> Do we in fact know of any insect-pollinator species that have gone extinct (not merely been listed as threatened or endangered) in the last hundred years?

For openers:

In Hawaii ... although over 5400 species of insects are known from the archipelago (Nishida 1994; Stein et al. 2000b), entire groups of potential pollinating insects have been driven into extinction. Fifty-two species of endemic bees in the genus Nesoprosopis and 26 species of endemic moths in the genera Agrostis, Hedylepta, Nesopeplus, Scotorythra, and Tritocleis are now extinct, and many other species of potential insect pollinators are endangered. 

In sum, the frightening picture of pollinator disruption that emerges from oceanic islands is one of reciprocal extinction of entire pollinator sets and the plant guilds that support them.

Pollinator Extinction in the Pacific Islands
Author(s): Paul Alan Cox and Thomas Elmqvist
Source: Conservation Biology, Vol. 14, No. 5 (Oct., 2000), pp. 1237-1239

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