The brown marmorated stink bug is making a late-season push to get ready for winter. While homeowners can expect the cilantro-smelling invasive species to invite themselves into their houses, farmers should check to see if the bugs are helping themselves to their late-season crops.
Stink bugs generally start to enter their overwintering period in mid-September, though some have been trying to get into buildings since last week, said Penn State Extension entomologist Greg Krawczyk.
Depending on the weather, they may keep coming into structures as late as November.
“It’s time for it, you know. It’s the biology,” he said.
In the winter, stink bugs enter a low-activity, low-metabolism state called diapause, which is similar to hibernation. The bugs eat nothing and can sit motionless under siding or behind a book until spring — although they may also make their presence known with their loud, bumbling flight and pungent scent.
To prepare for this prolonged period of not eating, which Krawczyk said is probably triggered by falling temperatures and shortening days, stink bugs must feed voraciously to build up the fat bodies they will live off for several months.
“Stink bugs are feeding very, very intensively right now,” he said.
The more mature stink bugs may have already built up this reserve and are the ones seeking shelter now. Some adult stink bugs are not quite ready to enter diapause, while others are still nymphs, trying to gain weight and become adults as the frost approaches.
These unready bugs are still looking to bulk up.
For much of this year, stink bugs were largely content to feed in the forests. Now, they have moved to orchards, soybean fields and patches of late-season vegetables like peppers and tomatoes, Krawczyk said.
Last year, the bugs were concentrated in the band of the state south of Harrisburg. This year, Krawczyk is fielding lots of calls as far north as State College.
Native stink bugs go through diapause like their brown marmorated cousins, but the native bugs prefer to spend the winter under bark or leaves.
Stink bugs like to feed on the most nutritious food they can find. Unfortunately, they find the same parts of plants appealing that humans do.
“Within the past three weeks or so, we’ve seen a definite uptick” in stink bugs in soybeans, Penn State Extension entomologist John Tooker said.
At this stage soybeans are well-developed, so “the impact won’t be that huge” for those farmers, Krawczyk said.
Soybeans are most vulnerable at the R-4 and R-5 stages, when the pods are filling, but stink bugs tend to hit after that process is complete, Tooker explained.
While they are unlikely to depress yields, stink bugs can still reduce the quality of soybeans. They can suck the moisture out of the seeds and make them look ugly and shriveled. Those beans will likely draw a lower price at the elevator, Tooker said.
If the weather stays warm and stink bugs start devastating crops, “farmers can still benefit from controlling them” by applying late-season pesticides, Krawczyk said.
If the mercury stays low, however, nature may be a more cost-effective deterrent than spraying, as the cold will drive the bugs indoors.
“Everything is weather-dependent from now on,” he said.
Tooker said spraying field crops for stink bugs is probably not economically beneficial at this point in the year.
“All it’ll do is make you feel better about killing bugs,” he said.
The stink bug’s distribution is patchy. They tend to be more prevalent in fields next to woods or hedgerows and less common near roads or buildings, he said.
Joanne Whalen, an integrated pest management specialist for the University of Delaware Extension, is one of the researchers collaborating from Krawczyk and Tooker on research. She said “there are definitely places” where stink bugs can still be found in her state, especially in soybeans.
The native green stink bug has historically been more of an economic problem for Delaware soybean growers than its brown marmorated cousin. Some green stink bugs have been observed in Sussex County fields this year, but they are not of much concern right now, she said.
Double-cropped soybeans are around the vulnerable stage right now, but stink bugs will likely start overwintering before they can wreak havoc in these plantings.
“Fruit folks might still worry a bit about what’s happening,” as there have been some huge catches of the brown marmorated stink bug in orchards this year, she said.
In general, though, it has been “not a huge banner year” for stink bugs in Delaware, she said.
Two websites allow farmers to report stink bugs in their area, stopbmsb.org and stinkbug-info.org.
Reporting this information can help researchers understand why the insects are concentrated where they are, Tooker said.