Nov 27, 2013

Researchers seeking strategies for the brown marmorated stink bug

The brown marmorated stink bug (BMSB) is a severe economic threat to fruit and vegetable growers, especially in the mid-Atlantic states where it first took hold. The invasive pest – accidentally introduced from Asia in the 1990s – caused an estimated $37 million in losses to the U.S. apple industry in 2010. As of May 2013, it had been detected in 40 states, according to USDA.

Researchers across the country are studying ways to manage BMSB. Much of their efforts are linked together by a USDA-funded project (described on its website, StopBMSB.org), but discoveries are being made in other areas, too.

Pennsylvania

Greg Krawczyk, a tree fruit entomologist with Penn State University and a co-director of the StopBMSB.org project, discussed BMSB in July, during a grower field day at the Penn State Fruit Research and Extension Center in Biglerville, Pa.

In 2009, the average Pennsylvania orchardist had a pretty good management system, Krawczyk said. He (or she) usually didn’t have to apply insecticide more than five times after bloom. Thanks to mating disruption and other techniques, less-selective insecticides only had to be used in emergency situations. Fruit quality was high, and beneficial insects were protected.

Unfortunately, the system fell apart in 2010, when BMSB first attacked Pennsylvania fruit on a large scale. Seeing how much damage the invasive species could do to orchards was a “shocking discovery,” he said.

“If you had asked any entomologist in the state, in 2009, for a list of the 10 most important stink bugs, I bet nobody would have listed BMSB,” Krawczyk said.

BMSB is now No. 1 on the list, and the average Pennsylvania fruit grower is now spraying more than double what he sprayed in 2009. Certain insecticides – carbamates, some neonicotinoids, some pyrethroids – can kill BMSB, but only if the bug is in the orchard, he said.

Unfortunately, it’s not always in the orchard.

Krawczyk and his team now spend about 90 percent of their time studying BMSB. Working with researchers around the country, they’ve figured out a few things about the invader’s behavior.

BMSB is unlike any other insect they’ve dealt with. It doesn’t spend all of its time in the orchard. In fact, it likes to overwinter in places like houses, barns, sheds, attics and garages. When the bugs come out from their winter shelters, they’ll feed on any green plant that is around, including many trees. The adult bug will feed on more than 200 host species, many of which it finds more attractive than fruit crops, Krawczyk said.

But it will feed on fruit crops – and lay eggs. Adult bugs can move into orchards, feed, lay their eggs and leave without being seen. When the eggs hatch, the nymphs will feed on fruit and foliage for the next six weeks. That’s what really damages the orchards, he said.

The insect’s mobility is what makes it so difficult to control. You can spray your orchard many, many times, but even if you hit the bugs that happen to be in there, others can come from just about anywhere. Pennsylvania farms occupy less than 20 percent of the state’s total acreage. The stink bug can go anywhere in that remaining 80 percent to multiply, and nobody outside a farm has a vested interest in trying to control it, he said.

BMSB doesn’t appear to have developed much resistance to insecticides yet, but that’s probably because the bugs keep coming into orchards from different locations. And the products that are effective against BMSB are very toxic to beneficial insects. All in all, spraying probably does more harm than good, he said.

Krawczyk and his team are trying to develop alternative ways to manage BMSB, but it’s not easy.

“The important part is ‘trying,’” he said.

Krawczyk would like beneficial insects to be the chief means of controlling the invader, but most of that control would have to come from outside the orchard. By the time the stink bug is in the orchard, the damage has already been done.

Unfortunately, beneficials haven’t shown much of a preference for BMSB. Spiders, lacewings and preying mantises are known to eat the bug, but being generalist predators they’ll eat anything. BMSB spent 15 years developing in areas where no pesticides were applied, but predators in those areas weren’t effective enough to stop its growth. Some parasitoids seem to be adapting to BMSB, but it could be years before they have a significant effect on the invader’s population, he said.

In the meantime, Krawczyk and others are studying other management strategies: behavioral approaches based on pheromones; placing nets on deer fences; a combination of light and insecticides.

Like all insects, stink bugs are attracted to light. Light traps can collect hundreds or thousands of the bugs in a single night, but Krawczyk isn’t sure if that makes much of a dent in the population.

Organic

Another USDA-funded project is studying BMSB management in organic farming systems. Anne Nielsen, a fruit entomologist at Rutgers University, is the project director.

Nielsen’s project focuses on the needs of certified organic farms first and foremost – though its findings could also be applicable to conventional or IPM management strategies. The project covers 12 states but is centered on farms in the mid-Atlantic region, where BMSB is at high levels, Nielsen said.

Since organic farms in the mid-Atlantic grow a diverse array of crops – and since BMSB eats just about everything – the organic project takes a whole-farm management approach as opposed to a crop-specific approach, she said.

Nielsen and other researchers are studying several management tactics. They’re trying to find patterns in the way BMSB nymphs and adults move throughout a farm and in the way they choose host plants. They’re also looking at trap cropping – planting an attractive host plant that will keep the bug away from a cash crop. Sunflowers and red sorghum seem to have potential as BMSB trap crops. Both crops are tall, have edible seeds (a good source of protein) and are brightly colored, which could provide a visual cue for the bug, Nielsen said.

The organic project, which started in 2012, also is studying the impact of native parasitoids and parasites on BMSB. So far, the researchers have found higher levels of native predation and parasitism on BMSB than they expected. They’re still analyzing the initial data, but they’ve found that katydids, lady beetles, some parasitoid wasps and a sucking predator they haven’t identified yet are affecting BMSB’s population. The results are encouraging, but the predators aren’t yet providing sufficient levels of control for an effective management program, she said.

To visit the project website, go to eorganic.info and click on “Brown Marmorated Stink Bug in Organic Farming Systems” in the upper right corner.

– Matt Milkovich