I don’t know exactly which sector(s) Mr Verret is talking about, so I can’t comment specifically on what he saw. But let’s still say that in general everything indicates that there are more maggots in the Quebec region than before. And yes, there is a cause for all of this…
“There are five species of insects that produce grubs that can attack lawns,” says Guillaume Grégoire, professor of phytology at the University of Laval and lawn specialist. One of these species is common and has always been there. This is the common cockchafer.
“They form large white worms, they are almost the size of a shrimp. But this beetle has a long life cycle, spanning three years. And as a rule, the damage to lawns is quite limited. »
Let’s understand here: This is clearly a so-called “harmful” insect, particularly in agriculture – particularly in corn and potato fields, according to McGill University’s “Ecological Agriculture Projects” website, but its larvae can also attack the roots of ” Grasses” like grass and cause it to turn yellow in patches. The beetle’s larvae essentially live in the ground and seek shelter up to 1 meter deep in winter to protect themselves from the cold. In summer they then migrate to the top 15 centimeters to feed on the roots – which can of course lead to the death of the plants.
However, its life cycle extends over three years and the damage is concentrated in the second year. After hatching in June, the first instar larvae feed primarily on decaying vegetation, fungi, and roots (the thin ends of roots). In August they reach their second instar and then burrow deeper into the ground. When they have completed their first winter and are in the third instar, they are at their most voracious and, of course, most devastating. The spring following the second winter marks their transition to adulthood, which prevents them from being very active – and once adult, the beetle feeds primarily on leaves, but not in sufficient quantities to cause significant damage.
Not welcome
The fact that it is only truly harmful in one year out of three significantly reduces the inconvenience that the cockchafer can cause. Aside from that, says Mr. Grégoire, there is another species of beetle that has only recently arrived in the Quebec region: the European beetle (Amphimallon majalis).
As the name suggests, it is an exotic and invasive species. It was first observed as a larva in the soil in New York State in the 1940s, which indicated active reproduction and therefore persistence, we read on the website from Michigan State University. It then gradually spread, reaching Ontario in 1959 before being observed for the first time in Quebec at Rougemont in 1986.
And he is now in the Quebec region. “I’ve been seeing them here for five or six years,” says Mr. Grégoire.
As long as its population is not too large in a given location, the European cockchafer does not pose a problem. But if it exceeds a certain threshold, from 50 to 100 larvae per square meter, our researcher specifies, then hello damage…
Because even though its larvae burrow into the ground to feed on roots, the European “cousin” does not have a life cycle of three years like the cockchafer, but of just one year. The damage caused is not “diluted” over three years, so it can be much quicker and more visible.
Unfortunately, says Mr. Grégoire, “once we see the damage, there’s not much we can do.” Even with synthetic pesticides, there is almost nothing that is truly effective. So if a pest controller tells you, “Yeah, yeah, we can do it,” there’s a good chance they won’t be able to keep their promises.
Of course, there are some biological control methods such as nematodes (microscopic worms that parasitize the cockchafer) and pathogenic fungi, “but their effectiveness depends on several factors.” [température, humidité, etc.] and therefore very variable – often even very ineffective,” he adds.
“So we have to work on prevention,” continues Mr. Grégoire. From late June to mid-July, you can turn off the lights in the house because it attracts adults [qui pondront alors leurs œufs sur le terrain]. You can also leave the grass long enough to harbor more species of insects. [parmi lesquels il y a des prédateurs de larves et/ou des œufs, ce qui va garder la population de hanneton sous contrôle]. »
Mr. Grégoire also states that he often hears that mixing clover or other types of plants in the lawn would help, but that he strongly doubts this since the cockchafer (common or European) is not a very specialized insect.
It’s possible that it prefers the roots of grasses, but it can also harbor many other plant species, and “the larvae don’t let themselves starve: if they don’t have grass to eat, they’ll take whatever is available,” he says .
Finally, we would like to add that another invasive species found in the Quebec region also produces grubs that can damage lawns. This is the Japanese beetle, but it generally causes less damage.
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