Aphids, long a dreaded pest in fruit orchards that cost millions of dollars to control, may in fact find new help from an odd quarter: flowers.
Washington State University researchers say that plantings of sweet alyssum, for example, attract spiders and other predator bugs that eat wooly apple aphids.
“The results are striking,” says Lessandro Gontijo, project leader of the WSU work. “After one week, aphid densities were significantly lower on trees adjacent to flowers than on control plots, and these differences were maintained for several weeks.”
To find the right flowers for the probe, scientists screened six possibles and, including marigolds and zinnias. They picked sweet alyssum since it attracted greater numbers of aphid enemies.
Researchers compared plots of apple trees with sweet alyssum to plots without the flowers. Although the flower attracted hoverflies the researchers found few hoverfly larvae, showing that the predators had only a marginal impact on the aphid population.
Researchers said a diverse population of spiders and predatory insects developed in the sweet alyssum plots. When the plants were sprayed with protein markers, many of the good bugs found at a distance from the flowers tested positive, showing that they had visited the blossoms.
“The wooly apple aphid is surprisingly damaging for an aphid, attacking tree shoots and roots,” says Betsy Beers, WSU entomologist. “These aphids also secrete a sticky liquid called ‘honeydew, which can coat apples, causing much annoyance during harvest.”
The aphids were previously kept at bay when orchardists sprayed pesticides to control codling moths. Since the phase-out of organophosphate insecticides, though, the wooly apple aphid has been making a comeback in central Washington and in other areas.
Sweet alyssum for biological control can be integrated with standard orchard management practices and should be particularly appealing to organic growers, who have fewer insecticide options.