The brown marmorated stink bug (BMSB), Halyomorpha halys (Stål) (Heteroptera-Pentatomidae), has established itself in our surroundings and most likely will continue to pose an extremely serious threat to our agricultural systems for years to come. During the last few years researchers and extension specialists throughout the Mid-Atlantic States have documented the enormous potential of this insect to destroy the quality of various fruits, vegetables, and some agronomic crops, such as soybean and corn. According to information gathered by the U.S. Apple Association, the estimated losses during the 2010 season for this region's fruit growers exceeded $37 million.
Damage on fruit caused by BMSB feeding can occur throughout the entire growing season. Although the mechanism by which BMSB feed on fruit is similar throughout the season, the time of the season the feeding occurs can have a profound influence on the type and appearance of the injury. For example, early season feeding usually causes misshapen fruit, whereas, late season feeding usually causes depressions on the fruit surface and the appearance of necrotic tissue (corking) just below the fruit surface. Late season feeding injury is often confused with the physiological disorder called "corking," which is caused by a calcium deficiency. Although the amount of damage varied significantly among various locations throughout the state in 2010, some stone or pome fruit orchards suffered more than 60 percent injured fruit by harvest.
The management options for BMSB populations are quite complicated and, as observed during the last few seasons by some growers dealing with this challenging pest, also quite frustrating. Despite using the best available practices to conserve our IPM program and utilizing the most effective insecticide products and tactics, fruit injury levels in affected orchards can range from low to extremely high, with most being well above acceptable levels to growers and costumers.
Following are some of the possible reasons for the observed problems in the management of BMSB:
Unique elements of BMSB biology
Although more and more observations suggest that BMSB adults can survive the winter without the protection of human-made structures, at this time we still believe most BMSB adults overwinter inside some kind of dwelling located mostly outside of orchards or other agricultural settings. In the spring, adult BMSB adults leave their overwintering shelters, looking for any green plants to serve as possible food sources. The spring emergence of adult bugs from overwintering sites is usually very extended, lasting from late April until early June. These differences in the starting point for overwintering adults likely create a situation that allows all possible BMSB nymphal and adult stages to be present in the orchard at the same time. Throughout the season, BMSB adults at any point can start moving into orchards or between orchards. Feeding on stone fruits seems to be the preferred early season behavior, but these hosts are not exclusive food sources and any green, growing plants (including pome fruits) can also be utilized. Reports in the scientific literature estimate that BMSB can feed on 250 to 300 different host plants. Later in the season (i.e., late June, July, August, and September) various instars of BMSB are frequently observed feeding on apple, pear, and small fruits, including various berries and strawberries.
The BMSB host plant choice is still not well understood. We still do not know exactly when and, more important, why BMSB moves from one host to another. It is important to understand that BMSB can move to orchards at any time from May until October, including possible multiple, consecutive influxes from surrounding vegetation. Effective control of one wave of stink bugs in the orchard does not prevent another wave of BMSB from entering the orchard a short time later. And since BMSB is not a resident pest in the orchard, even the best management activities against the pest in the spring will not prevent new stink bugs from invading again later in the season, even in October. Therefore, it is quite obvious that in addition to using effective insecticides, the most crucial, practical element for successful BMSB management is the development of a reliable pest detection and monitoring strategy.
Efficacy of insecticides
Our laboratory bioassays evaluating the effectiveness of various insecticides against adult stink bugs demonstrated the availability of multiple active ingredients that are effective against brown marmorated stink bug. These bioassays also identified a large group of currently registered products, which provided very minimal direct mortality of BMSB adults. Although evaluations of available insecticides were conducted using different bioassay methods, the results provide a good complementary picture of what to expect from various products. The "lethality index" developed by USDA researchers provides information on efficacy of products against adult BMSB after exposing them for 6 hours to a dry residue of insecticides, while the Penn State "percent mortality" readings provide information on the mortality of adult stink bugs after direct contact with 2 µl of an insecticide solution applied directly to the dorsal part of the insect abdomen. Both methods utilized long-term observations (up to 120 hours after treatment) to develop the final results.
Suggestions for BMSB management in Pennsylvania fruit orchards
The laboratory bioassays demonstrated various efficacies of currently registered insecticides against BMSB adults. With 10 various active ingredients (from four different Insecticide Resistance Action Committee [IRAC Groups]) causing above 50 percent mortality during the direct contact bioassays, it appears there are enough products to control BMSB populations entering orchards throughout the entire growing season. However, a big challenge with this seasonal approach is to manage the usage of these various products so they provide not only the best control against all stages of stink bug but also all other pests present in the orchard throughout the season. Available products are not equal in their efficacy against stink bugs and they are also not equal in their activity against other pests at the time when insecticide applications might be needed. A grower can choose to ignore these other pests and concentrate only on the management of BMSB, but based on our experience from the era "before the stink bug," it might not be the best option especially with known pressures in our orchards from such pests as codling moth, Oriental fruit moth, and leafrollers.
When developing a seasonal strategy to manage BMSB at any particular location, the following factors need to be considered during the planning process:
Chemical efficacy and other considerations
The efficacy ratings for either direct contact or residual toxicity against BMSB are two of the most important factors in choosing the best product(s), but growers should also consider the time of the season and what other pests are likely to be active in the orchard. Also, factors such as an insecticide's preharvest interval (PHI), the number of allowed applications per season, and the amount of an insecticide active ingredient that can be used for the entire season (be aware of multiple products with the same active ingredients) need to be critically assessed. While it may be wise on stone fruit to use the more effective products earlier in the season, the same products on apples may be much more valuable for BMSB control in August, September, or October. Since all products have a limited number of applications and active ingredients that can be used during a season, utilizing the most effective insecticides before they are essentially needed will likely leave us with only less effective alternatives later in the season.
Expected sources of BMSB influx
Population pressure from BMSB is not uniform from outside or within any particular orchard, but it also fluctuates during various times of the season. Some orchard blocks located next to woods may not have to deal with stink bugs until later in the summer; blocks next to various kinds of dwellings most likely will be affected earlier in the season; while blocks located inside other large groups of orchards may experience only low pest pressure throughout the season. However, in every orchard, due to the ability of adult BMSBs to rapid move quickly among various hosts, a constant and vigilant monitoring program is the very basis for successful management. Commercially available traps and lures for BMSB monitoring provide valuable information to decide if insecticide treatments are needed to manage BMSB. Stink bug traps and lures from Ag-Bio and Sterling International are available for purchase and should be very helpful with effective monitoring of BMSB adults and nymphs in orchards. Although traps by themselves will not control BMSB, by capturing adults and nymphs, traps can be utilized as an effective warning system in orchards.
Factors such as different harvest dates for fruit, the mixture of cultivars, surrounding vegetation as a possible source or barrier for BMSB populations during the season, and the attractiveness of the crop to BMSB mandate individual treatment strategies for each separate orchard or block within the orchard. While some fruit blocks might require seasonal, intensive management options against BMSB, other blocks might require a less intensive program. Unfortunately, there is no "one size fits all" recipe for successful management in dealing with this pest.
Necessity of controlling other pests
In orchards experiencing continuous, seasonal pressure from BMSB, seasonal control options must be carefully selected. While selecting best control options, growers should also consider what other fruit pests and beneficial natural enemies may be affected by their selection of products used against BMSB. Detailed monitoring of all pests will be crucial in order to prevent additional crop losses caused by the "normal pests."
Planning for a seasonal insect control program
Since we currently cannot predict when BMSB will move into orchards and how intensive feeding will be during the season, we should prepare ourselves for a season-long monitoring and management program. Also, the results of our early season management activities will likely not minimize the pest pressure that fruits experience in late summer and early fall. While BMSB can cause fruit damage at any point during the season, maturing fruit likely represent the most attractive source of nutrients for this insect and, therefore, pest pressure may be the strongest in the late summer and early fall period.
Maintaining the integrity of IPM in Pennsylvania while battling the brown marmorated stink bug
Pennsylvania tree fruit growers have embraced the principles of integrated pest management (IPM) since the late 1960s and early 1970s. By one definition, IPM is the "utilization of all suitable techniques and methods in as compatible manner as possible and maintains the pest populations at levels below those causing economic injury." The goal of IPM is to minimize the number and severity of perturbations in the agroecosystem while reducing the economic, environmental, and human health costs associated with the particular management options(s).
Fruit growers in Pennsylvania are now faced with the next major perturbation and challenge to their crops and their IPM program--the invasion of the brown marmorated stink bug. The near-term solutions for BMSB will involve many different types of insecticides. Unfortunately, the most effective insecticides for BMSB control belong primarily to the chemistries of the synthetic pyrethroids, the carbamate group methomyl, the chlorinated hydrocarbon endosulfan, and a couple of the neonicotinoids. Pyrethroids and methomyl are considered broad-spectrum insecticides that are highly toxic to many, if not all of the natural enemies found in tree fruits. Because of this toxicity to natural enemies, we have only recommended the pyrethroids before bloom on apple to minimize their toxicity. Growers who have used these products postbloom on apples in the past have seen many flare-ups from European red mites, woolly apple aphids, San Jose Scale, etc.
Given the seriousness of the BMSB situation, the very high overwintering populations and that the most effective products for BMSB control are methomyl, pyrethroids, and some of the neonicotinoid products, how can growers successfully control BMSB and not completely destroy all natural enemies and the integrity of the IPM program in Pennsylvania? Growers will need to understand and employ all of the tactics used in applying the principles of ecological selectivity to this group of broad-spectrum insecticides.
Listed below are some tactics growers can use to minimize the toxicity of these products to natural enemies while still controlling BMSB.
Selection of an insecticide
All insecticides are not equal in their toxicity to natural enemies. When selecting an effective product for BMSB control, always refer to Table 4-4 in the Tree Fruit Production Guide and determine its toxicity for the various natural enemies that may also be present. Choose the product that is the least harmful to the natural enemies.
Timing of an insecticide
Proper timing is often the most effective and economical method of achieving differential insecticide selectivity for the pest/natural enemy complex. Only apply a highly effective insecticide for BMSB when they are in your orchards. Growers must be very, very vigilant to monitor their blocks and surroundings and only apply these highly toxic insecticides when BMSB is present and a threat to their crops.
The toxicity of any chemical compound is directly related to its dose. When using one of these broad-spectrum insecticides for BMSB control, always apply the lowest effective dose possible. Not only will the lowest dose likely conserve some of the natural enemies, but it will also save you some money.
Application techniques and methods
The only purpose in applying an insecticide is to kill the intended pest(s). Many growers in Pennsylvania have used the alternate row middle (ARM) technique of spraying to apply pesticides to their crops for over 40 years. We know from many years of research that this technique will provide effective pest control if done properly, but at the same time will allow for the survival of many natural enemies. Given the likelihood that the most effective control of BMSB will occur through the direct contact of the insecticide to this pest, the ARM method of spraying may be the best method to apply these broad-spectrum insecticides. By integrating low rates and frequent applications of insecticides (i.e., the original idea behind using the ARM method), better control of BMSB will likely be achieved while causing less harm to natural enemies.
Restricting an insecticide to a specific part of the tree or location within an orchard is another method to minimize the impact of toxic insecticides to natural enemies. Since BMSB is highly likely to move into orchards from the outside (e.g., woods, neighboring crops [soybeans, corn, vegetables, etc.], buildings), restricting the application of these broad-spectrum insecticides to border rows, etc., will likely conserve many natural enemies.
The brown marmorated stink bug is here and most likely will be an important and serious threat to our fruit system for a long time.
Over time, we will learn how to manage this pest more effectively. New tools such as insect behavior modifying materials (e.g., a sex pheromone, an attractant, repellent, or deterrent) will likely be required to successfully control and minimize the threat from this pest. In the meantime, with the knowledge we have and the tools that are available, we need to try to "outsmart" this pest in order to continue to produce the best quality fruits. This new, exotic pest will require new management approaches, but until we can field test some of our BMSB management hypotheses, these ideas will remain just "concepts" that may prove attractive in theory but difficult or even impractical to implement. As the growing season progresses, we will continue to "learn as we go" and provide the newest information to growers as fast as possible.
Overcoming the challenges of effective and sustainable BMSB control will not be an easy task in the near term. Much research needs to be done in order for us to develop the most effective management program for the long-term control of this pest. In the meantime, however, growers are encouraged to not lose sight of our current IPM program in Pennsylvania. We have achieved so much over the years and we have learned how to deal with those pest perturbations that seem to always occur. If we are not careful in how we manage BMSB, we may be causing many future pest problems for our industry by destroying the natural enemies that help us keep many of the other pests of tree fruits in balance.
Current and new updates and recommendations are being posted weekly during the season at the Penn State Fruit Research and Extension Center website.
Hull, L. A., G. Krawczyk, and D. Biddinger. "Maintaining the integrity of IPM in Pennsylvania while battling the brown marmorated stink bug." Pennsylvania Fruit News 91, no. 4 (2011): 9-10.
Krawczyk, G., and L. A. Hull. "Management option for the control of brown marmorated stink bug--a Pennsylvania perspective." Pennsylvania Fruit News 91, no. 5 (2011): 15-21.