Title: Conservation Biology of Syrphids, Predators of Woolly Apple Aphid in Central Washington

Transcription

1 Title: Conservation Biology of Syrphids, Predators of Woolly Apple Aphid in Central Washington Principal Investigators/Cooperators: Elizabeth H. Beers, WSU Tree Fruit Research & Extension Center; William E. Snyder, WSU Dept. of Entomology (Pullman); Lessando Gontijo, Ph.D. candidate, Dept. of Entomology Key Words: conservation biology, insectary plants, cover crops, alyssum, nectar, pollen, syrphids, biological control, woolly apple aphid Abstract: Woolly apple aphid Eriosoma lanigerum is a secondary pest whose outbreaks have occurred more often since about The increase in aphid outbreaks appears to be associated with the changes in pesticide programs and disruption of biological control. Nevertheless, there is a good opportunity for biological control of this pest in orchards under soft pesticide programs. A preliminary survey of natural enemies conducted in 2008 has indicated that syrphids (Diptera: Syrphidae) are one of the most common predators found in woolly apple aphid colonies. One approach to enhance biological control is the conservation of natural enemies. This may be achieved by altering crop systems to provide necessary resources for beneficial insects. Adult syrphids are known to rely on the ingestion of nectar for energy and pollen for gametogenesis. Thus, engineering the orchard ecosystem to include flowering plants that provide these resources to adult syrphids should enhance biological control. The effect of sweet alyssum Lobularia maritima on the attraction of syrphids, and suppression of woolly apple aphid were examined in 2008 and 2010 respectively. Alyssum showed a high attraction to predatory syrphids. In addition, a faster aphid control was observed on alyssum plots compared to the check plots (grass). In 2011, we investigated the movement of natural enemies (especially syrphids) between alyssum and the canopy of the apple trees. Almost 50% of all syrphids, chrysopids and Aphelinus mali collected from the tree canopy tested positive for the marker, indicating movement of natural enemies between the cover crop and the tree canopy. This is further positive evidence to support the benefit of a flowering cover crop for enhancement of biological control in the apple system. Project Description: This experiment was conducted in late summer of 2011 in a 4-yearold unsprayed WSU research orchard (mix of the cultivars Gala, Ambrosia, Delicious, and Jonagold ). Because of its age, the orchard did not yet have a naturally occurring infestation of woolly apple aphid, thus the experimental design used sentinel trees (potted trees that were artificially infested) to measure natural enemy movement. Three sweet alyssum plots were tilled with a tractor-drawn rotovator a few weeks before sowing the seeds. To ensure high plant density and high germination rate, the seeds (American Meadows, Williston, VT) were sown by hand (ca. 150 g/plot). After sowing, the top 1-2 cm of soil was carefully turned over using a rake. The plots measured 15 x 3.6 m each, and spaced 40 m apart (east-west, across tree rows). Plots were irrigated 1 2 times a week via micro-sprinkler irrigation system (always after natural enemy collection). Four potted trees infested with woolly apple aphids (two on each side, near the tree rows) were placed on each sweet alyssum plot. The potted trees were heavily infested, and were replaced as necessary to ensure high aphid populations. The potted trees were Fuji September Wonder /EMLA 26 (C&O Nursery, 1

2 Wenatchee, WA). Because the field-planted trees were not infested with woolly apple aphid during the course of the experiment, the infested potted trees were the only nearby source of this aphid species. Egg protein (liquid egg white; All Whites, Crystal Farms, Minnetonka, MN) was used as an immnomarker to assess the movement of predators and parasitoids between sweet alyssum and apple trees. The sweet alyssum plots were sprayed with a 20% solution of egg whites diluted in water. Water softener (tetrasodium ethylenediaminetetraacetic [EDTA], The Herbarie at Stone Hill Farm Inc., Prosperity, SC) at a rate of 16 g per 10 liters of solution was also added to reduce water hardness. The egg white plus EDTA solution was applied once per week (28 June; 5, 12, 19, 27 July; 1, 9, 16, 23 August) using a 16-liter backpack sprayer (Smith Sprayers, Utica, NY). Immediately after each egg white application, white and yellow sticky traps were hung at a height of m on the canopies of infested potted trees and uninfested field-grown trees. Each alyssum plot had 1 yellow and 1 white sticky trap per tree on four field-grown trees and four potted trees per plot (two per side). In addition, two white sticky traps parallel to each other and 10 m apart were hung individually on the canopy of field-grown trees as described above at different distances away from the experimental area in the four cardinal directions (50 m on east, 100 and 200 m on west, 100 m on south, 100 and 200 m on north). At the same time the sticky traps were deployed, two cardboard bands were placed in each alyssum plot. One band was placed on an infested potted tree on one side of the plot, and one band on an unifested field tree on the other side. The natural enemy collection focused on beneficial insects that are known to feed on or parasitize woolly apple aphid. Natural enemies were collected 24 h after each spray and trap deployment. In addition to the sticky traps, natural enemies were also collected directly from tree canopies (2 infested and 2 uninfested trees from each plot) and sweet alyssum flowers by shaking their limbs and flowers respectively, onto a tray covered by waxed paper coated with adhesive (Tanglefoot ; Grand Rapids, MI). Samples of alyssum flowers and leaves were also collected at each time to confirm the presence of egg protein on the cover crop. Specimens caught on sticky traps and from tree canopy were processed before alyssum samples to reduce the risk of contamination with the marker. Natural enemies on the sticky traps and tray were removed with the aid of toothpicks (one per specimen to avoid contamination) and individually transferred to 1.5 ml microtubes. The microtubes were quickly placed into an ice chest for transport to the laboratory. Samples were stored at -4 C until they were tested for the presence of egg protein. After storage, the specimens were thawed and washed individually with 100 μl of 1X PBS (buffer) and then vortexed and centrifuged. The specimen was discarded, and the buffer wash was subjected to indirect enzyme-linked immunosorbent assay (ELISA, Jones et al. 2006) for detecting the egg protein marker. Work Completed: The three main predator groups of woolly apple aphid including syrphids, lacewings and coccinellids; and the parasitoid A. mali were found to visit the canopy of the trees after visiting the alyssum (Table 1). On the trees, 61.7% of predators were caught on white sticky traps, 29.5% on yellow sticky traps and 8.8% (earwigs only) were caught in cardboard bands. Syrphids were caught on sticky traps up to 200 m away from the experimental area (Table 1). These findings confirm that syrphids are attracted to alyssum, with a high probability that they use this plant as a food resource. The mobility of these predators also 2

3 suggests that alyssum could be planted in discontinuous strips in the orchard (e.g., every other row, every third row), which would likely reduce the cost of an insectary planting. In addition, the finding that A. mali and other aphid predators also visit the flowers increases the value of alyssum as an insectary plant. Spiders and earwigs were also found to move between sweet alyssum and trees. However, it is unknown whether these predators were attracted by the floral resource or merely picked up the mark in transit. Deraeocoris sp. was the only predator that did not test positive for the marker; however, it was caught in very low numbers (Table 1). Nabids and geocorids were the only predators that were caught only on alyssum plants; these predators either do not prefer an arboreal habitat, or are not attracted to woolly apple aphid. The results of this study confirm that syrphids and other natural enemies of woolly apple aphid move between the cover crop and canopy of the orchard trees. This suggests that that natural enemies that are attracted to the alyssum are staying in the orchard, or that the species attracted to aphid-infested trees are also visiting alyssum. Searching the tree canopy is essential for biological control of woolly apple aphid, which occurs on the tree branches from spring through fall. This study also showed that syrphids could fly considerable distances from a floral source, indicating that discontinuous patches of the floral resource might be sufficient to produce the desired effect. References Cited Ambrosino, M. D., J. M. Luna, P. C. Jepson, and S. D. Wratten Relative frequencies of visits to selected insectary plants by predatory hoverflies (Diptera: Syrphidae), other beneficial insects, and herbivores. Environ. Entomol. 35(2): Baggen, L. R., and G. M. Gurr The influence of food on Copidosoma koehleri (Hymenoptera: Encyrtidae), and the use of flowering plants as a habitat management tool to enhance biological control of potato moth, Phthorimaea operculella (Lepidoptera: Gelechiidae). Biol. Control 11, Berndt, L. A., S. D. Wratten, and S. L. Scarratt The influence of floral resource subsidies on parasitism rates of leafrollers (Lepidoptera: Tortricidae) in New Zealand vineyards. Biol. Control 37: Gurr, G., S. D. Wratten, and M. A. Alteri Ecological Engineering for Pest Management: Advances in Habitat Manipulation for Arthropods. CSIRO Publishing, Canberra. Haslett, J. R Adult feeding by holometabolous insects: pollen and nectar as complementary nutrient sources for Rhingia campestris (Diptera: Syrphidae). Oecologia. 81 (3): Horton, D. R., V. P. Jones, and T. R. Unruh Use of immunomarking method to assess movement by generalist predators between a cover crop and tree canopy in a pear orchard. American Entomol. 55 (1): Jones, V. P., J. R. Hagler, J. F. Brunner, C. C. Baker, and T.D. Wilburn An inexpensive immunomarking technique for studying movement patterns of naturally occurring insect populations. Environ. Entomol. 35(4): Kruess, A., and T. Tscharntke Habitat fragmentation, species loss, and biological control. Science 264:

4 Landis, D. A., S. D. Wratten, and G. M. Gurr Habitat management to conserve natural enemies of arthropod pests in agriculture. Annu. Rev. Entomol. 45: Lavandero, B. I., S. D. Wratten, J. Hagler and J. Tylianakis Marking and tracking techniques for insect predators and parasitoids in ecological engineering, pp In G. M. Gurr, S. D. Wratten and M. A. Altieri (Eds.), Ecological engineering for pest management: Advances in habitat manipulation for arthropods. CSIRO Publishing, Australia. Ponti, L., M. A. Altieri, and A. P. Gutierrez Effects of crop diversification levels and fertilization regimes on abundance of Brevicoryne brassicae (L.) and its parasitization by Diaeretiella rapae (M Intosh) in broccoli. Agric. For. Entomol. 9: Snyder, W. E., G. C. Chang and R. P. Prasad Conservation biological control: biodiversity influences the effectiveness of predators, pp In P. Barbosa and I. Castellanos (Eds.), Ecology of predator-prey interactions. Oxford. Tscharntke, T., A. M. Klein, A. Kruess, I. Steffan-Dewenter, and C. Thies Landscape perspectives on agricultural intensification and biodiversity ecosystem service management. Ecol. Lett. 8:

5 Table 1. Percentage of natural enemies from sweet alyssum, apple trees and distant traps that tested positive for the protein marker Natural enemies Sweet alyssum Infested trees Uninfested 50 m x 100 m x 200 m x Total N % positive N % positive N % positive N % positive N % positive N % positive N % positive Syrphidae Chrysopidae Chrysopidae larvae Coccinellidae Coccinellidae larvae Deraeocoris sp Nabis sp Anthocoridae Geocoridae Forficulidae Spiders Aphelinus mali Total x white sticky traps at different distances away from experimental area 5

6 Publications, Handouts: Gontijo, L. M., Beers, E. H., Snyder, W. E Effects of flowering plants on syrphid attraction and woolly apple aphid suppression. Western Orchard Pest and Disease Management Conference, January, 2011, Portland, OR. Gontijo, L. M., Beers, E. H., Snyder, W. E Biological Control of woolly apple aphid in Washington State. Washington State Horticultural Association Annual Meeting, 6-8 December, Yakima, WA [poster]. Gontijo, L., and E. H. Beers Stop and smell the flowers: An approach to attract syrphids into apple orchards, In Entomological Society of America Annual Meeting, December, 2009, Indianapolis, IN. Gontijo, L., E. H. Beers, and W. E. Snyder Conservation biology of syrphids, predators of woolly apple aphid in central Washington, 83rd Annual Western Orchard Pest & Disease Management Conference, [poster]. Beers, E. H Cover crops: Inviting Natural Enemies into Your Orchard 6th International IPM Symposium, March, 2009, Oregon Convention Center, Portland, OR. Gontijo, L. M., Beers, E. H., Snyder, W. E Conservation biology of syrphids, predator of woolly apple aphid in central Washington. BioAg Meeting, October 2008, Pullman, WA, [poster]. Outreach and Education Activities: Beers, E. H Disruption of biological control in organic orchards, 104th Annual Meeting of the Washington State Horticultural Association, 1-3 December 2008, Yakima Convention Center, Yakima, WA. Beers, E. H Controlling woolly apple aphid, Apple Day, 20 January 2009, Wenatchee Convention Center, Wenatchee, WA. Beers, E. H Woolly apple aphid control, NW Wholesale Grower Meeting, 28 January 2009, Wenatchee Convention Center, Wenatchee, WA. Beers, E. H Woolly Apple Aphid and Mites, Wilbur-Ellis Grower Meeting, 10 February 2009, Wenatchee Convention Center, Wenatchee, WA. Impacts: The May 1, 2009 Issue of the Good Fruit Grower had a picture of a syrphid on a zinnia taken on one of our experimental plants, with a corresponding article in the Organic and Sustainable Section. This article highlighted the syrphid conservation biology project, and the potential for using these plants to enhance woolly apple aphid biological control. As a result, one of the managers of the organic program at Dovex (which farms 2,200 acres of organic tree fruits in Washington), made test plantings of alyssum in their organic apple orchards. Fred Plath (Washington Fruit) planted the entire orchard floor of a new 20-acre block with an alyssum 6

7 ground cover based on the Good Fruit Grower article (see photos on last page). These events are indicators that producers are receptive to insectary plantings for difficult-to-manage pests. The use of cover crops like sweet alyssum is intended to enhance the biological control of orchard pests, and thus, reduce the use of pesticides. This allows for the establishment of a more stable and safer pest management that is also more environmentally friendly. Graduate Students Funded: This grant provided supplementary funding for Lessando Gontijo, Ph.D. student, Department of Entomology. Recommendations for future research. This project has shown that alyssum plants attract predatory syrphids into apple orchards, and that natural enemies are moving from the insectary plantings to the orchard canopy. The next step is to plant alyssum in commercial apple orchards that have a chronic infestation of woolly apple aphid, using various planting sizes (cover crop consisting entirely of alyssum, or alyssum planted in every third row), and compare this with a section where the cover crop remains in grass sod. Because of the potential for inter-plot movement, plot size will have to be quite large (2-5 acres), and replicated across, rather than within orchards. 7