Feb 6, 2018Update on brown marmorated stink bugs
The first report of brown marmorated stink bug in the U.S. came from Pennsylvania in the late 1990s. It has been found in most of the continental U.S. with the exception of a few states. Since it was first detected in Michigan in 2010, brown marmorated stink bugs have continued to spread and grow in numbers. It is likely present in all counties in the Lower Peninsula. We have seen it progress from a household nuisance pest to an agricultural pest that is responsible for localized tree fruit injury, primarily in apples, each year. Michigan State University began conducting studies in 2011 to understand brown marmorated stink bug movement within the state and how this pest will affect the Michigan tree fruit industry.
This article provides a brief summary of some of the research produced by the institutions participating in a project titled “Management of Brown Marmorated Stink Bug in U.S. Specialty Crops” funded by the United States Department of Agriculture (USDA) and National Institute of Food and Agriculture (NIFA). It is not a detailed summary of all the work being conducted within this project, but provides highlights from areas of the project that may be of interest to Michigan growers.
Tracking movement by means of trapping
Researchers continue to track the movement and abundance of brown marmorated stink bugs. The largest populations and the most widespread damage to tree fruits is in the Mid-Atlantic region. In Michigan, we have seen brown marmorated stink bug numbers slowly build and currently the majority of the population is found in the southern third of the state with the highest numbers in the southern two tiers of counties. Damaging levels of brown marmorated stink bug do occur in localized areas north of this area and have produced fruit injury on individual farms north of Grand Rapids, Michigan, in the Ridge area.
The information required to detect the movement and relative numbers comes from trapping. A great deal of effort has gone into finding the most effective trap and lure. A variety of trap styles exist, but the pyramid trap baited with an attractant lure has been the standard way to detect brown marmorated stink bugs. Lures continue to be improved and the current standard is a two-part lure comprised of an aggregation pheromone and an attractant from a related stink bug.
A side-by-side comparison of the pyramid trap with an easier to use clear sticky trap on a 4-foot wooden stake using the same two lures has shown that the pyramid trap catches more stink bug adults than the clear sticky trap early in the season, and more adults and nymphs late in the season, but similar numbers mid-season. Importantly, the number of captured stink bugs on the clear sticky traps is positively correlated with the catch from the pyramid traps, which means the clear sticky traps could replace the pyramid traps and be used to determine presence, relative numbers and seasonal movement.
The pyramid trap was improved by replacing the dichlorvos strip killing agent with a piece of pyrethroid-impregnated netting. The pyrethroid in this case is deltamethrin. The netting is similar to mosquito netting used in malaria prevention programs and is commonly referred to as long-lasting insecticide netting. The benefits are that it lasts for the entire trapping season and is much safer to handle due to its low mammalian toxicity. Long-lasting insecticide netting also shows promise as a means of trapping brown marmorated stink bugs.
Using biological control agents
The most promising biological control agent continues to be a wasp parasitoid (parasites do not kill their host, but parasitoids do kill them) known as the samurai wasp, Trissolcus japonicas. This tiny wasp puts its own eggs into the stink bug’s eggs, and the developing wasp larvae use the stink bug egg for food until they emerge. In Asia, where brown marmorated stink bug originally came from, 60-90 percent of the eggs are parasitized by this wasp. Researchers in the U.S. have determined that the wasp highly prefers brown marmorated stink bug eggs over one of our native stink bugs eggs, spined soldier bug, so they should have little-to-no impact on them.
The USDA has yet to approve the general release of these wasps, but it is under review and could potentially happen at any time. Interestingly, like brown marmorated stink bugs, this wasp has been transported across the ocean. To date, populations have been detected in some Mid-Atlantic states and the Pacific Northwest and are slowly spreading on their own. However, if permission would be given by the USDA, they could be mass-reared and released where they would produce the greatest benefit.
Additionally, other brown marmorated stink bug predators and parasites, ones native to the U.S., have been identified and are being evaluated for their effectiveness. The particular insects attacking brown marmorated stink bugs vary according to habitat in each area. So far, the incidence of attack for these homegrown natural enemies of brown marmorated stink bugs is low.
Protecting natural enemies
Another area of interest is looking for ways to protect natural enemies from the negative effects of control procedures used against brown marmorated stink bugs. By carefully managing insecticide use, natural enemies may be preserved. One way to manage insecticide use is by establishing threshold levels for the pest. Determining an accurate threshold level requires testing over several years and in many orchard environments.
Research in West Virginia apple orchards has shown that a threshold of 10 brown marmorated stink bugs per trap can lower insecticide use by 40 percent compared to a grower standard program. A different trapping study compared brown marmorated stink bug captures in traps placed adjacent to wooded areas next to orchards to traps placed within orchards. The interior placement resulted in fewer nymphs captured, but adult catch was similar. However, there is still no clear relationship between the number of brown marmorated stink bugs captured in a trap and the amount of injury this level will cause in the orchard.
Insecticide assays in North Carolina showed that out of four Organic Materials Review Institute (OMRI)-approved materials (Entrust, Neemix, Pyganic, Azera), Entrust was the most harmful to two native parasitoid wasp species, even when exposed to 0.1X of the field rate. However, when exposed to residues of sugar-laced pesticides, only the lowest rate of Neemix had no impact.
In an Oregon study, more than half of the wasps exposed to dry residues of Actara, Asana or Admire Pro died within an hour of exposure. After 24 hours, mortality was greater than 75 percent for those materials and for Entrust and Exirel, but not for Altacor.
Using perimeter sprays and insecticide netting
A promising management tactic is attract-and-kill using pheromone-baited perimeter trees that receive either a regular insecticide application or have long-lasting insecticide netting within the canopy. Seven- and 14-day spray intervals using attract-and-kill or perimeter sprays were compared to 10 adults per trap (cumulative) threshold sprays of two alternate row middle applications and to a control. If the cumulative threshold level was met in the attract-and-kill or in the threshold spray plots, it also triggered two consecutive alternate row middle sprays.
Fruit injury was significantly reduced in the apple blocks using the perimeter sprays on seven- or 14-day intervals in the blocks using attract-and-kill with sprays at seven- and 14-day intervals or with long-lasting insecticide netting, and in blocks treated after reaching threshold levels of brown marmorated stink bugs, compared to the grower standard. This suggests perimeter sprays are an effective management tactic to employ against brown marmorated stink bugs.
Long-lasting insecticide netting placed in attract-and-kill trees in a vertical orientation killed more brown marmorated stink bugs than when the fabric was oriented horizontally. The level of injury to peaches and apples under grower standard programs was similar to the injury found when just orchard perimeters consisting of the exterior row plus one row toward the interior were sprayed. This did not hold for peaches if the orchard was 10 acres or more in size.
Another use of long-lasting insecticide netting is to drape a 5-foot by 5-foot section of it over a pole or fence and attach an attractant to the netting. Several of these are placed on the orchard perimeter between woods and the orchard. Brown marmorated stink bugs attracted to the lure come into contact with the pesticide in the netting and die. This may allow for interception of the adults before they enter the orchard resulting in less fruit damage.
Multi-state research efforts allow researchers to quickly acquire information that would take individual states or regions many years by themselves. Most of these experiments will be repeated in 2018 and new ones will be added as we continue to grow the knowledge base that allows us to successfully meet the challenges that brown marmorated stink bugs bring to the tree fruit industry.
Collaborators in this work include participants from 17 states including tree fruit personnel from MSU’s Department of Entomology. The other participants are North Carolina State University; Penn State University; Oregon State University; University of Maryland; University of Georgia; Washington State University; Cornell University; Utah State University; Rutgers University; The Ohio State University; University of Kentucky; University of California – Davis, Riverside and Berkeley; Virginia Tech; University of Minnesota; the North Central IPM Center and the Agricultural Research Service.
–Mike Haas and Larry Gut, Michigan State University, Department of Entomology