Harmonia axyridis, the Asian Multicolored Lady Beetle
If I had to pick the most annoying insect in Illinois it’d be Harmonia axyridis. This lady beetle was introduced to our continent as a control agent for aphids but became a pest in its own right. It consumes not just aphids but all manner of other insects, including beneficials like native lady beetles. Swarms of them descend into our houses in the fall. They get just about everywhere. They have a noxious odor. And they bite.
A study out in PLoS One byLombaert et al has determined that our local beetles here in eastern North America are the culprit behind a spate of recent invasions elsewhere in the world. The researchers extracted DNA from 18 loci across the various populations, modeled several different introduction scenarios, and concluded that one story makes the observed genetic data the most likely. It’s this one:
Figure 1 from Lombaert et al 2010 showing the most likely path of introductions of H. axyridis.
The authors call this result “surprising”, but I disagree. If a pest builds to enormous numbers in a region that sees a lot of commerce, exports of that pest may become much more likely than exports from the native range. Especially if native populations are kept down by predators and competition.
We see this in ants all the time. The invasive Argentine ants in California arrived from an earlier invasion to the eastern U.S., not as a separate colonization from Argentina. Fire ants in Australia appear to be from the United States, not South America.
In any case, it’s an interesting and timely study. Now, if they could just figure out where I can send the beetles in my house so they don’t come back, that’d be really valuable.
source: Lombaert E, Guillemaud T, Cornuet J-M, Malausa T, Facon B, et al. 2010 Bridgehead Effect in the Worldwide Invasion of the Biocontrol Harlequin Ladybird. PLoS ONE 5(3): e9743. doi:10.1371/journal.pone.0009743
There’s been a debate simmering among 
Myrmecos Blog 