Monday, July 26, 2021

German snails and lots of steam: WSDA embraces innovation to respond to another invasive threat

Karla Salp

vineyard snail
Vineyard snail
The recent interception of giant African snails at a Texas airport alerted many Americans to the fact that invasive snails can pose a serious threat to the country, but WSDA has long known about this threat and has actively worked to eradicate an invasive snail detection of our own. 

The invasive snail is Cernuella virgata but most people just call it the vineyard snail. The snails pose a threat to agriculture by directly attacking crops – such as wheat – and also clogging up machinery when farmers try to harvest their crops. 

And while most people think of steaming snails as more of a culinary endeavor, WSDA’s Pest Program is gearing up to use steam treatments to eradicate invasive snails at the Port of Tacoma late this summer. 

The vineyard snail was first detected at the Port of Tacoma in2005 and WSDA has been working to eradicate the population since 2007. The project has been a collaboration between WSDA, the Port of Tacoma, and Washington State University (WSU). The initial infested area was approximately 300 acres but now has been reduced to less than one acre on a single property.  The last acre has proven to be a real challenge, as it is classified as a wetland and traditional treatment methods are not available.  The hope now is to complete the eradication using experimental steam treatments – a potential alternative to pesticide-containing snail baits.  

A snail-steaming solution

two people lifting a plastic sheet with steam coming out
Snail steam trial at Port of Tacoma
Steam-killing snails in the ground is easier said than done. WSDA and WSU have been fine-tuning the method over the past two years. To kill the snails at infested sites, steam hoses are snaked over an area and covered with plastic to hold in the heat and moisture. Steam is pumped through the pipes for several hours to bring the temperature of the first six inches of the soil up to at least 56 degrees Celsius for a minimum of 30 minutes. 

Part of the challenge, though, is identifying which snails are native and which are invasive. Vineyard snail looks very similar to some native snails, and it takes a trained eye to spot the difference.  Even then, it can be tricky. To help positively identify the invasive snails, WSDA has turned to DNA to provide greater certainty. 

DNA – stopping invasive species in their tracks 

WSDA’s molecular diagnostics laboratory in Olympia has been a game-changer in the Pest Program’s ability to respond to pest issues. Rather than having to wait days or weeks to get DNA analysis back from a federal lab, WSDA’s molecular diagnostics lab is running its own tests and getting results back within hours. These quick results enable the program to make mid-season adjustments when responding to invasive pest threats, rather than having to wait until the following year. 

When responding to invasive pests – a quick response can mean the difference between eradicating an invasive threat quickly -- or having to learn how to manage it forever. 

The lab ran into a problem when starting to look into DNA analysis of snails: very little snail DNA exists in national DNA databases. Without enough samples to use for comparisons, the lab cannot provide meaningful DNA results. 

Sequencing snails

Snail segments from Germany
To beef up the snail DNA repository and help provide accurate snail DNA analysis in Washington and elsewhere, WSDA’s molecular lab is teaming up with USDA Animal and Plant Health Inspection Service (APHIS) National Malacologist and a Smithsonian research scientist to conduct a molecular study of Cernuella species from around the world. 

USDA APHIS is obtaining and expertly identifying the snails, WSDA is processing and sequencing the DNA, and the Smithsonian is analyzing the DNA sequences. 

This month the first (dead) snails arrived from Germany, and the WSDA molecular lab began the process of extracting and sequencing the DNA. When complete, the results will do more than just help WSDA quickly identify vineyard snail. It will provide agricultural authorities around the country needed DNA information to positively identify various Cernuella species and protect our nation’s natural resources from invasive pests. 

Electropherogram from German snail DNA
Helping protect the rest of the country from invasive species is not something new for WSDA. Washington’s location with its many ports as well as people moving into the region mean that the agency is constantly on the lookout for new pests – whether they be giant hornets, invasive moths, or even snails. Learn more about the Pest Program’s work on our website.