Abstract: “Here, we present a comprehensive review of 73 historical reports of insect declines from across the globe, and systematically assess the underlying drivers...”
...From our compilation of published scientific reports, we estimate the current proportion of insect species in decline (41%) to be twice as high as that of vertebrates, and the pace of local species extinction (10%) eight times higher, confirming previous findings (Dirzo et al., 2014). At present, about a third of all insect species are threatened with extinction in the countries studied (Table 1). Moreover, every year about 1% of all insect species are added to the list, with such biodiversity declines resulting in an annual 2.5% loss of biomass worldwide (Fig. 2)...”
For those concerned about wild animals, such a quick rate of decline could give some reassurance (in addition to the theoretical arguments) that wild insect populations will be small in the long-run. We could have more confidence in the extent of decline if we had a better handle on any publication bias in published papers on conservation and insect populations.
Edit: Note the following comment from below from Gavin Taylor, describing the biased methodology used:
> Good point. I was commenting more on my perception of the conservation field rather than considering biases in the methodology of this study, but they keywords used were:
[insect*] AND [declin*] AND [survey]
Which [is] completely biased to finding studies showing insect declines.