Natalie A. Hummel, Krishna Paudel, Craig Roussel, Tad Hardy and William Spitzer
Louisiana is a beautiful state with a unique blend of cultures and habitats. Positioned on the Gulf of Mexico and at the mouth of the Mississippi River, the state benefits economically from international trade and interstate commerce. Unfortunately, these factors also make the state vulnerable to invasive species introductions. The spread of invasive species threatens economic and ecological stability by decreasing biodiversity, displacing native species and increasing agricultural production costs.
For this issue of Louisiana Agriculture, we define invasive species as any non-native species that has entered and spread aggressively causing damage to agricultural production, human habitation, forestland, wetlands or native species. Although not all non-native species are invasive, those that are cause an estimated $120 billion in damage in the United States each year. In a 2009 U.S. Department of Agriculture report ranking the relative risk exotic pests pose to the 50 states, Louisiana was ranked ninth. Within the past 12 years alone, 33 new invasive plant pest species have been detected in Louisiana. Realizing the threats to the Louisiana economy and ecosystem, LSU AgCenter scientists conduct research and extension programs aimed at prevention, control and eradication of invasive species.
The economic impact of invasive species is difficult to calculate but is significant. The damage caused by the Formosan subterranean termite, for ex ample, is estimated to exceed $1 billion per year in the United States with the portion accrued in Louisiana alone exceeding $500 million per year. AgCenter economists have completed an extensive cost analysis of control choice options in Louisiana. For the past 20 years, AgCenter researchers have used traps to monitor Formosan termite populations in the French Quarter and greater New Orleans area. Within the past few years, AgCenter researchers have begun using DNA profiling to monitor individual colonies, which are genetically distinct from each other. The data generated by monitoring through trapping and DNA techniques have been used to garner federal funding for a project known as Operation Full Stop. Because of this project, Formosan termite numbers in New Orleans have been significantly reduced.
Another economically important invasive species – the red imported fire ant – was discovered in Louisiana in the 1950s. These ants infest lawns and pastures and can attack humans and live stock resulting in death in some cases. AgCenter researchers are developing sustainable control methods. One such approach is the release of parasitic flies as a biological control agent, which is proving to reduce populations of fire ants to manageable levels.
Recently, the stability of the citrus fruit and nursery tree production industries has been threatened by the introduction of many invasive insects and diseases. The value of the Louisiana citrus industry is estimated at $10 million annually. AgCenter scientists have worked with state and federal agencies to rapidly respond to these detections. They have developed educational materials and provided management recommendations in response to invasive species detections. Without these interventions, Louisiana’s citrus industry could face extinction.
The sugarcane and rice industries are under threat of infestation by the Mexican rice borer. Once established, this pest may cost Louisiana sugarcane producers $220 million and rice producers $45 million in the first few years. AgCenter scientists have been working cooperatively with Texas scientists to stem the movement of the borer and buy time to develop effective management and control methods. This cooperative program resulted in early detection of this pest in December 2008 by Louisiana Department of Agriculture and Forestry (LDAF) specialists.
Animal species that have invaded Louisiana include the feral hog, which has recently begun to cause major damage to agricultural and forestland. Nationwide, the damage is believed to exceed $1.5 billion annually. In 2008, AgCenter and LDAF scientists surveyed landowners to obtain an estimate of the severity of feral hog infestations. Eighty percent of survey respondents in 50 parishes reported the presence of feral hogs with 95 percent reporting damage to property, crops or forests. AgCenter scientists also have measured the impact of feral hogs in aquatic environments and have found that they are responsible for introducing significant levels of biological contaminants into freshwater supplies.
Another animal invader is the nutria, which causes damage to Louisiana’s marshland. The most effective method for management of this pest is trapping for fur and consumption. Demand for fur has declined significantly in the past 50 years, and Louisiana has an aggressive campaign to encourage consumption of nutria meat.
The waterways of Louisiana are threatened by the Asian carp. This fish causes harm not only to the environment and other fish, but also injury to property and people with its tendency to leap from the water and hit boats.
As soon as an invasive species is discovered, the LSU AgCenter works closely with state and federal regulatory agencies. As a rule, port inspection authority for invasive pests lies with the federal government through the USDA Animal and Plant Health Inspection Service (APHIS). State activities are accomplished by LDAF Plant Quarantine Programs. The AgCenter supports regulatory efforts through education programs
The response to discovery of an invasive species involves prevention and preparedness. Strategies for prevention include monitoring and control activities carried out in foreign countries, at U.S. ports of entry and within the United States. The USDA inspects imported shipments and monitors for federal pests of concern. LDAF conducts pest surveys and inspections on many commodities statewide, facilitating early pest detection and pest-free certification for export to other states or countries. Commodities may include nursery stock, grains, citrus, sweet potatoes, sugarcane, honeybees and forest products. Agricultural equipment also may be included.
One important prevention strategy is an analysis of the characteristics of the plant or animal species to develop a cost-sensitive decision support tool. The decision support tool helps to identify effective control strategies against introduced invasive species. LSU AgCenter faculty assist regulatory agencies when they are developing these tools.
Preparation activities may include development of a risk analysis to assess loss or injury to a crop or ecosystem. An invasive pest not only causes crop damage, but can affect commodity markets, human health, food safety and the environment. For example, financial markets worldwide may be adversely affected with the introduction of a new pest into a major commodity such as rice.
State response to invasive species may be separated into two categories, routine and targeted. Routine response consists of ongoing surveillance at sites with regulated materials, such as plant nurseries. The goal of routine survey is early detection of pest problems and safeguarding of agricultural products. Discovery of an invasive species during routine surveys may trigger stop- sales, treatments, return to origin or destruction. In some cases, sites may need follow-up inspection or remediation. LSU AgCenter scientists develop educational materials featuring the species being monitored.
Targeted response also requires action tailored to the invasive organism. The goal of targeted response is to prevent the spread, reduce harm, and manage or eradicate the problem. The annual tropical soda apple weed survey, for example, relies on visual survey of pastures and rodeo arenas with subsequent property restrictions and herbicide treatments when the weed is found. Cattle cannot re-enter until fruiting plants are eliminated. Cactus moth – a federally-regulated pest – is monitored using pheromone trapping and visual survey for the prickly pear host. Teams of inspectors across Louisiana coastal lands search for moth-infested cactus. When found, the cactus is destroyed. Moth locations are tracked with GPS, and teams map their progress. When the pink hibiscus mealybug was found in southeastern Louisiana, LDAF conducted surveys to determine how widespread this ornamental pest was in residential settings. Parasitoid wasps for biological control were released weekly. Sentinel sites still monitored confirm a high success rate of this control program, which helps prevent spread to major agricultural crops in Louisiana. Giant salvinia weed management is another biocontrol success story in Louisiana, using natural organisms to recover from invasive pest damage.
Pest mitigation measures may be straightforward, such as conducting surveys and inspections or applying treatments. Others may require restrictions on high-risk plants. Quarantines represent the most restrictive response and are enforced on pests with high impact potential. Strategies may be devised using multiple mitigation methods. Regulatory response should be reasonable, uniform, science-based, transparent and limited in scope so that benefits outweigh risks.
In some cases the risk posed by an invasive species is so great that attempts are made to eradicate it. Eradication is difficult and costly and effective only if initiated immediately after the first detection. It may require one or a combination of methods such as chemical, mechanical, vaccination or even release of sterile males into the ecosystem. An eradication effort may not be successful, such as the failed attempt to eliminate fire ants in the South. Furthermore, eradication of invasive species may result in secondary effects such as emergence of a new species that may dominate the ecosystem.
In a few cases, however, eradication can be successful and worth the investment. Examples of successful eradication programs in Louisiana include the pink bollworm, sudden oak death and southern bacterial wilt disease. The financial investment to prevent the spread of these invasive species has decreased the long-term cost to industry.
The Boll Weevil Eradication Program represents the ultimate targeted response: a cooperative, long-term strategy to eliminate an organism through survey, treatment, quarantine and maintenance. The cotton boll weevil first appeared in Louisiana in 1903. Boll weevil damage to developing cotton bolls was a major yield-limiting factor in cotton production in Louisiana. Nationally, the boll weevil is estimated to have cost cotton farmers more than $15 billion in yield loss and additional costs to control the pest. An eradication program was initiated in Louisiana in 1997, and since then approximately $167 million has been spent on boll weevil eradication ($77.6 million by the state, $25 million by USDA, $64.3 million by the cotton growers) in a unified eradication program. In 2010, one weevil was trapped in the third week of May in Louisiana. At this time there is no evidence of boll weevil reproduction in Louisiana.
Ultimately, management of invasive species through containment or control may be the only way to overcome economic and environmental damages. In containment, an effort is made to confine the invasive species within a limited geographical area. Control aims at keeping invasive species below a certain threshold level – a level in which economic and environmental cost can be tolerated.
We hope you find this issue of Louisiana Agriculture helpful. Please do not hesitate to contact any of the authors of these articles for more information about invasive species.
For a table of invasive species and the impacts and response actions in Louisiana from 1998 through 2010, go to Invasive Species.
Natalie A. Hummel, Assistant Professor, Department of Entomology, LSU AgCenter, Baton Rouge, La.; Krishna Paudel, Associate Professor, Department of Agricultural Economics & Agribusiness, LSU AgCenter, Baton Rouge, La.; Craig Roussel and Tad Hardy, Louisiana Department of Agriculture and Forestry; William Spitzer, U.S. Department of Agriculture, Animal Plant Health Inspection Service, Baton Rouge, La.
(This article was published in the fall 2010 issue of Louisiana Agriculture.)