Paul Hetzler
The Advocate
Being a descendant of Irish and German immigrants, I think it’s right to give new arrivals a warm welcome. With one exception: six-legged migrants coming ashore in North America should be viewed with a skeptical eye.
Sure, a few insects from overseas are beneficial, but that doesn’t stop them from bugging us. Asian multicoloured lady beetles (Harmonia axyridis), first imported by the U.S. in 1916 to control aphids and other crop pests, now appear in droves each fall looking for rent-free winter digs. While they do eat bad bugs and don’t actively cause harm, large numbers can find their way indoors and become a nuisance.
Some invasive species clearly harm the ecosystem, as well as the economy. The emerald ash borer (EAB, Agrilus planipennis), native to China and the Russian far east, is a case in point. Discovered in 2002 near Windsor, Ont., this forest pest is now decimating ash trees in parts of Manitoba, Ontario, Quebec, New Brunswick and Nova Scotia.
One fairly recent arrival is both a nuisance and an economic and environmental threat, a foul character indeed. Native to eastern Asia, the brown marmorated stink bug (BMSB, Halyomorpha halys) was first detected in Ontario in 2010. In 2014, BMSB turned up in an orchard in the Franklin region, in southwest Quebec, and then in the Montreal region in 2016, and is expected to spread across southern Quebec. In addition to Ontario and Quebec, BMSB is now in British Columbia, Alberta and P.E.I.
Hard to control
This pest uses a straw-like beak to suck the life out of plants, especially fruits and vegetables, bringing heartbreak to gardeners and economic losses to orchardists. Not only is BMSB hard to control with pesticides, it has no real predators. As a result, populations can build rapidly.
According to The Invasive Species Centre: “BMSB is a serious agricultural pest because its adults and nymphs feed on over 35 fruiting crops, causing damage to the fruit flesh and skin, making them unsuitable for food markets, but feeding from BMSB is not limited to agricultural crops. BMSB has over 170 confirmed non-crop hosts in North America and is a landscape-level pest that moves between non-crop and crop hosts during the growing season. Research on this pest is ongoing to determine the extent of its potential impacts as well the efficacy of monitoring, management and control options that are available.”
The term “marmorated” refers to the bands of light and dark colours around the insect’s abdomen.
Immature forms, or nymphs, change colour and shape as they moult, progressing through a series of life-stages called instars. Hatchlings (first instars) are roughly 2.4 millimetres long, with an orange abdomen and a black thorax. Second-instar BMSBs are mostly black, and instars three through five are mottled brown with one white band on each leg and antenna. Their eggs, typically found in clusters of 20-25 on the undersides of leaves, are roughly 1.6 mm long by 1.3 mm wide. Pale green at first, they later turn white, with red eye-spots developing just before they hatch.
The shield-shaped adult BMSB is 14-17 mm long, with smooth, rounded “shoulders.” It is best identified by its colour pattern, marbled brown and off-white on top with alternating bands of brown and off-white on its antennae and along the edges of the abdomen. One of the better ways to tell BMSB from similar native species is by the two light bands on each antenna. In the spring, BMSB adults emerge from mid-April to early June and feed for two weeks before mating. They damage crops in all life stages, injecting destructive enzymes as they suck plant juices.
Fruits to corn targeted
In the U.S., the “Punaise diabolique” has wreaked havoc in peach, apple and cherry orchards, especially in the mid-Atlantic region and along the west coast, with losses totalling in the tens of millions. The BMSB has also caused great harm to berry crops, as well as to corn, tomatoes and other veggies in 46 states.
But you can’t put a price on tranquility if your house is overrun with BMSB. As they become more established in an area, they seek shelter as cool fall weather sets in. In their native range (where predators keep their numbers down), they often hide under loose tree bark. But in North America, Australia and New Zealand, where nothing munch on them, populations go through the roof, and they swarm into attics and walls in such great numbers that people have swept up buckets of the stinkers.
And removing them is not fun. As their name suggests, they emit a pungent odour when disturbed or killed. They also leave enduring stains when crushed.
Unfortunately, BMSB will keep coming out of the literal woodwork over time, so the weapon of choice is a vacuum. Be advised this might make your hoover smell for a while. A shop vac that lives in a garage or shed is ideal, but taping an old nylon to the hose end creates a mini-bag where bugs get trapped and can be tossed into soapy water where they’ll drown in minutes.
Above all else, managing BMSB at home means excluding them. To that end, here are a few tips:
• Weather-strip entry doors and inspect door sweeps.
• Caulk windows inside and out.
• Rake debris and vegetation from your home’s foundation. Inspect for and seal foundation cracks.
• When insulating exposed plumbing pipes around foundation or crawl spaces, caulk small gaps and fill larger ones with steel wool.
• If you have a fireplace, screen the top of the chimney to keep out pests.
We may soon get help from the samurai wasp, a tiny non-stinging wasp native to parts of Asia. It’s a parasitoid, laying its eggs on the BMSB eggs. As wasp eggs hatch, the larvae eat the BMSB eggs.
The wasp suddenly appeared in 2019 in British Columbia, where BMSB was already a major pest. By 2021, the samurai wasp was destroying about 80 per cent of BMSB eggs. Researchers in B.C. expect that samurai wasps will naturally spread to other regions where BMSB has become established, but it will take many years for wasp numbers to catch up with pest populations. Unfortunately, the stinkers are here to stay, but there is at least one natural control agent to help keep the Punaise diabolique in check.