The winter moth caterpillars are tiny when they attack tree buds. When they emerge they are about 1/2 inch long, and then drop to the soil to pupate and emerge in November/December as moths.
The bands on these trees in Goddard State Park were used last fall to trap winter moths in order to get a population count sufficient to launch the biological control project this spring.
Lacey, holey, deformed leaves are the result of winter moth caterpillars munching on tree buds in early spring. For fruit growers, the damage means a harvest reduction.
The parasitoid flies are smaller than houseflies and much more docile--they can be scooped up easily with a plastic cup.
The biological control flies snack on sugars and moisture on an apple before being released.
By RUDI HEMPE,
CELS News Editor
Winter is finally over and for some fruit growers a pest that has become a part of the frigid season is giving them economic headaches.
The so-called “winter moth” has invaded parts of Rhode Island and has caused fruit loss in some apple orchards and blueberry fields, not to mention damage to other trees and shrubs, but URI researchers in concert with UMass have launched a counter-attack.
On Friday, April 22, researchers Heather Faubert, head of the URI Plant Protection Clinic and Joseph Elkinton, a UMass, Amherst entomologist, released 750 parasitoid flies in Goddard State Park in the first step to try to curb the population of winter moths which in caterpillar form munch on fruit buds reducing fruit harvests.
The release is the first time a biological control has been attempted to control the winter moth in the state although similar releases have been done in Massachusetts and originally in Nova Scotia.
The winter moth (Operophtera brumata) was first discovered in Nova Scotia in the 1930s, an invader from Europe. Since the females cannot fly, the spread of this pest was slow but in the 1990s the moth was found on Cape Cod. In 2004 it was reported in Rhode Island in the Bristol/Barrington area and one year later in Warwick. Parts of northern Rhode Island where apple orchards abound, had problems with the pest.
The moth in its caterpillar stage attacks a host of deciduous trees and shrubs. The caterpillars feed on the leaf buds of tree. When the buds open up, the leaves appear “lacey” or shot full of tiny holes. On fruit trees and shrubs, the caterpillars feed on fruit buds resulting in a loss of fruit production.
Using a general insecticide, fruit growers can spray but the timing is critical—once the tiny caterpillars (they are about ½ inch long at maturity) get into a fruit or leaf bud, they are shielded from pesticides.
After the caterpillars gorge themselves on buds, they drop to the ground to pupate under the soil. They emerge as moths in November/December, hence their common name. The males, attracted to light, can often be seen swarming around streetlights that time of year.
The females lay their eggs in the tree bark crevices and on branches. Sprays are effective before the eggs hatch in early spring.
Spraying, of course, can be expensive and complicated for conventional growers and problematical for organic growers. Hence researchers in Nova Scotia started looking for a biological control. They found one—a fly, smaller than a housefly and quite docile, called Cyzenis albican, also from Europe.
Testing biological controls is time-consuming. Just obtaining the permits to bring in a new critter means getting by many bureaucratic hurdles. Evaluating the results can take years.
The parasitoid fly in this case also lays its on the buds and leaves of trees. When the winter moth caterpillars start feeding in the spring they ingest the eggs of the fly. The eggs hatch into maggots inside the winter moth caterpillars and start feeding, wiping them out in the process.
Faubert said she and others will sample the results in May but explains that it may take five or six years to see any noticeable changes in the winter moth population. The first fly release was done in Massachusetts in 2005 and the successful results were not observed until last year.
“It’s kind of like winning the lottery,” she said
Faubert has been involved in other biological control projects at URI over the years. As head of the Plant Protection Clinic she advises growers all over the state on crop problems and also analyzes plant problems in her lab for landscapers and homeowners.
The anti-winter moth campaign has been years in the making, she said. For a true test of the biological control, it had to be established that the winter moth population was high enough. Last fall, she and her daughter applied sticky bands to trees in Goddard State Park. The bands trapped the moths as they were in the process of laying eggs and so a moth count was possible.
Goddard Park was chosen for two reasons—it was on the mainland near winter moth infestations and it was on public land where no pesticides were applied.
Monitoring the success of the biological control of winter moths will probably take years but for those growers who prefer not to have the hassle and expense of spraying, it might be well worth the wait.
Published: May 1st, 2011