The Tsuga canadensis, also known as North American spruce or Canadian Hemlock or Eastern Hemlock, is a native tree of North America, widespread in the northern United States and especially in Canada. It is a giant evergreen tree which, with its numerous foliage and branches, makes, among other things, a habitat for many species of birds, insects and many other animals.
Unfortunately, since the 1980s, these trees have been under attack from the woolly adelgida of hemlock (Adelges tsugae), a small aphid native to Japan, which does nothing but suck sugar from the needles of this tree. They can be so numerous that they can cause the death of a massive tree tens of meters high. To fight these aphids, researchers have thought well to use one of its predators, a beetle that they first bred and then released in the forests.
During a five-year study, the results of which were published in Biological Control, researchers monitored the effects of this predator on the aphids that are decimating the population of Tsuga canadensis in Canada and obtained positive results. It is mainly the beetle of the Laricobius nigrinus species, an insect the size of a grain of rice, that is crucial: it hunts adelgid eggs as well as its larvae for food.
Researchers have released several hundred thousand of these beetles at certain sites where Tsuga canadensis trees are present and have noticed that the tree populations themselves are starting to take hold again. Of course, when using techniques like this, which see the large-scale use of predators to supplant a species, there is always the risk of obtaining undesirable results, especially in cases like this where a species that is considered alien and could eventually become invasive is used.
And that’s exactly what the researchers are evaluating before starting a real mass release. The same researchers are also thinking of producing “hybrids” by making these beetles be combined with other endemic beetles from the forests where the Tsuga canadensis are present.