The prolific brown marmorated stink bug appears in dense populations, but what do we know of its economic threat to ornamental plants? According to research, it appears its stink may be worse than its bite.
Stink Bug images: Getty Images/iStockphoto
The brown marmorated stink bug (BMSB) is expanding its territory rapidly, and this invasive species has developed a palate for many species of plants. The pest has spread into more than 40 states, where it has been found feeding on a number of species not recorded in its native habitat in Asia.
Brown marmorated stink bugs have caused serious economic injury to many agricultural crops, but little is known about the economic threats to ornamental plants. BMSB adults have been observed feeding on flowers and seed pods of several ornamental herbaceous plants, but the damage to flowers, seed pods, stems and leaves has not been documented. Disease transmission from BMSB feedings on herbaceous plants has not been confirmed in the literature. Because of this dearth of knowledge, our team of researchers launched a study to determine if BMSB was a significant pest of herbaceous perennial plants growing in a commercial perennial plant production nursery.
What’s the damage?
Previous studies by University of Maryland researchers have determined that BMSB feeds and causes aesthetic damage to some woody ornamentals in nurseries and landscapes, where they tend to feed on the main trunk and branches. A 2011 field survey of trees and shrubs at a commercial nursery in Maryland showed 150 of 178 cultivars were used by BMSB (see sidebar). Certain host plants are used solely for feeding, whereas other hosts are used for feeding and egg-laying. Research in 2013 found that BMSB prefers London plane tree, flowering cherry, dogwood, catalpa and crabapple—while showing no preference for hawthorn, oak, elm or sweetgum.
BMSB also has been documented feeding on herbaceous transplants including snapdragon, petunia, dahlia and false indigo in a greenhouse setting. However, little is known about its effect upon herbaceous perennial plants in nurseries and greenhouses.
To help determine such damage potential, we selected three sites for our study: North Creek Nurseries in Pennsylvania; Holly Hill Farms on the eastern shore of Maryland; and Grasshopper Perennial Nursery in western Maryland. This latter site is in the epicenter of BMSB activity in Maryland, and had the strongest BMSB population pressure.
Site 1. Grasshopper Perennials
Grasshopper Perennial Nursery (GPN) is a small wholesale/retail operation near Sharpsburg, Maryland; the company both propagates and grows perennial liner plants for use in its landscape division, as well as for direct sale. GPN grows a wide selection of perennials (about 300 varieties), with approximately 50 percent of stock from seed/cuttings and 50 percent bought as liners and grown out for retail sale in quart to gallon pots. Plants are started and grown out in three unheated poly houses and overwintered in cold frames.
Grasshopper Perennial Nursery had a history of brown marmorated stinkbugs dating back to 2010. The owner reported high numbers of BMSB in the nursery yard, outbuildings and circa-1860 residence during the 2011 – 2012 season. Doorways and windows were covered with thousands of BMSB in fall 2012, and hundreds were found inside the house—”200 found per day” indoors in February/March. Overwintering BMSB were found by the hundreds between pots, bags of soil mix, between stacked pavers, and other places within the nursery grounds. The nursery has woodlands along the northern and southern borders, and agricultural fields on the western border (corn in 2012; soybeans in 2011).
BSMB performs a delicate balance on a Caryopteris bud.
Photo courtesy of Stanton Gill, D.S. Fiola
Reported ornamental hosts
Shade trees and woody ornamental plants: A wide variety, such as Abelia, Amelanchier (serviceberry), ash, birch, butterfly bush, catalpa, ornamental cherry, crabapple, dogwood, elm, euonymus, hawthorn, hibiscus, American holly, honey locust, honeysuckle, Japanese cedar, lilac, linden, magnolia, maple, mulberry, oak, Paulownia (empress tree), privet, pyracantha, redbud, rose, spiraea, stewartia, sumac, sweet gum, sycamore, tulip tree, viburnum, walnut, willow, zelkova; and weeds such as bittersweet, buckthorn and Russian olive.
Herbaceous plants: Perennials and annuals, including Celosia, Cleome, Dahlia, Nasturtium, sunflower; and weeds such as bur cucumber, burdock and nightshade.
At Grasshopper Perennial Nursery, perennial plants were monitored weekly in 2013 from the first week of May through mid-June, and then bi-weekly until frost (mid-October). Plants were located on 3-foot benches in the nursery sales area, and all plant material was grouped by cultivar. Plants adapted to shade were placed beneath shade cloth. All plants received daily irrigation—sometimes multiple times daily during summer months—and fertilized with controlled-release fertilizer. Pesticides were kept to a minimum as per previous organic certification.
Each cultivar of perennial plant was monitored for BMSB for a total of 5 minutes. Three to five individual plants were inspected visually for BMSB on foliage and stems, and then the pot was lifted to inspect for egg masses and life stages on the undersides of leaves. All sightings of BMSB were recorded for each plant, including life stage, time of day, weather conditions, feeding/nonfeeding, specific location on plant (leaf/stem/flowers/seed) and the percent damage.
A pyramidal tedder’s trap baited with USDA Pheromone #10 (changed monthly) and the commercial available pheromone lure (2E,4E,6Z=10:COOMe)—developed for another stink bug species called Plautia stali±and a Vapona kill strip was set up onsite to quantify the BMSB population pressure. Counts of all stages of BMSB were recorded at each monitoring visit.
Site 2. North Creek Nurseries, Pennsylvania
North Creek Nurseries supplies high-quality starter plugs to retail and wholesale nurseries, mail orders, garden centers and landscape professionals. This nursery specializes in perennials, ornamental grasses, ferns, vines and Eastern U.S. native plants.
The nursery is located on a state roadway and is separated from nearby homes on the northwest border by a narrow row of trees. The east border is a mixture of a wood lot or a narrow row of trees that provides a screen for homes. The west border has a large wood patch that extends around the southern border until it reaches a small field in the southeast.
In addition to nursery stock, the property also has an area planted with brambles and a number of vegetables. The growers at the nursery manage pests following IPM practices and generally do not allow their plants in production to produce flowers. Many of the propagated plants are on display in various flowerbeds throughout the property. These plants are maintained and permitted to grow naturally (for example, flowering, seed set and so on) throughout the year. Plants examined during the summer for this project were those in propagation houses closest to the western property border. A single pheromone trap identical to the one used at Grasshopper Perennial Nursery was used to monitor BMSB populations at the nursery.
Lifestyle of a prolific pest
The BMSB can be distinguished from other stink bugs by the distinct black with white banding of legs and antennae. Excellent pictures of additional life stages of nymphs and adults of BMSB can be found at www.stopbmsb.org.
As with other stink bugs, both nymph and adult BMSB use piercing-sucking mouthparts to feed on leaf and fruit tissue. This feeding, specifically the injection of digestive enzymes to facilitate nutrient extraction, results in localized necrotic spots. Damage is particularly problematic for direct feeding on developing fruit, which can lead to severe distortion and, in some cases, fruit drop.
Brown marmorated stink bug egg masses often appear on the underside of leaves, as seen on Persicaria. Here, a predatory chalcid wasp emerges from an egg case.
Photo courtesy of Stanton Gill, D.S. Fiola
BMSB has five nymphal stages, all of which feed on plant material. First instar (early- stage) nymphs do not venture very far from the newly hatched egg mass. Even though second through fifth instar nymphal stages do not have fully developed wings they are extremely mobile, moving several meters from egg deposition sites. We noted in our field studies that nymphs readily move from plant materials (1 to 3 meters away) to our baited pheromone traps.
Research in Maryland, Delaware and New Jersey has found that BMSB has two generations per year. Overwintering adults start laying eggs in June with egg masses being laid on foliage in clusters of 26 to 28 eggs, forming an overall wedge-shape. Eggs are usually laid on the underside of foliage. Hatching nymphs feed on a symbiotic (bacteria) on the eggs before dispersing on the foliage to feed on leaves, stems, fruit and seed pods. This symbiotic bacteria allows the insect to digest plant fluids. Nymphs are present from June through the early fall; adults and nymphs are present up to frost, but only adult males and females overwinter.
Three different stages of early instar BSMB nymphs can be seen on an egg mass: The dark red nymph (center) is a first stage or instar nymph; the lighter red one (top) has molted and is a new, second stage nymph; the black nymphs are second stage.
Photo courtesy of Gary Bernon, USDA APHIS, Bugwood.org
Research on the east coast has demonstrated that adult BMSB overwinter in structures such as houses, outbuildings and under the bark of standing, dead trees. Doo-Hyung Lee, a postdoctoral candidate working with the USDA to research BMSB, reported that overwintering adults prefer large, dry, dead-standing oak and locust trees, more than 60 cm in circumference, with porous dead tissue and peeling bark that gives BMSB a place into which to crawl. These structures and trees can serve as overwintering epicenters. And because BMSB prefers to feed on crops (such as soybeans and corn) during the growing season, structures adjacent to croplands endure significant late summer/ autumn migration and overwintering populations.
Hibiscus, Baptisia and Asclepias were grown in flats or pots depending on plant size, and were kept on greenhouse benches. Monarda, Phlox and Caryopteris were grown in flats or pots depending on size and were on the ground throughout the season. All production houses were covered with some shade-cloth, and the various cultivars of each species were usually grouped together. North Creek supplies a variety of other nurseries with plant material; thus some plants were not available to survey the entire year, and sometimes plants were moved from one house to another as their operations dictated.
Plants were visually inspected weekly from the first week of May until the second week of October. Time spent inspecting plants varied from one to five minutes, and depended upon plant structure, time of year and age of the plants. Plants were visually searched for adults or nymphs as described above at Grasshopper Perennial Nursery. We recorded the presence of BMSB adults, nymphs, egg masses, activity and location on the plant, plant phenology, other pests and natural enemies. North Creek pushes plant growth and tries to limit flower development on their plants; therefore, we rarely found flowers, flower buds or seeds on plants we were using in the study. Fifteen plants in individual pots or two to three flats of plants containing 15 to 30 cells were sampled from May until September. Ten plants in individual containers or two flats of plants were sampled from September to the end of the study because of time limitations.
Site 3. Holly Hill Nursery, Maryland
Holly Hill Nursery is a family-operated container nursery specializing in azaleas, rhododendrons, hollies, junipers, a wide variety of perennials, flowering shrubs and container-grown trees, among other plants. The company is located in the northern portion of the Chesapeake Bay region, about three miles from the mouth of the Elk River. The northern and western borders of the nursery are surrounded by riparian woodlots, whereas the eastern and southern borders are separated from cornfields by a narrow row of trees, many of which are black locusts. Hibiscus, Baptisia and Monarda were permitted to grow normally (flower, set seed). The greenhouses with the plants we studied were closest to the western property border. A single pheromone trap identical to the one used at Grasshopper Perennial Nursery was used to monitor BMSB populations at the nursery.
All plants were grown in pots on the ground throughout the season. All production houses were open (no shade cloth), and the various cultivars of each species were usually grouped together. Some plants were not available throughout the entire year (Caryopteris) because they were sold.
Plants were visually inspected weekly from the first week of May until the second week of October. Plants were sampled similarly to Grasshopper Perennial Nursery and North Creek. We sampled 15 plants of each species and variety from May until September, and 10 plants thereafter because of time limitations.
Trapping and counting
The baited pheromone traps confirmed that brown marmorated stinkbug pressure was consistent through the monitoring season, particularly late in the season as BMSB migrated from adjacent cropland to seek overwintering sites. The highest pheromone trap catches were in the greenhouse at Grasshopper Nursery: The pheromone trap captured a total of 3,745 BMSB from May through October. Adults were captured in the beginning of the season but in mid-summer immature forms dominated the trap catches.
BMSB found on perennials. BMSB found at GPN were feeding on 29 different perennial plants/cultivars. BMSB preferred to feed on flowers, buds or just under a bud —on the swollen peduncle/receptacle of a flower—and newly forming seeds or seedpods when existing on plants. The top two preferred perennial species at GPN—those both fed upon and visited by BMSB—were Althea lasiocarpus and Caryopteris ‘Dark Knight’, followed by Veronica ‘Sunny Border Blue’ and hollyhock ‘Halo Blossom’. Stokesia ‘Klaus Jelitto’ and Hibiscus moscheutos (dwarf rose mallow) also were visited by BMSB.
Peak activity of all BMSB life stages was from late August to early September (2586.0 to 2916.5 GDD[growing degree days]).
Brown marmorated stink bug
Photo courtesy of Susan Ellis; Bugwood.org
By late September/early October, adult BMSB at Grasshopper Perennial Nursery were migrating toward buildings, outbuildings and protected overwintering sites. Although few BMSB were found on plants in late October, a folded patio umbrella adjacent to the nursery yard, for example, was opened on October 4 to reveal hundreds of adults. The wild jimsonweed growing on the southwest side of the house had eight adult BMSB feeding on seedpods.
A few nonperennial plants grown at GPN had BMSB activity, including: marigold (annual), cleome (annual—BMSB found all over the seedpods late in the season), Buddleia (woody shrub), dwarf crepe myrtle (woody shrub) and Vitex agnus-castus (woody shrub).
In addition, in 2012 the grower stated that most of her personal sightings of adult BMSB were on garden phlox (Phlox ‘Franz Schubert’ and P. ‘Miss Lingard’), yet only two adults were spotted on these plants in 2013. The difference could hypothetically be that these plants had severe powdery mildew during the course of this study, and they were regularly sprayed.
Eggs. Only three egg masses were found on perennial plants at GPN in 2013, on Althea, Veronica and Persicaria. The cryptic nature of egg masses on the underside of foliage makes them very difficult to detect. Low-growing perennials, often with thick foliage, could not easily be held up to the light to detect shadows of potential egg masses. The first egg mass was found on July 12, 2013. No eggs masses were found on herbaceous perennials at Holly Hill Nursery or North Creek Nursery during the 2013 season.
There were very few sightings of BMSB on perennials in the shade at Grasshopper Perennial Nursery. It is not known whether the shade cloth covering this section of the nursery was a deterrent, or if BMSB simply preferred full sun conditions. The only shade perennials with adult BMSB noted and feeding were turtlehead, bleeding heart and foxglove (once, in late September). In a survey of greenhouse operations in Maryland in 2011 and 2012, we found that BMSB were rarely found in greenhouses during the growing season. We did find overwintering adults in greenhouses, but there was no evidence of feeding or egg-laying in commercial greenhouses. This may indicate BMSB preference for sunny spots and not filtered light areas.
We never saw BMSB on Monarda throughout the growing season. Likewise, no BMSB were found on Caryopteris, although we were able to observe fewer than 10 ‘Longwood Blue’ cultivars.
BMSB were quite active at GPN during the 2013 season, but did not cause aesthetic nor economic damage to perennials. No detectable necrotic spotting of foliage or stems was noted. No diseases were detected as being associated with feeding sites, and no feeding damage was found on any plants.
North Creek Nursery: Trap catches of BMSB in the pheromone trap at North Creek Nurseries were low (1,178) and not consistent until mid-August. Greater than 85 percent of the BMSB caught with the pheromone trap occurred from early September to the end of the project. The low numbers of BMSB in our sample observations and pheromone trap captures may result from a number of possibilities, such as low populations in the area; competition with more favored food sources elsewhere at the nursery (brambles, vegetables); presence of shade cloth; or phenology of the plants remaining constant throughout the growing season. Our observations of BMSB on plants were nymphs sitting/resting or walking on parts of the plant.
We did not see any visible sign of damage from the feeding BMSB adult on Baptisia. Brown marmorated stink bugs did not seem to be a problem for this nursery operation.
BMSB egg masses and feeding activity are noted on the following perennial plants as listed below:
Holly Hill Nursery: Catches of BMSB in the pheromone traps were much lower (462) than in Pennsylvania, and greater than 90 percent of those caught were recorded starting in early September until the end of the project. We did not see nymphs in the trap at this nursery the entire summer. The low populations at this nursery may be from low populations in the area or competition with more preferred food sources, such as nearby corn fields. Our observations of BMSB on surveyed host plants suggest much of their time is spent sitting/resting or walking on herbaceous foliage.
We did see feeding on Hibiscus near some exposed seeds toward the end of the project. Brown marmorated stink bug does not seem to be a management concern for this nursery.
What’s the verdict?
Brown marmorated stink bugs will visit and feed on a select number of herbaceous perennial plants, especially in high-population situations. Preferred feeding sites appear to be the flowers of perennials. The second most preferred feeding site is seed pods or fruiting parts of herbaceous plants. No detectable feeding or disease-transmitted injury was observed during the course of this project.
Despite the often alarming numbers of brown marmorated stink bugs found in and around structures and on other host plants, our study shows that BMSB does not appear to present an economic threat to perennial growers.
Stanton Gill is Extension Specialist in IPM for Greenhouses and Nurseries, University of Maryland Extension; he can be reached at firstname.lastname@example.org; Brian Kunkel is Extension Specialist in IPM, University of Delaware Extension; Karen Rane is Plant Pathologist and Director of the Plant Diagnostic Lab, University of Maryland Extension; Deborah Smith-Fiola is an IPM Consultant; and Suzanne Klick is Lead Technician, CMREC, University of Maryland Extension.