They occupy entire houses and cause millions in agricultural damages: Brown marmorated stink bugs are a growing problem throughout the world. Researchers are feverishly working on a solution to combat this pest – and are employing unconventional means in the process.
The brown marmorated stink bug is spreading through North America and Europe. These pests are a danger to farming, and also cause harm to human health and well-being.
Bayer researchers are searching for ways to strengthen plants’ immune systems, to ensure they are optimally equipped to repel stink bugs. Working together with entomologists, these specialists are also testing biological pest control methods, for example using samurai wasps.
Researchers are using a combination of genetic adjustments and innovative pest control methods to stem the stink bug invasion.
Countless uninvited guests are greedily ransacking the fields of American farmers. Summer marks the season in which millions of brown marmorated stink bugs traverse the country, searching for food and leaving a path of devastating damage to fields in their wake. The situation becomes increasingly unbearable for homeowners in the fall, when the stink bugs look for warm, safe and secluded spaces to spend the winter. And a stink bug is never alone – hundreds, if not thousands, frequently invade homes through tiny holes and cracks. Although they don’t cause any physical damage to houses, the sight of an army of crawling bugs covering entire walls and rooms can be extremely disconcerting. That’s why farmers and private individuals want to get rid of the unwanted guests as quickly as possible. This is no easy task, but researchers from Bayer are working on finding a solution to this problem.
Invasive nonindigenous species such as stink bugs settle outside their natural habitat and proliferate in new surroundings, thus posing a threat to biodiversity. And the stink bug’s appearance makes it resemble a creature from another world – up to 1.7 centimeters long, the stink bug has red glowing eyes, its back is protected by a shield of chitin, and it has six protruding legs which give it an unusual gait. Furthermore, the stink bug is armed: it exudes a foul-smelling odor to scare off enemies as soon as it senses danger. Although the chemical components of this substance resemble the scent of coriander, the smell is far more pungent and most people consider it repulsive.
Yet the stink bug, which originates from Asia, doesn’t just look menacing, it also poses a substantive danger to farms, particularly in the United States. “The brown marmorated stink bug has steadily proliferated since it was first introduced in the late 1990s. In 2010, for example, it caused catastrophic damage of over US$ 37 million to apple orchards on the East Coast of the United States,” explains Peter Jentsch, Senior Extension Associate, Department of Entomology at Cornell University in New York. Moreover, the latest figures are no more encouraging, as the economic losses for apple crops alone are estimated to have reached US$ 35 million in 2017. The pest has now spread throughout 44 U.S. states and four Canadian provinces. In addition, variations of the Asian stink bug have arrived all over Europe, Russia, Australia and New Zealand, thus emerging as a global threat.
Stink bugs are unpredictable and difficult to control
Combating the stink bug presents a challenge. After all, it doesn’t spread in a predictable way or proliferate according to any recognizable pattern. While there is a proven correlation between stink bug emergence, the climate and type of field crop, numerous factors remain unknown. This makes it a constant potential danger in many parts of the eastern United States. What’s more, crop protection products only have a limited effect on these pests, and various other pest control methods have failed as well. “You can never completely get rid of these bugs, but we can limit the damage with good agricultural methods and innovative research,” says Holger Weckwert, Global Segment Manager, Fruits, Vegetables and Insecticides at Bayer. He and his team are searching for ways to strengthen the plants’ immune systems, to ensure they are optimally equipped to repel stink bugs. Genetic traits represent the key to all of this. “Our aim is to introduce genetic traits to field crops such as corn and soybeans. This will enable the plants to produce substances on their own that will ward off the stink bugs and protect them from further attacks.”
It’s a difficult mission. The brown marmorated stink bug pierces the plant’s skin with its proboscis, extracting juice and nutrients in the process. Compared with biting insects, it only maintains contact with the plant for a short period of time and then quickly moves on. Therefore, the genetic traits must trigger a lightning-fast reaction. “Not only do the plants have to quickly produce the substances, they must also rapidly transport them to the area where the stink bug is piercing the skin. That’s a tremendous challenge,” says Weckwert, who is nonetheless optimistic.
Natural enemies restore balance
Even nature itself appears to be adjusting to this disparity. “When the stink bugs first arrived, they caught our flora and fauna completely off guard,” explains Michael Raupp, Professor of Entomology at the University of Maryland who has studied nonindigenous species for 41 years. “However, local predators and parasites are now discovering this new Asian delicacy in the most heavily affected areas. I refer to them – affectionately – as nature’s death squad.” One of these natural helpers is playing a major role here – even though it’s no bigger than the head of a pin: Trissolcus japonicus, better known as the samurai wasp. Just like the brown marmorated stink bug, its origins lie in China, South Korea and Japan, and it co-evolved as a natural parasitic enemy of the bug.
Looking back: The spread of a bug species
The Asian stink bug has an extremely robust constitution which has promoted its spread over the past 25 years. It has few natural enemies in North America and Europe.
This wasp systematically attacks the stink bug’s eggs and lays its own eggs inside them. The growing larvae then feed on the bug’s embryos, thus preventing them from hatching. In East Asia, the samurai wasp attacks between 60 and 90 percent of brown marmorated stink bug eggs and therefore almost single-handedly keeps the stink bug population in check.
Biological pest control could be a solution
Although the samurai wasp originates from outside North America, Peter Jentsch’s team encountered a surprise in field tests. “When Trissolcus japonicus was first detected in Maryland in 2016, we began looking for samurai wasps in high-volume farming systems where the brown marmorated stink bug had been present for the past 10 years.” By July, they had been found at an organic vegetable farm in the Mid-Hudson Valley, having already settled in the New York state region. Like the stink bug, the samurai wasp apparently made its way to the United States by accident – and there is evidence that a small population has existed in the United States since 2014. “We are now working on breeding and releasing sufficient numbers of them to keep the stink bug population in check,” says Jentsch.
Aside from all the damage and inconvenience, the spread of the stink bug has also had a positive effect. “In terms of science, the brown marmorated stink bug is one of the most productive events in the history of invasive pests in the United States,” says Raupp. The fact that the stink bug has had such a dramatic impact on the eastern United States and caught the region completely unprepared has unleashed an unprecedented wave of scientific attention. Numerous research projects, studies, seminars and congresses have since focused on the topic of stink bugs. “It was like a renaissance of entomology across all disciplines,” explains entomologist Raupp. Scientists now have a more in-depth understanding about this insect and its peculiarities, such as the fact that stink bugs prefer the edge of fields. This valuable information enables a more targeted approach with crop protection products.
Although the deployment of samurai wasps is easier than the implementation of innovative plant breeding, the genetic engineering approach has one major advantage: the overall impact on the ecosystem is less severe. Solutions are still urgently needed, as stink bugs continue to spread and cause significant damage across the United States and Europe. “As climate change progresses, the brown marmorated stink bug will continue to move north from the Black Sea region and southeastern Europe,” predicts Weckwert. A warmer climate will provide stink bugs with ideal living conditions in new regions throughout the continent. In other words, the rate at which this threat is rising is linked to the progression of climate change, and each additional degree Celsius on the thermometer.