Repelling pesticides, whitefly raids US crops

AFP

A tiny, invasive whitefly that is resistant to pesticides and carries crop-devastating viruses has been found outdoors in the United States for the first time, raising concerns among fruit and vegetable growers.
The Q-biotype whitefly turned up in April in the heavily manicured gardens of an affluent neighborhood in south Florida’s Palm Beach County, where landscapers were spraying the flowers and shrubs regularly with insecticides. Its discovery outdoors comes more than a decade after it was first found in a US retail nursery in Arizona.
Since 2005, the whitefly has also been found in about two dozen US states, but only in greenhouses. It is already considered a major invasive pest worldwide. Now that the Q-biotype whitefly is outdoors in the United States, researchers say it poses a serious threat to crops such as tomatoes, beans, squash, cotton and melons.
Having whiteflies outdoors makes the problem “much more difficult to control,” and they may never be fully eradicated, said Lance Osborne, a professor of entomology at the University of Florida. “The resistance to pesticides — that is what really sets them apart,” he told a few dozen growers who attended a recent session to learn about the whitefly in Homestead, an agricultural area south of Miami.
“The best single treatment we have kills 90-91 percent of them. That is as good as we can do without multiple applications.” Whiteflies draw fluid out of a plant’s leaves, and excrete a sticky residue that allows fungus
to grow, turning the leaves black
and making it harder for them to photosynthesize.
The insects can also spread more than 100 viral diseases that weaken the plants and can make fruits
and vegetables inedible. There are dozens of different kinds of whiteflies in the world. This one, known as Q-biotype whitefly (Bemisia tabaci), looks exactly like the silverleaf whitefly, or B-biotype, but is a completely different species.
The Q-biotype whitefly is believed to originate in the Mediterranean region, particularly from tomato fields in Spain, Portugal and Israel, Osborne said. Since its discovery outdoors in Florida in April, they have been found in more than 40 locations across the state, including residences, wholesale nurseries and retail plant outlets, crawling on the leaves of hibiscus, eggplant, lantana, ficus hedges and porter weeds.
Whiteflies can live on 600 different kinds of plants, 300 of which are grown in Florida, according to the state agriculture department. “The reason we are worried about the Q is because it has such a huge host range and is resistant to pesticides,” explained Osborne.
Whiteflies have been blamed for worsening famine in Africa and for wreaking havoc on farming in
the southern United States in the 1980s and 1990s. Back then, swarms of whiteflies of the B-biotype destroyed cotton, tomato and melon fields, causing hundreds of millions
of dollars in losses.
“The bottom line is, this can be
devastating,” said Osborne. To encourage growers to check their plants for whiteflies, the University of Florida has extended a pledge of
secrecy to anyone who wants to find out what kind of whiteflies they have on their plants.
Samples of whiteflies can be sent to their lab for DNA analysis, free of charge, and they promise the sender won’t be identified except by county and the general type of location.