Obviously you can't. I am surprised they don't claim the number of mosquitoes is up (I have heard them claim Malaria was going to increase) but the number of approved bugs like bees are declining. All bugs declinining is nonsense and it can be demonstrated by a simple thought experiment. Insects have the ability with the large number of eggs to easily catch up in population if for any reason there was a decline (which hasn't been demonstrated IMO) and so why doesn't it?

Obviously there may be many species that are being eliminated in the tropics as forests are torn down to grow bio fuel crops etc. To suggest there is a decline in number for any given square mile of wilderness (for example) is sophistry which seems to be their implication and you really have to wonder why anyone would fall for it.

You do samples, in representative environments.

And recognize how many acres of those environments have changed.

When you're talking gazillions of bugs, you don't worry about an error of a few billion.

Many decades ago, the accountant of a large bank on the west coast, said that he realized he was dealing with a lot of money when, in his financial statement, he realized he was rounding off the dollars to the nearest million. ;)

This is a cumulative effort from the thousands of entomologist worldwide who collect these arthropods and study them. They are even further broken down into genus and species, and where they are found, as well as number of specimens. Much is estimate for a given region.

As for the decline in populations, this is something I have observed myself, and this season, I even wonder where all my spiders have gone. Even the frogs are disappearing.

Well okay it is obvious that you cannot have an increase in numbers of one species (humans) without affecting and decreasing other species.

But come on TIPPING POINT what exactly does that mean, and sixth extinction event, that is pure alarmism,

This is the kind of paper where they can basically say whatever they want, and it not possibly to confirm or deny it.

I think you are trying to read too much into this. The abstract starts with: "... anthropogenically driven biodiversity loss ...". It therefore qualifies as an "on message" paper. No dissent or questioning is, therefore, allowed.

We do not even know the number of insect species never mind the number of individual insects.

It could be like the polar bear problem. Initially they only noticed the numbers in a small area declining. It was only later they realised that the bears had just wanted a change of (all white) scenery and they had moved. Still, it was another paper published, another scary press release and many related headlines. What is not to like?

EDIT: The reference below gives the total mass of humans as about 350 million tons. The map below is from Google Maps and is of the area round the Eifel Tower in Paris. The black square represents the base of a box which if it were tall enough to house the Eifel Tower would be big enough to contain the entire population of the earth.

Many estimates suggest that there are more ants and termites, in terms of biomass, that there are humans.