-up study in 2009, AgCenter scientists found one of the two types of phorid flies released remaining in 46 out of 64 parishes and the other type still surviving in 57 of the 64 parishes. It is expected that the reduction in fire ant populations will help mitigate their negative effects on humans, livestock and wildlife.
Despite the problems they cause, fire ants also provide numerous benefits as predators of agricultural pests. For example, researchers have documented a major decline in tick populations as fire ant numbers have increased. The researchers found that dragging pastures with a metal harrow during winter significantly reduced the number and size of fire ant mounds for up to 15 months. The result was fewer fire ant problems in cattle while at the same time maintaining ant populations that countered the ticks.
Red imported fire ants are a natural deterrent to the sugarcane borer in sugarcane fields and help hold down the numbers of these pests, which can cause yield losses for sugarcane farmers. New research is showing that these ants are also a natural enemy of the Mexican rice borer, which is a new invasive species in Louisiana threatening both sugarcane and rice.
A recent AgCenter study shows that fire ants trapped under water escape by lifting themselves to the water surface using bubbles collected at the water’s bottom. Fire ants have hairs that naturally hold air the researchers call “native bubbles” – smaller than the bubbles in a glass of champagne – that give them buoyancy. The study showed the ants have developed a defense mechanism by gathering together and intertwining themselves into floating conglomerations the researchers call “rafts.” A raft is made up of worker ants that surround the queens and brood – eggs and larvae. While the brood holds bubbles, worker ants rotate through the raft keeping it in motion so it won’t sink.
Formosan subterranean termites
Another invasive species that has been the target of Louisiana Agricultural Experiment Station research is the Formosan subterranean termite. Introduced to the United States in the 1940s in military equipment coming back into the country from the South Pacific following World War II, Formosan subterranean termites have had devastating effects in New Orleans, Lake Charles, Baton Rouge and Monroe.
AgCenter entomologist Bill Spink recorded the first Formosan subterranean termite infestation in the continental United States in a Texas shipyard in 1965. The next year he discovered large infestations around the Naval Training Center, Todd Shipyard and Camp Leroy Johnson in New Orleans.
In 1989, AgCenter entomologist Jeffery LaFage oversaw the first collection of swarming, winged termites – alates – in the French Quarter, finding an average of 502 adult insects per trap. LaFage was killed in a French Quarter robbery in July 1989, only months after that first survey was completed.
Ten years after LaFage’s death, a termite control program was initiated in the French Quarter called Operation Full Stop. The LSU AgCenter worked with two other agencies to implement this program – the U.S. Department of Agriculture and the New Orleans Mosquito and Termite Control Board. The program began in a 16-block section and expanded into a wider area before it was curtailed because of a loss of funding in 2011.
Inspections of properties in 2003 found 26 percent of the buildings were infested with live termites, and inspections in 2005 showed 5 percent of the buildings infested.
Formosan subterranean termites expand their territories by producing winged “alates” that swarm each spring. Alate numbers were sampled using sticky traps placed on light poles. In-ground monitoring stations were installed in holes drilled through the sidewalks throughout the French Quarter. Using genetic analyses, researchers have shown the number of mature colonies has been reduced. DNA profiling identifies hereditary factors visible as a specific banding pattern – or fingerprint – of each individual and each colony. Using this information, researchers showed that the number of colonies contributing to swarms caught in traps dropped from an average of 13 in 2003 to seven in 2007 and only two per trap in 2008.
Although termites feed on wood and other cellulose products, they depend on bacteria in their digestive tracts, or gut, to digest the wood fibers and get the nutrients they need. AgCenter researchers have come up with a way of transferring genetically modified bacteria into termite populations. The researchers want to engineer bacteria found exclusively in the termites’ gut to produce substances toxic only to Formosan subterranean termites, which don’t have natural enemies in the United States. Bacteria naturally multiply as they’re passed around a colony. Like a “Trojan horse,” the bacteria can intro introduce and spread a killer gene throughout a termite colony.
AgCenter scientists have studied toxicants that do not repel termites. These nonrepellent toxicants act like baits, but the transfer is through touching rather than feeding. Contact toxicants can be more effective than baits because termites spend more time grooming each other than feeding each other.
The potential of vetiver grass as a termiticide was identified by a nursery and greenhouse operator in Metairie. The operator thought he might be on to something when he noticed a lack of bugs in greenhouses where he was growing vetiver. He took his idea to the LSU AgCenter. AgCenter scientists extracted oils from the roots and discovered they contain a chemical called nootkatone, which is both a repellent and toxic to termites. A study to evaluate nootkatone showed that a 25 percent vetiver-root mulch treatment decreased tunneling activity and wood consumption and increased termite mortality.
Read an article by Gregg Henderson, entomology researcher, on Educating four generation of pest control operators.
Rick Bogren, Professor, Communications, Professor, LSU AgCenter, Baton Rouge, La. and Linda Foster Benedict, Associate Director & Professor, Communications, LSU AgCenter, Baton Rouge, La.
(This article was published in the spring 2012 issue of Louisiana Agriculture.)