After a long winter, the arrival of spring has many of us cheering. Ephemeral wildflowers, budding trees, and chirping birds are all welcome signs of nature breaking dormancy. For most people, the sights and sounds of the landscape coming back to life invokes a sense of happiness. The sight of the brown marmorated stink bug (BMSB) emerging from hibernation, on the other hand, is a springtime happening that is not well received. If you have not yet encountered BMSB in your area, chances are you will have the opportunity sometime soon, as this invasive pest is on the move. The good news is that: farmers, gardeners, and homeowners can create habitat for beneficial insects that attack BMSB.
BMSB Pest Status
Brown marmorated stink bug (BMSB, Halyomorpha halys) is native to Asia and was unintentionally introduced to the U.S. in the mid-1990’s. First detected in eastern Pennsylvania, the highly mobile BMSB rapidly spread to surrounding states. BMSB first made headlines when residents reported large numbers of the insect invading homes and other structures to seek shelter for the winter. BMSB quickly became more than an unwanted houseguest as the herbivore moved into orchards, farms, and gardens looking for host plants. Within a few years, BMSB gained recognition as an agricultural pest in most mid-Atlantic states causing significant damage to specialty crops including peach, apple, pepper, tomato, and sweet corn. BMSB is not a fussy eater, and since its arrival, this exotic species has been documented feeding on hundreds of plant species including ornamental landscape plants, wild woodland plants, herbaceous weeds, and agricultural crops. Research suggests BMSB prefer plants that develop fruits and pods, as the bugs are more abundant on plants that have these structures. A table of known host plants utilized by BMSB, including species that attract the highest densities, can be accessed online at www.stopbmsb.org (host plant information compiled by the Brown Marmorated Stink Bug IPM Working Group in conjunction with the Northeastern IPM Center). Now found in 42 states, the potential to become a serious pest in other regions of the U.S. is a growing concern, especially considering the very broad host plant range of BMSB.
BMSB Life Cycle
In late April to mid-May, adult BMSB emerge from their overwintering sites (e.g., underneath tree bark or inside houses), and can be found basking in the sun. A few weeks after emerging, female BMSB enter their reproductive stage and are ready to mate. Reproductive BMSB tend to disperse to nearby trees and shrubs after leaving overwintering sites, but before they invade crops, suggesting these woody plants may be important intermediate hosts. Female BMSB deposit an egg mass (clusters of about 28 eggs) on the underside of a leaf, and are capable of producing up to 10 egg masses during their lifetime. The eggs hatch into small black and red nymphs that go through five developmental stages (instars) before reaching adulthood. Adults begin to search for overwintering sites starting in September and continuing through the first half of October, and then the cycle repeats.
Managing Your Insect Allies
“The greatest single factor in preventing insects from overwhelming the rest of the world is the internecine warfare which they carry out among themselves,” said entomologist Robert Metcalf. If you are already battling damaging, invasive pest insects, the last thing that seems to make sense is inviting more insects to take up residence on your farm or in your garden. However, as Metcalf’s quote illustrates, nature has its own way of fighting back. In fact, among the huge diversity of insects with whom we share the planet, very few species are actually pests. Most insects are beneficial and provide important ecological services such as nutrient cycling, pollination, and biological control of insect pests of crops. Here we will focus on the key insect predators and parasitoids that attack BMSB and how to support them on the farm, in gardens, and around the yard by creating habitat composed of flowering plants.
Wasps are also often viewed as unwelcome guests due to the reputation of only a few species of yellow jackets and hornets, who are known to be aggressive and pack a painful sting. Unfortunately, these few species give other wasps, the kind you want to have around, a bad name. There are many species of solitary predatory wasps that may look intimidating, but are not defensive and do not have the nest-guarding instinct of yellow jackets and hornets. For example, predatory sand wasps are particularly promising as a natural predator of BMSB, as researchers have discovered this species provisioning its nest with the insects. Adult sand wasps vary in size (10 to 19 mm) and color; some resemble small cicada killer wasps with yellow- and black-striped bodies.
The larger yellow striped sand wasp Bicyrtes quadrifasciatus seems to have has shifted its host preferences from native stink bug species, and the majority of the prey found in its nests are now the invasive BMSB. The smaller and more common sand wasp, Astata bicolor, has also decided to include BMSB in its diet, but additional research on A. bicolor is required to understand the extent of the host shift. B. quadrifasciatus are found nesting where loose, sandy soil is plentiful, and many people report these wasps nesting in sand boxes, while A. bicolor prefers heavier soils and clears bare areas under vegetation for its nests. Attracted to stink bug odors, these wasps sting and paralyze nymphs to bury in underground tunnels. The tunnels are provisioned with up to a dozen BMSB nymphs on which developing wasp larvae feed until they pupate.
What to plant: In the adult stage, sand wasps feed on nectar and have a strong preference for flowers such as mountain mint (Pycnanthemum spp.), milkweed (Asclepias spp.), bee balm (Monarda fistulosa), and dotted mint (Monarda punctata), but will visit a variety other flowers in mid-summer as nectar is needed to complete reproduction. A diversity of other generalist insect predators such as lady beetles, lacewings, and assassin bugs will also prey on BMSB, and these beneficial insects benefit from the same flowering habitat as predatory wasps.
Most of the time flies are viewed as a nuisance, but again, many species are beneficial. Adult tachinid flies vary in size (5 to 20 mm) and resemble house flies, but they have stiff bristles on their abdomen that make them appear hairier. Coloration varies widely, although many are gray or brown with dark bristles, while others have vivid yellow or red markings or are metallic blue or green. Tachinid flies in the subfamily Phasiinae, are specialist parasitoids of stink bugs and squash bugs. Trichopoda pennipes, a brightly colored, orange-and-black tachinid is a major parasitoid of squash bugs and native stink bugs and has been discovered attacking BMSB. Most species of tachinid flies attack the immature life stage of their host, and the developing fly consumes the host as it grows.
What to plant: Adults tachinid flies are free-living and feed on floral nectar and pollen on which they must consume to reach reproductive maturity. Plants such as rattlesnake master (Eryngium yuccifolium), goldenrod (Solidago spp.), mustard (Alyssum), and milkweed (Asclepias spp.) are particularly attractive to these flies.
Parasitoid wasps, like predatory wasps, attack insect pests. However, parasitoid wasps are extremely tiny, much smaller than predatory wasps and parasitoid flies, and are easily overlooked. Females have an ovipositor, a stinger-like appendage used like a hypodermic needle to inject eggs into their hosts. Most parasitoid wasps are host-specific and are highly effective in regulating specific pests. The life cycle of parasitoid wasps is closely synchronized to that of their hosts. An adult female wasp finds a host at the appropriate life stage and deposits one or several eggs on, inside, or near the host. The larvae develop on or inside the host, feeding on it, and in the process, killing the host. Adult wasps emerge and seek new hosts to repeat the cycle. Several species are specialist parasitoids of stink bug eggs, and there is evidence that they are using exotic BMSB eggs as an alternate host. Many of these egg parasitoids are minute wasps in the superfamily Chalcidoidea. They are usually dark brown or black, but some come in various bright metallic green and blue colors.
What to plant: Adult parasitoid wasps are free-living and feed on nectar, extrafloral nectaries, honeydew, and occasionally pollen. Permanent plantings with a succession of flowering plants that bloom throughout the season, including species in the carrot, legume, aster, and mint families will support adult parasitic wasps and increase their longevity and reproduction.
What not to plant
In most cases, native wildflower habitats planted to attract beneficial insects do not serve as alternate hosts for crop pests or diseases. BMSM, however, can be an exception due to its broad host range and selected plants should be cross-referenced for their attractiveness to BMSB before planting. Plants that produce fruits or pods tend to attract more BMSB than plants without these parts. The plant species listed above, and many other flowering plants attractive to predators and parasitoids of BMSB, do not produce the large fruiting bodies attractive to BMSB. Highest densities of BMSB are often found on agricultural plants, but exotic ornamental plants and invasive weeds can also be hosts to BMSB. Avoid planting or remove plants such as tree of heaven (Ailanthus altissima), English holly (Ilex aquifolium), butterfly bush (Buddleja spp.), and other known host plants if BMSB is a concern on your property. Although BMSB are highly mobile, removal of host plants adjacent to farms and gardens may be effective in reducing BMSB numbers or discouraging colonization of nearby crops.
More information on how to protect and conserve beneficial insects can be found in The Xerces Society’s books Attracting Native Pollinators: Protecting North America’s Bees and Butterflies and Farming with Native Beneficial Insects: Ecological Pest Control Solutions or by visiting www.xerces.org.
This article was written by Kelly Gill, Mace Vaughan, and Thelma Heidel-Baker, and originally appeared in the Summer 2015 issue of Rodale Institute’s New Farm. New Farm is a quarterly publication given to members of Rodale Institute’s Organic Farmers Association. To become a member, visit rodaleinstitute.org/ofa.