Why do skipper butterflly larvae in North America heavily feed on non-native grasses?

I have been monitoring skippers in a meadow in SE Pennsylvania as part of a larger project to understand the plant-pollinator interactions in an area that is 60% non-native plant species. After looking at Lepidoptera species composition, I haven’t been too surprised to find that my meadow hosts a lot of generalists like grass skippers (Peck’s skipper, Sachem, Zabulon skipper, swarthy skipper).
But I was surprised and fascinated to learn that in their larval stage, these skippers (native to N. America) will preferentially feed on non-native European grasses like orchard grass (Dactylis glomerata) and timothy grass (Phleum pratense). I know that these grasses are basically naturalized and these grass skippers do well in disturbed old field. But they didn’t co-evolve, so I’m curious how this relationship came about. Does anyone have any insight? Other skippers seem to feed on native grasses. Could this be a case of the skippers not being “picky” and being able to occupy this niche of disturbed grassland or being just as successful as if they used native grasses? Sorry for my ignorance, I’m new to entomology.

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Maybe it is because they didn’t co-evolve? Do the introduced grasses have fewer defenses against NA grass skippers?


I think the more logical is that as slecies that already has a range of hosts, they’re adapted enough for new species of poaceae, which are all pretty close to each other in terms of biochemistry and structure, if a butterfly lives on similar native grasses, it can live on an introduced one, in urban setting where propotions of plants can be different from natural ones, insect can be found more on an introduced llant just because it’s found more often, or found more ofte were you look.


As @kevintoo implies, the native skippers have evolved in the face of an array of native grasses which we can expect to have erected (through evolutionary adaptation) at least some semblance of defense or resistance to herbivory by the native herbivores. Weedy non-native grasses, on the other hand, have a different “skill set”, adapted to rapid colonization of disturbed habitats, for instance. That may come at the cost of not retaining some of the chemical defenses their ancestral stock may have had in their native range, or more simply the defenses they bring with them (chemical, for instance) just don’t deter our North American grass skippers. The outcome for skipper larval food “preference” follows from this divergence of defensive capabilities.


Maybe low leaf Brix? if non-native spp are miss-adapted to the location and become more edible when brix drops below 12? no idea wild guess!

Thanks for a new term. I had not previously heard of “BRIX”. Interesting concept to consider.

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