Preventing Invaders

Contact: James Young, Plant Protection and Quarantine, USDA APHIS |
Matt Travis, MD State Plant Health Director, USDA APHIS |

Hundreds of Cargo Containers full of products and possible pests. (Photo USDA APHIS R. A. Eaglin)
Souvenir with Borer damage from Passenger Baggage (Photo: USDA)

ANNAPOLIS, MD (December 1, 2015) – Exotic species are in the news almost daily. They can be found in our parks and even in our own backyards. Sadly, many of them are so common, most people do not realize that they do not belong here. To be invasive, an organism must have evolved somewhere other than where it's found in Maryland, have a negative impact on the environment it moves into, and have been moved, deliberately or by accident, by people.

For example, when the brown marmorated stink bug silently slipped into the U.S., it was years before it was correctly identified as an exotic species. By that time it was already becoming a pest in orchards and vineyards.

One of the first questions about most invasive species is "How did it get here?" — quickly followed by "Could it have been prevented?" The majority of invasive plant seed, disease and insect pests are accidentally introduced. How, you might ask? While the list of pathways is surprisingly long, the most common avenues are the movement of goods produced in foreign countries, travelers returning home with souvenirs, and internet sales. The U.S. Department of Agriculture (USDA) and Customs and Border Protection (CBP) work to prevent the introduction of such pests. In this month of increased holiday travel by both people and packages, the Maryland Invasive Species Council has chosen this prevention work as the topic for the December's "Invader of the Month".

Cargo is moved in large containers with products shrink-wrapped on pallets, in boxes, or simply loaded in trucks. This results in many small hiding places that insects, seeds, and snails can use to move, unbeknownst to them, all over the world. To prevent this from happening, CBP, a branch of the Department of Homeland Security, routinely inspects cargo. The searches are extensive and include examining the exterior of shipping containers for hitchhikers adhering to the undercarriage and walls. Inside the container, pallets are checked to ensure that they have been properly treated to prevent the movement of bark beetles and woodborers. Inspectors then move to the product being shipped. Flashlights, forceps and box-cutters are routinely used to open, inspect, and manipulate the products to ensure they are pest free. The final stage of an inspection is to sweep out the empty cargo container and look for any seeds or insects that were hiding in the corners.

Most people love escaping on vacation, but if you have ever traveled internationally you might recall filling out a declaration form before leaving the faraway airport to return home. Preventing the movement of pests in baggage is challenging and relies on several factors, including the declaration form. The declaration is a reminder to all passengers entering the US that bringing in certain items is prohibited. The declaration is a federal form and false claims are subject to penalty. To reinforce the urgency and in an attempt to keep people honest, CPB randomly selects passengers for screening, checks passenger lists against a database of previous violators, and walks the baggage floor with highly trained K9 units.

The last pathway of pest introduction is internet sales. The internet has drastically increased the average person's ability to buy products, knowingly or not, from foreign countries. Foreign markets are trying to meet the high demand for heirlooms and specialty varieties and non-GMO seeds for home gardeners. Small packets of seeds are easily mailed and are found only by hard work and highly trained K9 Units. Unfortunately, a recent study reports that our current biosecurity practices are not effectively preventing the trade of plant material via internet sales (Humair et al. 2015).

CBP officer inspecting packages for prohibited items (Photo: CBP James Tourtellotte)

You can contribute to the economic and ecological safety of the US and your own backyard by being a careful and conscientious traveler and internet purchaser. Know what you're importing, where it comes from, and make sure it's legal.Given the sheer volume of cargo, baggage and mail entering the US on a daily basis, it is unrealistic to believe that every pest will be found. Pests such as the tomato leaf miner (Tuta absoluta), wheat bug (Nysius huttoni), oak ambrosia beetle (Platypus quercivorus) and Asiatic brown rot (Monilia polystroma) are known threats. Unfortunately there are hundreds of species like them that not only threaten our neighborhoods but the entire U.S. economy. In response to this ongoing threat, the US Department of Agriculture (USDA) has established several programs to eradicate, or at least mediate the impacts of, new pests. Examples of this work include recalling products found to be infested or in violation of federal regulations, conducting surveys in and around the ports where cargo first enters the US and pests are most likely to establish, and providing funding to perform trapping across the country for high risk pests.

For more information about Invasive Species of Concern in Maryland, visit the Maryland Invasive Species Council.

photos available electronically on request.


Humair, Franziska, Luc Humair, Fabian Kuhn and Christoph Kueffer. 2015. E-commerce trade in invasive plants. Conserv. Bio. (in press)

US Department of Homeland Security, U.S. Customs and Border Protection. CBP Form 6059B (04/14)

Additional Resources

Animal and Plant Health Inspection Service