Key Words: conservation biology, insectary plants, cover crops, nectar, pollen, syrphids, biological control

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, nectar, pollen, syrphids, biological control Abstract: A group of six annual flowering plants were selected to determine their attractiveness to adult syrphids (Diptera: Syrphidae). This family of predatory flies had been identified as the most abundant predator in woolly apple aphid colonies in previous natural enemy surveys. The plants were selected on the basis of reports in the literature of attractiveness to syrphids and annual flowering habit. The plants were grown from seen in the greenhouse, and moved outdoors to a vacant field surrounded by orchards. Syrphids were observed at weekly intervals for 5 weeks, and adults collected for identification. All of the flowering annuals in the test attracted some syrphids; however, alyssum was significantly more attractive to adults than the other plants tested. Mustard and buckwheat were the next most attractive, with marigold intermediate, and zinnia and cosmos the least attractive. Alyssum, in addition to being highly attractive, possesses growth characteristics that will likely make it easy to manage in commercial orchards, including a long flowering period. Mustard, although moderately attractive to syrphids, was highly attractive to honeybees. This may be a negative management factor; in addition, it is possible that honeybees compete with syrphids for nectar resources on mustard. Project Description. This experiment was conducted in an open field that had formerly been planted to apple on the grounds of the Tree Fruit Research & Extension Center in Wenatchee, WA. The field was surrounded by apple orchards to the north and west, a cherry orchard to the south, and buildings to the east. A large tract of unmanaged ground with plants native to the shrub-steppe habitat adjoined the orchard area on the west. The treatments consisted of six different flowering plant species: marigold, Calendula officinalis; buckwheat, Fagopyrum esculentum; cosmos, Cosmos sulphureus; mustard, Brassica juncea;, zinnia, Zinnia hybrida; and sweet alyssum, Lobularia maritima (Plate 1a-f). All plants tested were annuals in the interior fruit-growing districts of central Washington. In addition to their flowering characteristics, the plants were chosen for their potential for easy management in the orchard floor, which requires multiple operations during the season (mowing, weeding, irrigation). The plants were grown from seed in a greenhouse in 10-in pulp pots, and then transported to the field after 10 d after germination (mid-august). The existing in-ground irrigation system (impact sprinklers on 2 ft risers) was used to provide moisture. Plants were irrigated as needed depending on ambient temperatures. The experiment was a completely randomized design, with six treatment and four replicates. Each replicate consisted of approximately 30 pots placed in a triple row (9-11 pots/row) in a 1.2 m rotovated strip in (Plate 2a) the center of the former drive rows of the

2 orchard 1. Plots were separated by empty spaces 35 ft in the east-west direction, and 50 ft in the north-south direction. Flower attractiveness was measured by recording the number of syrphid adults observed in 2-min observation period per replicate plot. After the 2-min observation period, adult syrphids were captured with an aerial net during an additional 1-2 minutes per plot (Plate 2b). These adults were collected for identification to species, and sent to the National Museum (data not available as of this writing). Evaluations were made on five dates at ca. weekly intervals during the month of September, Data were analyzed using the Statistical Analysis System (SAS 1988). Data were tested prior to analysis for homogeneity of variance using Levene s (1960) test. Variances found to be unequal were transformed [ln(y+0.5)] before analysis. PROC GLM was used to conduct an analysis of variance, and treatment means were separated using the Waller-Duncan k-ratio t-test. Work Completed: The number of syrphids observed in the 2-min observation periods was consistently higher in the alyssum plots (Table 1, Fig. 1, Plate 3). Mustard and buckwheat were also attractive, but less so than alyssum. Marigold was intermediate in attractiveness, while zinnia and cosmos attracted relatively few syrphids. The attractiveness of alyssum may have been due in part to its early and prolific flowering habit, but it also appeared to be intrinsically attractive. The average height for the various plants was buckwheat, in; sweet alyssum, 8.75 in; mustard, 32.5 in; marigold, 12.5 in; cosmos, 14.5 in; zinnia, in. Alyssum, in addition to its ability to attract adult syrphids, also appears to have favorable plant growth habits. It forms a low-growing mat of plants with a high flower density. Although the duration of this test was fairly short, it flowers very quickly from seed, with continuous flowering through frost. The early flowering habit of alyssum in this test may be partly responsible for the higher total numbers of syrphids observed. Mustard plants were considerably taller than alyssum, although with upright growth. One interesting characteristic of mustard was its potent attractiveness to honeybees (Table 1, Fig. 3). This attractiveness could have positive or negative effects, depending on the circumstances. If any pesticides toxic to honeybees were applied during the bloom period of mustard, bee kill could be substantial. In addition, the honeybees may compete with the syrphids for resources on mustard. Although we did not investigate this specifically, honeybees appeared to compete with syrphids for feeding sites; thus, syrphids may spend less time feeding on mustard, even though they were attracted to the flowers. Syrphid adults were captured roughly in proportion to their frequency on the various plants (Table 1). A total of 53 adults were captured, and have been pinned and mounted for identification to species. The species complex found in this study will be compared with the species complex found as larvae in woolly apple aphid colonies (Exps. 0618, 0718, 0801), to ensure that the species attracted will be useful for biological control. 1 A 1-meter strip in the drive row was rotovated with the idea that the pots would be buried for moisture conservation; however; for the sake of simplicity, they were placed on top of the soil.

3 References Cited Levene, H Robust tests for equality of variances. Chap. 25. In Olkin, I., S. G. Ghurye, W. Hoeffding, W. G. Madow and H. B. Mann (Eds.), Contributions to probability and statistics. Stanford University Press, Stanford, CA. Statistical Analysis Institute SAS/Stat User s Guide, Release 6.03 Edition. SAS Institute, Inc., Cary, NC. Table 1. Adult syrphids and honeybees observed or captured, TFREC, 2008 Syrphid adults/2 min observation Seasonal Treatment 1-Sep x 6-Sep 13-Sep 20-Sep x 27-Sep Sum Mustard 2.75 b 2.25 ab 2.25 b 2.00 b 3.25 b 50 b Buckwheat 4.00 ab 3.50 a 1.50 bc 0.25 c 1.50 c 43 bc Cosmos 0.00 d 0.00 b 0.25 c 0.50 c 1.00 c 7 d Zinnia 0.00 d 0.00 b 0.75 bc 0.00 c 0.50 c 5 d Alyssum 5.25 a 4.50 a 5.75 a 5.00 a 8.75 a 117 a Marigold 0.75 c 0.75 b 1.00 bc 0.75 c 3.50 b 27 c Honeybee adults/2-min observation Seasonal Treatment 1-Sep 6-Sep x 13-Sep x 20-Sep x 27-Sep x Sum Mustard 7.25 a a 6.50 a 4.75 a 5.50 a 149 a Buckwheat 5.75 a 0.75 b 0.25 b 0.00 b 0.25 b 28 b Cosmos 0.00 b 0.00 c 0.00 b 0.00 b 0.75 b 3 c Zinnia 0.00 b 0.00 c 0.00 b 0.00 b 0.25 b 1 c Alyssum 0.75 b 0.25 bc 0.25 b 0.00 b 0.00 b 5 c Marigold 0.25 b 0.00 c 0.00 b 0.00 b 0.50 b 3 c Syrphids captured/plot Seasonal Treatment 1-Sep 6-Sep 13-Sep 20-Sep 27-Sep Sum Mustard Buckwheat Cosmos Zinnia Alyssum Marigold Total captured: 53 Means within columns not followed by the same letter are significantly different, Waller-Duncan k-ratio t-test. x Data transformed due to unequal variances, y=log(y+0.5).

4 10 Syrphids adults observed/2 min Mustard Buckwheat Cosmos Zinnia Alyssum Marigold 0 30-Aug 4-Sep 9-Sep 14-Sep 19-Sep 24-Sep 29-Sep Fig. 1. Syrphid adults observed during a 2-min period on six flowering plant species, TF-19A, Marigold 27 Alyssum 117 Zinnia 5 Cosmos 7 Buckwheat 43 Mustard Syrphids adults/2 min (sum of 5 dates) Fig. 2. Sum of all syrphids observed during 2-min periods on six flowering plant species, TF- 19A, 2008.

5 Marigold 3 Alyssum 5 Zinnia 1 Cosmos 3 Buckwheat 28 Mustard Honeybees/2 min (sum of 5 dates) Fig. 3. Sum of all honeybees observed during 2-min periods on six flowering plant species, TF- 19A, Fig. 4. Correlation between syrphids observed and captured, TF19A, Zn, Zinnia; Co, Cosmos; Ma, Marigold; Bu, Buckwheat; Mu, Mustard; Al, Alyssum.

6 Plate 1a. Mustard. Plate 1b. Buckwheat Plate 1c. Cosmos. Plate 1d. Zinnia Plate 1e. Alyssum Plate 1f. Marigold. Plate 1. Flowering plant species constituting the treatments in the syrphid/flower attractiveness study, 2008.

7 Plate 2a. Rotovated strips in block TF-19A. Plate 2b. Lessando Gontijo capturing adult syrphids with an aerial net from potted flowering plants, TF-19A, 2008 (looking north).

8 Plate 3a. Syrphid adult on marigold. Plate 3b. Syrphid adult on zinnia. Plate 3c. Syrphid adult on mustard. Plate 3d. Syrphid adult hovering. Plate 3e. Syrphid adult on alyssum. Plate 3e. Honeybee on mustard.

9 Publications, Handouts: 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. 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 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. Additional funding applied for: I am a co-pi on a grant with Tom Unruh and Dave Horton to look at insectary plantings in orchards ($15,800, 1 year) to the Washington Tree Fruit Research Commission.. This grant will serve as part of the match for an OREI grant to be submitted early in I will be a co-pi on

10 this grant; many of the PIs are the same research and extension personnel that were awarded a $2.24 million SCRI project in Graduate Students Funded: This grant provided supplementary funding for Lessando Gontijo, Ph.D. student, Department of Entomology. Recommendations for future research. While this project provided the first step in implementing insectary plantings for woolly apple aphid, there are many practical issues which still need to be addressed. Will alyssum re-seed itself each year? Will it successfully compete with weeds? Will it tolerate mowing and traffic? In addition, we must demonstrate that biological control is indeed enhanced by this insectary planting, and preferably, that the need for pesticide applications is reduced or eliminated. In order to demonstrate this, we will need to test this system in large-scale replicated plots, preferably in an established commercial organic orchard with a history of chronic woolly apple aphid problems. We have been sampling the Plath orchard to get an idea of the seasonal phenology of syrphids and other natural enemies, however, there is no check, and the orchard is too young to have a woolly apple aphid infestation.

11 Mike Hargrove (manager), Betsy Beers, Fred Plath (owner) Fred Plath orchard with alyssum cover crop