They’re on walls. They’re on ceilings. They’re on cups left in cupboards and anything left outside.
If you’re in south-central Manitoba and feel something crawling on your arm, chances are it’s a lady beetle.
The annual swarm is nothing new to rural Manitobans during September and October, but populations are particularly hearty this year with an upswing in aphids, the insects’ main source of prey.
Aphids were a repeat concern in the province’s weekly insect and disease reports. The pests were noted in cereals, peas and soybeans, with some fields tipping over economic thresholds.
Many of those concerns centred around central Manitoba. In mid-July, the region noted high aphid levels in cereals, while soybean aphids became a growing issue into August.
In late July, counts in fields near Portage la Prairie broke over 250 soybean aphids per plant and some farmers turned to pesticides. By August, the province noted predators were increasing in response, including multicoloured Asian lady beetles, according to Manitoba Agriculture entomologist John Gavloski. The non-native species is the main culprit in Manitoba’s yearly fall invasion.
While there have been no specific counts, Gavloski noted a marked jump in this year’s lady beetle surge.
“I don’t think it’s that we haven’t had high levels of lady beetles the way we now do,” he said. “I think we’ve had those high levels previously, but what’s different is the multicoloured Asian lady beetle, when it comes time to get ready for overwintering, instead of crawling underneath a leaf pile or something like a lot of our native species will, they’re looking for a sort of isolated structure on the horizon to use as an overwintering site.”
The species overwinters in cliff cracks and crevices in their native eastern Asia. In the largely flat Prairies, however, human structures are often the nearest substitute.
“What happens is they congregate in these huge numbers around or on the walls of houses this time of year and they’re looking for, of course, a way that they can get in where they can overwinter, so it becomes very noticeable,” Gavloski said.
For rural residents, it’s become a fall tradition, albeit one with mixed feelings.
Lady beetles are an undisputed boon for farmers, who value the predatory insects as a natural biocontrol for pests.
The beetles are best known for their voracious appetite for aphids, although moth or beetle eggs, thrips, mites or, for some of the province’s 66 species, nectar and pollen, may also make it on to the menu, according to Manitoba Agriculture.
A Manitoba-based study in the ’70s found that an adult 13-spotted lady beetle may eat between 110 to 160 aphids a day in cereal crops, while studies out of Ontario suggest the seven-spotted lady beetle may take out between 80 to 115 soybean aphids daily, depending on gender. The insect’s larvae are almost as useful. The same Ontario studies found that a third-instar seven-spotted lady beetle larvae will eat 105 aphids each day.
For the multicoloured Asian lady beetle, a 1970 study in Asia estimated that larvae eat between 90 to 370 aphids, depending on aphid species, while adults will eat between 15 to 65 aphids per day.
“Loved seeing them in our soybean fields eating aphids,” Ian Steppler, who farms near Miami, said over social media.
Others are less welcoming, largely because, unlike their native counterparts, the multicoloured Asian lady beetle has been known to bite.
The species also shares one of the lady beetles’ common unpleasant traits, releasing a smelly, staining liquid when threatened or injured.
Keep them out
There are few options for residents irked by the insects, Gavloski said, although residents can limit beetles inside the home by sealing wall cracks, using weather stripping around windows and vents and vacuuming up those that get in.
“Don’t squish them, because they will stain and they will smell,” he warned.
Are they pushing out native species?
Introduced lady beetles are a double-edged sword for experts like Gavloski, who note their incredible appetite for yield-destroying bugs while also marking a shift in lady beetle population, one that has increasingly phased out native species.
There is no data on how much native species account for this year’s spotted insect surge. Anecdotally, however, Gavloski noticed that most beetles near Carman are either multicoloured Asian lady beetles or seven-spotted lady beetles, both introduced species.
The native 13-spotted lady beetle, on the other hand, was thin on the ground.
“I would prefer, as far as generalist predators go, to let the native species remain the dominant species and do the work,” he said. “Now, on the positive side, multicoloured Asian lady beetles are a very aggressive lady beetle with, for a lady beetle, a pretty broad appetite and they eat a lot. They’re actually a very good biocontrol agent.”
The species was never intentionally released in Manitoba, Gavloski said, countering the common view that farmers initially brought in the bugs for pest control.
The species was purposefully released in both the United States and Canadian Maritimes through the ’80s, although entomologists now also say that trade may have played a role. The beetles arrived accidentally at several seaports before the first major population was discovered in Louisiana in 1988. The bugs have since spread into Manitoba.
Gavloski noted that the influx has not put a significant dent in aphid populations.
“Lady beetles do have their impact,” he said. “That effect may be seen down the road, but aphids reproduce so quickly. There’s been that causation between aphids and their natural enemies over the eons and the aphids can still build their populations up despite the lady beetle numbers.”