ABERDEEN PROVING GROUND, Md. (May 8, 2015) -- Invasive insect species pose a considerable threat to U.S. agriculture and natural resources - making it imperative that known invasive species are detected and their introduction prevented throughout global trade pathways.
Smaller than a grain of rice (three millimeters or less than an eighth inch long), the khapra beetle is difficult to control and can survive nearly anywhere they are protected from cold temperatures. Preferring low-moisture foods, khapra beetle larvae can destroy a significant proportion of unprotected grains stores due to their "dirty eating" behavior - a feeding habit, where the beetle eats only a little of a single grain before moving on to others.
In addition, khapra beetle contamination in food products presents a food safety concern as the hairs associated with larvae and cast skins are potential allergens and respiratory hazards, particularly for young children. Notorious as the only stored product pest with quarantine status in the United States, the khapra beetle is also the only pest, which automatically triggers rejection of import shipments based solely on discovery of non-living life stages, cast skins or other body parts of the insect.
Underscoring this severity was an incident in 1953, where khapra beetles were discovered in California, resulting in a 13-year, $15 million eradication effort. Adjusted for inflation, that cost would be equivalent to $131 million today.
Current inspection methods involve targeting imports from countries, where khapra beetles are known to be present, and visually examining high-risk commodities.
Department of Homeland Security, or DHS, Customs and Border Protection Agriculture specialists are required to open shipping containers to look for evidence of khapra infestation - a task that is extremely difficult considering the size of the insect, and puts surrounding shipping containers at risk for contamination. Detection of khapra beetle is particularly challenging as the beetle is capable of living for years without food and can be found in non-food commodities such as textiles or packaging materials.
To address the khapra issue, scientists at the Edgewood Chemical Biological Center, or ECBC, are helping the DHS Science and Technology Directorate, or S&T, and the U.S. Department of Agriculture, or USDA, Animal Plant Health Inspection Services, or APHIS, Plant Protection Quarantine, or PPQ, find an easier, more effective way to inspect bulk food supply for khapra beetles.
In a project funded by the DHS S&T Seedling Program, under Interagency Agreement, HSHQPM-14-X-00086 and leveraging support from the Defense Threat Reduction Agency, ECBC researchers in partnership with iSense LLC, are studying the use of colorimetric sensor arrays, or CSAs, to detect this invasive species in shipping containers.
These inexpensive, disposable sensors, manufactured by iSense, are approximately one square inch in size (about the size of a postage stamp) and spotted with 73 dyes, which change color in response to various vapors which come in contact with the CSAs from the sample. Samples are identified, not by any single spot color change, but instead by the combination of color changes across multiple spots forming a "fingerprint" that can be used to identify compounds found in a sample.
The CSA color changes are sensitive enough to detect even trace amounts of some vapors (odors), allowing for the broad spectrum detection of a number of volatile organic compounds, or VOCs, which may be well below concentration levels attributable to health risks. A wide range of patterns or signatures, resulting from emitted VOCs, can be elucidated and stored for various compounds, creating a reference library for any previously recognized material.
During an assay, CSA sensors are exposed to odors emitted into the headspace above bulk grain infested with beetles. Over time, changes in the colored spot patterns emerge, and by using special software designed specifically for this project by Charles Davidson, Ph.D., unique color fingerprints are revealed.
The goal of the project is the development of unique and individual spot patterns capable of differentiating between invasive, quarantined khapra beetle infestation and other non-invasive species.
Detection of infestation is based on volatile signatures within a closed container - a method, which has the potential of allowing infested cargo to be sequestered before being opened, thereby mitigating exposure or release of the species within. With success, this technology could transition into a self-contained sampling and detection unit, which could wirelessly transmit results to a smart phone for analysis.
"Our vision is to create remote interrogation of shipping containers that reduces the burden on the customs officials," said Jeff Ballin, Ph.D, ECBC lead for this project.
ECBC envisions a solution, where an inexpensive, disposable reader could be placed within a crate before shipment, then later queried by a smart phone to allow inspectors at the port of destination to assess food security and quality without ever having to open the container.
The first step in making this method a reality is the development of a reproducible signature library capable of differentiating between beetle-infested grain and pristine grain.
Since khapra beetles are a quarantined species, scientists began testing the CSAs using the common warehouse beetle, which is closely related to the khapra beetle. The team simulated the highly-infested environment of shipping containers by using grain-filled glass mason jars either with or without beetle contamination. The CSAs were placed in the jars and scanned at regular intervals to track color changes.
"In most projects we do, we have a physical model of how the project should behave (e.g., how a beetle eats and breathes)," said Avishai Ben-David, Ph.D., a researcher with ECBC. "In this case, we have no model or precedent to how a single beetle behaves; we are creating all of these models right now [from observations] much like the Human Genome Project."
While the research is still in its infancy, researchers have been able to distinguish between the warehouse beetle-infested and non-infested grain based on the response of the CSAs to the VOCs present in the headspace above the grain. The information that has been gathered is foundational in moving the project closer to its goal of creating an inexpensive, disposable tool to query shipping containers, which will allow inspectors to assess food safety without ever opening the container. The group expects to complete its first round of testing by the fall of 2015.
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The Edgewood Chemical Biological Center is part of the U.S. Army Research, Development and Engineering Command, which has the mission to empower the Army and joint warfighter with technology and engineering solutions that ensure decisive capabilities for unified land operations. RDECOM is a major subordinate command of the U.S. Army Materiel Command.
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