Posted: August 12, 2013, 1:00 p.m. EDT
By John Dawes
The tobacco whitefly (Bemisia tabaci) is a widespread plant pest that causes serious losses in crops, including aquatic plants. While the whitefly can do considerable damage directly, the main cause for concern is the viruses it can transmit, which can lead to major crop losses.
Conscious of the growing threat posed by B. tabaci, the European Commission asked the European Food Safety Authority (EFSA) Panel on Plant Health to deliver a scientific opinion report on the risks to plant health within the European Union (EU), with particular reference to the viruses transmitted by the whitefly. This opinion was published in the EFSA Journal.
The document (www.efsa.europa.eu/en/efsajournal/doc/3162.pdf) identifies five entry pathways into Europe for B. tabaci:
- Plants for planting;
- Cut flowers and branches with foliage;
- Fruits and vegetables, including leafy herbs for consumption;
- Through human-associated means not involving plants, e.g., on vehicles or clothes; and
- By natural means, e.g., carried by wind or through active flight.
Entry of the insect via the ornamental aquatic sector falls within the first and most important of these pathways. Despite numerous interceptions of contaminated plants at ports of entry, the Panel on Plant Health concluded that "infection … shows that control measures and phytosanitary requirements in the area of production and inspection to prevent insects from entry have limitations.”
Amazon swordplants (Echinodorus spp) are among the many aquatic species susceptible to tobacco whitefly infection. Courtesy of John Dawes.
Referring specifically to aquatic plants, the panel stated that "Uncertainty … exists about aquatic plants entering the EU, on which B. tabaci is frequently intercepted … because it is unclear whether these plants are kept for further propagation or for direct marketing to the end user.”
The panel also referred to the European and Mediterranean Plant Protection Organisation, which reported that "the highest number of reports from interceptions (occur) on Euphorbiaceae and aquatic plants.”
While the insect has been found in a variety of plants, with the widest diversity originating from Israel, the panel said that "infested consignments from Singapore only comprised aquatic plants.”
Further, "Aquatic plants generated approximately 40 percent of all notifications for plants for planting.
These are traded in very high volumes and comprise more than 250 species originating mostly from Southeast Asia and Africa.” For the period 1998-2011, the number of interceptions of plants originating from Singapore was 331, accounting for 28 percent of all the interceptions made between 1993 and 2011.”
Although the whitefly spreads viruses, these pathogens "are not known to infect aquatic species, and it can be considered that aquatic plants do not represent a pathway for their introduction,” the panel stated. The list of aquatic plants on which B. tabaci has been detected at entry into the EU include some popular types, such as Hygrophila, Limnophila, Alternanthera, Echinodorus, Anubias, Bacopa, Hemigraphis, Cyrptocoryne and Ludwigia.
The Singapore Competent Authority—the Agri-food and Veterinary Authority (AVA)—is very proactive with regard to improving and safeguarding the reputation of its ornamental aquatic industry. Indeed, after the United Kingdom intercepted aquatic plants from Singapore in 2012 because they were infected with B. tabaci, the AVA rapidly imposed strict measures halting exports of seven types of aquatic plants to the EU. In the case of three genera: Alternanthera, Hemigraphis and Echinodorus, the ban spanned all species, affecting many more than just seven aquatic plants.
In view of its response to such matters, the AVA likely will welcome the news that a delegation from the EC’s Food and Veterinary Office will visit Singapore during the summer to discuss the tobacco whitefly issue. <HOME>
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