My background is in ant ecology, but I have had general entomology training. I can find some references for you in a few hours.

Edit for more compelling evidence:

a famous example of rapid evolution though, variation must exist for selection to act upon, so small populations are at greater risk given that they are likely to have much lesser genetic diversity.

Here is an example of mutualism breaking down as the result of environmental change (herbivore exclusion). While this is specific, it highlights that mutualisms once thought to be tightly bound may be more or less plastic, resulting in further change in community assembly, which is probably one step in a series.

I believe a major hurdle, explained best in this article, is that we simply do not know the full extent of insect diversity. The key points are that the biggest factor affecting insects is shared by plants and vertebrates alike: ecosystem change.

To return to the original question: are we past the tipping point? For insects as a group, they are super numerous and occupy a tremendous variety of niches. Insectes isn't going anywhere. Admittedly there is a cascade of declines are already in the works, similar to other vertebrate groups.

tl;dr - Reliable estimates of insect extinction are very hard to quantify at this stage, but the biggest factors causing decline in insect abundance are largely the same as those for vertebrates and plants. The best way to preserve that which we don't understand is not to change it in the first place.