ARS | Publication request: Parasitism of leafrollers in Washington fruit orchards is enhanced by perimeter plantings of rose and strawberry

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 25, 2012
Publication Date: N/A

Interpretive Summary: Leafrollers are the second most important insect pest of apples in central Washington and they account for up to 20% of insecticides sprayed on that commodity annually. They are also important pests of pears and cherries. These pests can be partially controlled by beneficial parasitic wasps in some years in some orchards, but growers cannot depend on the parasites and often revert to prophylactic pesticide use. A major probjem is that parasitic wasps cannot overwinter in apple orchards and if orchards are distant from overwintering sites of natural enemies, then biological control is compromised. Researchers at the USDA ARS Yakima Agricultural Research Laboratory and Washington State University Tree Fruit Research and Extension Center showed that planings of wild roses and strawberry near orchards are infested by a non-pest leafroller which is an overwintering host for an important parasite of apple leafrollers. This parasitic wasp leaves rose and strawberry gardens in spring to attack apple leafrollers in adjacent orchards in spring and summer and can dramatically increase leafroller control of apple leafrollers in orchards. Additional studies identified how to optimize rose and strawberry gardens for maximum productivity of the beneficial wasp.

Technical Abstract: Parasitism rates of leafrollers larvae attacking apple, pear, and cherry in Washington are typically low in spring. By providing an alternate, overwintering host for the parasitoid, Colpoclypeus florus, in perimeter plantings spring parasitism in orchards nearby was dramatically increased. Four gardens of multifloral rose, Rosa woodsii, and strawberry, Fragaria x ananassa, were planted adjacent to fruit orchards in the summer of 2000 and were infested with strawberry leafroller (SLR), Ancylis comptana, larvae which were naturally parasitized by C. florus in autumn. In spring 2001, C. florus left the gardens and parasitized sentinel Pandemis pyrusana larvae (PLR) in nearby orchards. In contrast, no parasitism by C. florus of PLR was observed near those sites in the previous two years. Parasitism rates on sentinal PLR in orchards within 600 m of two gardens were higher close to gardens. By walking on soy four dusted onto a rose garden C. florus acquired a mark later detected on individuals captured in traps in an adjacent orchard from 5 to 90 m away. The SLR in a rose and strawberry garden were mostly too small to be hosts for C. florus in spring, especially in roses, but mature, diapausing SLR were abundant in fall and were heavily parasitized by C. florus. Thus, C. florus uses SLR on which to overwinter but uses other leafrollers, such as pest leafrollers in orchards, during spring and summer. Strawberry is a better host for SLR than roses and acts as a partial refuge from parasitism by C. florus; parasitism of SLR in fall is higher in roses than in strawberry due to an orboreal search behavior by C. florus. These studies suggest rose and strawberry gardens may be a sustainable landscape modification to enhance biological control of leafrollers in tree fruits.