Rose habitats to enhance leafroller biological control in pome fruits

Rose habitats to enhance leafroller biological control in pome fruits

Summary

Easily sustainable rose/strawberry gardens near orchards provide an alternate host (Ancylis comptana) for a parasitoid (Colpoclypeus florus) of pest leafrollers. Fall parasitism approached 100% in roses and 50% in strawberries showing both plants are useful. Parasitism at 11 orchards was mostly C. florus in the spring and early summer. April parasitism was mostly near the gardens around a 100-acre orchard. A study where a garden was marked showed marked C. florus individuals captured up to 125m into the adjacent orchard. Presentations were made to grower groups (4), a grower-targeted paper was published and web page on gardens was created.

Objectives/Performance Targets

• 1. Evaluate the impact of large gardens of Rosa woodsii and wild strawberry harboring the strawberry leafroller, Ancylis comptana (SLR), which supports C. florus overwintering and enhances parasitism of OBLR and PLR in adjacent orchards.
  2. Disseminate information on how to establish, maintain and benefit from these alternate habitats through traditional presentations, grower magazines, a web site and consultation.
  3. Develop greater understanding of the ecology of this system, particularly how far into orchards parasitoids disperse from gardens and the stability of the beneficial community in gardens with rose alone versus strawberry alone and rose plus strawberry.

Accomplishments/Milestones

ACCOMPLISHMENTS

Highlights
1. Demonstrated spatial patterns of parasitism by C. florus in spring were associated with the nearby gardens on the orchard perimeter.
2. Demonstrated that 82% of gardens harbor the beneficial alternative host leafroller Ancylis comptana and 90% of these showed parasitism by C. florus.
3. Showed that parasitism of Ancylis in gardens by C. florus was related to the height of the Ancylis with parasitism much high on the higher rose foliage and experimentally elevated strawberry foliage compared to strawberry foliage on the ground and Ancylis in leaf rolls of low-hanging branches of rose. This pattern resulted in nearly 100% parasitism of Ancylis in roses while only 50% were parasitized in strawberries, supporting the idea that
strawberries help maintain this 2 species trophic system in the gardens.
4. A website was created to describe planting, placement and maintenance of gardens with links to articles, essays and websites on why do this habitat manipulation and the biology of the pests and beneficial insects.
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Materials and Methods

Parasitism is assessed by deployment of sentinel 4th instar OBLR directly onto the leaves of apple or cherry trees and exposure of these to parasitism for 2 weeks. Larvae are then collected and reared to adults using clean apple leaves as food as needed. Parasitism is calculated from the proportion of parasitized hosts where parasitoids emerged divided by the total number of moths emerged plus parasitized hosts. To initially infest gardens, leafroller-infested foliage is placed onto growing strawberry and rose foliage in the early fall following planting and again during the following summer. In most cases this approach has led to establishment of this leafroller. In some instances the infestation procedure was repeated during a second summer.

Results and Discussion

Accomplishments under objective 1

Success in enhancing biological control of leafrollers through habitat manipulation first requires the presence of a stable population of the alternative/overwintering host, Ancylis comptana. Ultimately 75% of gardens were successfully infested with Ancylis (Table 1) and there was a trend that the chances of success increased when a healthy understory planting of strawberries persisted (strawberries are the preferred host of Ancylis comptana). Ninety percent of gardens with Ancylis showed parasitism by C. florus in adjacent orchard.

Seasonal parasitism studies in 2006 focused on patterns of parasitism early in the season when parasites are just entering orchards from adjacent garden overwintering sites. This contrasts with the work in the preceding 4 years when parasitism through the season in orchards was monitored. In early spring of 2006 sentinel leafrollers were deployed around the periphery and internally in a 100 acre IPM orchard that has 4 gardens planted also on its periphery. Parasitism around the perimeter was associated with garden sites (red dots) and surprisingly all interior sites show early spring parasitism (Figure 1 not available online). The presence of C. florus attacking sentinel larvae in the interior early in spring suggests at least 3 nonexclusive hypotheses that merit research in 2007. H1) larger than expected pest leafroller larvae are present in the orchard in fall and are attacked by C. florus late enough in the season that they overwinter. This may arise from some segment of the normal overwintering generation of OBLR larvae attaining 4th instar in the fall (or larger), or the presence of laggard larvae from the first generation. These effects may be induced by insecticides that delay insect development. H2) There is an alternative host other than OBLR, or Pandemis in the orchard interior. H3) C. florus readily flies deeper into the orchard, but not around its periphery, to search for hosts.

Our traditional season-long studies of parasitism were restricted to 11 orchards in 2006, and in general we found lower than normal parasitism rates. However, the seasonal pattern observed from sentinel deployments of OBLR in orchards demonstrated a large excess of spring to mid-summer parasitism due to C. florus while later in the season parasitism by tachinid flies became more abundant at some sites. (Figure 2 not available online).

Accomplishments under Objective 2.

To date we have presented our results of the first year of this WSARE project at the third National Organic Tree Fruit Symposium held in Chelan WA in June 2005 and at the Washington Horticultural Association Convention held in Wenatchee in December 2005 and 2006. We also provided written, oral and poster reports to the Washington Tree Fruit Research Commission in February 2006 and an oral presentation to the 79th annual Western Orchard Pest Management and Disease Workshop in Portland Oregon in January 2006.

Milestone: We have created a website (http://www.ars.usda.gov/Research/docs.htm?docid=14646) describing how to implement gardens including how and where to plant and maintain the roses and strawberries, where to find infested roses for transferring Ancylis to a new garden, and overviews of our results for the last 5 seasons. The website also provides links on insect biology and to articles and reports related to this work. While we will continue to provide information to growers on how to create gardens through direct contacts, the new website represents a decentralized approach for growers to get this information.

Accomplishments under objective 3.

A greater understanding of the ecology of Ancylis and the various parasitoids in the rose gardens was our highest priority area of study in 2006. We specifically addressed the importance of strawberries in the mixed planting gardens. Colpoclypeus florus parasitizes more strawberry leafroller (SLR) hosts in roses than in strawberries. This is related to plant height; when strawberries with 25 SLR were exposed to parasitism on wire shelves parasitism increased with height exposed (Fig. 3a, below left, not available online). Also, parasitism pf SLR increases tremendously in late summer into fall with parasitism of roses approaching 100% while that on strawberries ending up just over 50%. This demonstrates that strawberries can complement roses by providing a refuge from parasitism for the SLR. This refuge prevents the wasp from completely decimating the host leafroller in fall-winter (Fig. 3b below right, not available online).

Impacts and Contributions/Outcomes

This report covers 2.5 years of a three-year project. We have no impacts measured as pesticide reductions to report and posit that 3 years is too short of a time to measure the impact of such fundamental and broad-scale habitat manipulations on pesticide use practices. However, significant milestones are being met specifically through grower education with the larger grower community of the Pacific Northwest on the potential of rose garden habitats to enhance biological control of leafrollers. Potential impacts include dramatically reduced pesticide use for leafroller control in apple pear and cherry and a more biocontrol-oriented selection and timing of control methods used for the codling moth and aphids in the crops. A hit counter on the website will represent a tangible method to discover the reach of the website.

Collaborators: