Check done: fewer insects than before?

“In recent years, I found a lot less insects in my pool than 10 years ago. And it’s even more marked this year: for example, I have not seen any bumblebee [or perhaps one] until now. Is it circumstantial? We say that not in the media, that the decline is real and dramatic, but is it a fake news? “Asks Philippe Boulanger, Lévis.
FACTS

It is especially since 2017 that the media speak (a lot) of a massive and widespread decline of insects, in the wake of a German study that concluded that the biomass of insects (the total weight of all insects combined) fell by as much as 76% in protected areas in Germany in less than 30 years. Other works of the same kind have subsequently been published. Last fall, for example, a study published in the PNAS indicated that insect traps in the rainforest of Puerto Rico caught between 4 to 8 times fewer insects (by weight) in 2012, or even 10 to 60 times less depending on the type of trap, than the same traps laid in the same places in 1976. And a review of published literature this spring also concluded that globally, insect biomass decreased by about 2.5% per year on average.

In short, there is indeed legitimate and very disturbing data about the fate of six-legged wildlife. But there are some small (and big) points to highlight here.

First, the media coverage of these studies has taken a totally apocalyptic tone. Some have even mentioned the “disappearance of insects within a century”, which entomologists have described as gross exaggeration .

Second, and most importantly, the data available on insect populations may be very dark, but they are still very, very fragmentary. “I think there is too little reliable scientific data, widely distributed geographically, and continued long enough to conclude the general decline of insects,” said researcher in entomology Laval University Conrad Cloutier. Université de Montréal’s insect collection coordinator, Étienne Normandin, agrees, and many other entomologists around the world have launched the same message over the last few months: the numbers we have are alarming, but very insufficient.

First, there are too many areas of the world where insect abundance has not been studied, or so little – the literature review published in the spring, for example, has identified only one study for all of Australia and only one for China. Then there are far too many insect species for which there is no data: only about 20% of the estimated number of insect species on Earth is known.

“The money from entomology research is concentrated in critical areas where insects can have a big impact, such as forestry and agriculture. This is normal because pests can cause billions of dollars in economic losses, “says Normandin, but it also leaves big” holes “in the overall picture of insect populations.

In addition, he continues, if the decline is absolutely undeniable in the case of many species, it does not mean that they leave an empty space behind them. “What happens is that we observe a homogenization of insect species. For example, I did a study on the bee species present in the city, and there are a handful that are very well adapted. Even when we look at environments that are just slightly urbanized, these species are doing very well. But species that are more specialized or less adaptable, they are lost, “he says. From the point of view of biomass, therefore, the disappearance of a species does not imply that the sum of insects “weighs” less than before. (Even if it’s still a loss of diversity, of course.)

One word, finally, about the bumblebees, since Mr. Boulanger uses it as an “indicator”, so to speak. “It’s at least the fifth person who mentioned me [the absence of bumblebees] this year, so maybe something has happened,” says Normandin. It is possible, he says, that the cold spring we have known is involved.

But now, Mr. Cloutier, who also lives on the South Shore of Quebec, but in the countryside, does not feel to have seen less drones than usual this year. If Mr. Boulanger sees less and less bumblebees (and other insects) in his pool for 10 years, it is perhaps because Lévis is developing at a high speed, suggests the researcher. One can imagine, he says, that ten years ago Mr. Boulanger’s neighborhood was close to agricultural areas or “wild” enough for insects, which then landed many in the pools. But as the city has grown, these areas have been urbanized, so the more insect-friendly areas are now further away from Mr. Boulanger’s property.

More generally, the situation of bumble bees is similar to that of other insects: we have data that prove the decline of some species, and even that suggest a general decline , but we are still far from having the proof, says M Cloutier.

Not clear. Much of the available evidence suggests that there is indeed a decline in insects, but they are not abundant and robust enough to prove it convincingly. Maybe it will come one day, but we are not there.

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