Pierie virginiensis - host plants and threats from exotic mustards

[Shueyi at aol.com]

Leppers---

Last week I the oppurtunity to to hike several state-owned and Nature
Conservancy preserves in southern Indiana.  Two of the sites were deeply
entrenched valleys through mesic decidious forest .  Not  surprisingly, P.
virginiensis was pretty common at these sites, as both communities supported
abundant stands of Dentaria in the creek bottoms, the typical host.  However,
both sites also supported sparce stands or Arabis lavigata on the drier
slopes.  Knowing that we found P. virginiensis using this host on a
preferential basis at one site in Ohio, I checked out the Arabis.  Almost
every stem had 1 or more eggs on it, while I could not find any eggs on
Dentaria (but keep in mind that there were thousands of stems of Dentaria at
each site and I checked 20 or so plants at the most).

Thus it would appear that using Arabis is more widespread than previously
thought, and that Arabis (which is about 5X taller than Dentaria) is a very
attractive target for ovipositing females.  

I also spotted a single garlic mustard plant at one of the sites (an
agressive exotic which we always remove when we find it in a preserve), and
it had over 10 eggs on it!  Most reports say that this European mustard
species has too much mustard oil in it for North American Pieris, and is
toxic to larvae.  Garlic mustard is a huge visual target for ovipositing
females, Standing taller than Arabis and with broad leaves (very slender
grass-like leaves on Arabis).  

If Garlic mustard is indeed toxic to P. virginiensis larvae, and presents a
super-attractive oviposition substrate (both visually and chemically) to
females, could garlic mustard invasion into forest systems effectively
wipe-out populations of this localized butterfly?



Just a question to ponder from,

John Shuey