IMHO he said "taste for other plants" with tongue in cheek. Will be watching to see what more experienced butterfly people think

Monarchs would have to evolve to accept other hostplants. We already know that the 5th instar monarchs can live off things other than milkweed. That said, since we are talking about an insect that migrates, I don't see it evolving away from milkweed since part of the population is going to find milkweed somewhere. The vast majority of the returnees to Mexico will have been raised on milkweed so the few that might have found and been able to tolerate a new hostplant would not get a chance to spread their genes around. It's sorta comparable to the white monarchs. They just are not found in the migrating population.

Back in the '90s, I watched a monarch lay eggs on my hollyhock. Did not work out well for the caterpillars but it does show that some confused monarch mama will try other things even when a plethora of common milkweed was available 30' away.

Thanks roselee and kcclark.
Maybe it was tongue-in-cheek, but I think most people don't really understand the difference between nectar plants and host plants and his comment would mislead them.
Evolution doesn't happen over night, as you have mentioned.
It was just a little irritating for me to hear this local "expert" say what he did. But he's into using chemicals too, so............