By Jessica Fraser, PhD student at l’Université de Montréal
Picture a lady beetle. Did it look like this?
That’s Harmonia axyridis, a very common sight in Québec. It goes by many common names: harlequin lady beetle, Asian lady beetle, multicoloured lady beetle, and perhaps a few angry “nicknames” that it’s best not to include here. When I’m talking about it in the context of my research, I usually just call it “Harmonia.” Despite its lovely name, many people have a relationship with this species that is anything but harmonious.
If you know one thing about H. axyridis, it’s probably that this species is invasive in many regions around the world, and Québec is no exception. While we know it as a nuisance now, it was originally expected to be helpful in its introduced range. People often express concern about classical biological control, that is, the deliberate introduction of an exotic natural enemy to control an exotic pest, because they worry that the newly introduced natural enemy will cause problems of its own. I find that when people cite examples of classical biological control agents that have run amok, it’s usually either the cane toads introduced to Australia to kill sugarcane pests—which was done 90 years ago with none of the rigorous safety testing required today—or, for a local example, H. axyridis introduced to North America to control aphid pests. While H. axyridis has been deliberately released several times over the years, the story of its establishment here is somewhat complicated.
H. axyridis made its way to Canada from the United States. The first deliberate release of H. axyridis in the United States took place in 1916, but the early introductions don’t seem to have worked. More releases took place into the 1970s and 1980s, until the beetle was finally detected in the wild in 1988. From there the population took off, spreading quickly and reaching Canada by 1994. Some researchers argue that the US populations all stem from a single introduction event, and it’s not clear whether this was from one of the deliberate releases or from an accidental introduction. Of course, even if the one introduction that stuck was accidental, it’s the thought that counts. If we’re making a list of “regrettable ideas in classical biological control,” it’s not exactly difficult to make the case that H. axyridis belongs on it. These days, we prefer classical biological control agents that only attack a narrow range of prey or hosts, as opposed to generalist predators like H. axyridis, because we worry a lot more about the risks to non-target species. H. axyridis does actually control some aphid pests, but this comes at a cost. It will happily eat native non-pest aphids as well as native lady beetles and other native aphid predators, and it competes with native predators for prey. In some ecosystems, its arrival correlates with declines in native aphid predators.
Perhaps more noticeably for the average person, it’s annoying. It likes to sneak into houses to pass the winter like the world’s worst roommate: staining furniture and carpets, biting the other residents, being stinky, and refusing to pay rent.
The biting comes from its search for food, and is unpleasant but harmless (unless you’re unlucky enough to be allergic). The stink and surface staining come from a defense response. When it’s in danger, H. axyridis—like many lady beetles—will bleed a stinky, bitter fluid to deter predators. This is a neat trick, but on top of the staining, it causes us other problems. In autumn, the beetles like to feed on the sugars from berries, including grapes. When the grapes are crushed into wine, the beetles can get swept up into the mix, blending in all those unpleasant predator-deterring flavours. Most wine-drinkers don’t enjoy the aroma of “asparagus” or “spoiled peanuts,” or so I’m told. In defense of the beetles, I don’t think they’re any happier about this situation than the vintners.
I’ve been fortunate enough to get personally acquainted with H. axyridis in the course of my PhD research. I’ve learned that for those who wish to establish a colony of H. axyridis, there are a couple of challenges to watch out for. The first is parasitism. Dinocampus coccinellae is a tiny parasitoid wasp that lays its eggs in adult lady beetles. The parasitoid larva slowly consumes non-vital parts of its host’s body. Once it has developed sufficiently, the parasitoid emerges to pupate underneath its host. By this time, the eviscerated but still-living beetle has been manipulated into standing guard over the pupa, protecting it from any attackers. If one of these wasps finds its way into your lady beetle colony, it can treat it as an all-you-can-parasitize buffet. Fortunately, lady beetle eggs are safe from the parasitoid, so you can collect those and start a new, uncontaminated colony.
The second problem is cannibalism. Like many lady beetles, H. axyridis will gleefully consume its own species, and the larvae in particular need to be kept at low densities with plenty of food to discourage this behaviour. Eggs also need to be protected from larvae and adults alike. The cannibalism and general viciousness make me wonder why lady beetles are considered one of the few “cute” groups of insects. I would nominate weevils for the honour, but I don’t make the rules…
You might wonder why I bother with a cage full of H. axyridis at all. My research concerns the use of flower strips to control aphids in lettuce fields in Québec by promoting natural enemies. This strategy has proven effective in California, but of course there are some differences between Québec and California. While climate might come to mind first, the insect communities also differ between these two lettuce-growing regions, and one major difference is the abundance of lady beetles. Researchers in California reported very few lady beetles in their lettuce field surveys, but here in Québec, we find massive numbers of them, with H. axyridis as the dominant species. I want to know what exactly it’s doing in the lettuce. Obviously, it’s eating aphids, but which aphids? Not all aphid species are equally detrimental to lettuce growers.
I was fortunate to have the opportunity to present a portion of my research on the foraging habits of different aphid predators—including H. axyridis—this summer in Tours, France, at the International Entomophagous Insects Conference thanks to a travel scholarship from the QCBS. Through my ongoing research, I hope to discover what role H. axyridis plays in Québec’s field lettuce production, as well as gaining a broader understanding of the ecological factors—such as predator community composition—that contribute to the success or failure of flower strips as a method of biological pest control.
About the Author:
Jessica is working on her PhD supervised by Jacques Brodeur at the Université de Montréal and by Annie-Ève Gagnon at Agriculture and Agri-Food Canada. She studies the use of sweet alyssum (Lobularia maritima) flower strips in conventional lettuce fields in Québec to control aphid pests, and ecological interactions that may influence the flower strips’ efficacy. She has never tasted beetle-tainted wine, and hopes she will never have to.
Super cool! Your research is fascinating and important. I’ve always had vaguely worried feelings when seeing ladybugs because of not being sure whether they were the invasive kind or not. (I also agree that weevils are quite cute- though I propose leafhoppers are also strong contenders). At any rate, thank you for your work on this!