West Virgina White

[hpazures at aol.com]

Dave:

Not only is Garlic Mustard a poor larval host, it is outright toxic to WVW larvae.  I've tried rearing larvae on the plant some years back when I first noted adults ovipositing on it.  First instars die within a day or two of ingesting the plant.  Trying to rear WVW's on this plant would produce the same result, though a large-scale rearing study might produce some surprises.  I'd focus on other aspects of your proposal.

I've been observing several habitats west of Washington D.C. over several years and have noted the invasion of Garlic Mustard into WVW habitat and the colonies generally collapse as soon as Garlic Mustard dominates the forest floor, even when Toothwort is present.  I might suggest studying at what point a certain density of Garlic Mustard in the habitat becomes a "tipping point" leading to collapse of the butterfly colony.  Interestingly, the Cabbage White has now become a common forest inhabitant in areas where Garlic Mustard has become the dominant forest floor plant.  

Similarly, the Falcate Orange Tip seems to be disappearing from the same areas as well but at a much lesser rate.  I don't know if Falcate Orange Tips attempt to oviposit on Garlic Mustard and die, or if Garlic Mustard is simply crowding out or out-competing native hosts.

It would be interesting to learn if someday a mutation may occur, allowing WVW's to use Garlic Mustard.  At one northern Virginia site, I collected what appears to be an intermediate phenotype between Cabbage White and West Virginia White.  Hybrid studies might be initiated to see if genes could be artificially introgressed from the Cabbage White to West Virginia White so that the WVW could utilize Garlic Mustard.  In the meanwhile, the situation does not look bright for the WVW.

The only immediate solution that I can see is introduction of an herbivore that feeds solely on Garlic Mustard - but we know how this has worked out in the past.  

Perhaps your study, if using large numbers of first instar larvae on Garlic Mustard, might be able to isolate individuals that can detoxify the plant.  I would attempt to breed these and see if those offspring can pass on this ability.  Should this happen, the butterfly could be reintroduced on a trial basis.

Good luck with your study.  Hopefully something can be learned and eventually done to help the butterfly.

Harry Pavulaan

-----Original Message-----
From: David Cappaert <cappaert at comcast.net>
To: 'CT LEPS' <CTLEPS-L at lists.yale.edu>
Sent: Sat, Apr 2, 2011 8:54 am
Subject: West Virgina White


All:
 
I sent a message recently explaining that I'm the new greenhouse/butterfly/education person at  magnet school in Hartford. I'll be in CT next week and will hope to add the occasional observation to the list. With Dave Wagner's input, I put together a concept for an investigation. Any input from the list would be welcome:
 

The problem: The West Virginia White, Pieris virginiensis, is a northeastern US butterfly with caterpillars that feed on a few brasiccaceae host species. A prime host is two-leaved toothwort, Dentaria diphylla. Like many other insect feeding specialists, the WVW uses the secondary chemistry (sinigrin) of this host plant as an ovipositional cue. The butterflies use the same chemical cue to oviposit onto garlic mustard, an invasive exotic species. Because garlic mustard is a poor larval host, this weed becomes a population sink for WVW.
 
WVW populations are reported to be in decline, at least in part due to the prevalence of garlic mustard, which grows in dense monocultures in typical WVW habitat. We propose to explore this ecological impact on the WVW by comparing adult oviposition choice and larval development on garlic mustard and native host(s).
 
Investigation: With students at the Mary Hooker School, we could set up fairly simple greenhouse and field experiments to explore insect/host interactions of the WVW. Some possible steps:

Identify sources of host plants that can be cultivated in the greenhouse. I have not found nurseries that can supply e.g., D. diphylla ... but there may be botanical gardens that could supply samples, or cuttings. Species of Arabis (A. Laevigata is a host) are available. It could be useful to evaluate other possible hosts in the brassicaceae (considering e.g., the hypothesis that meadow species of mustard plants are suitable, but unused because of habitat limitations).

Find WVW flights when they occur in the Hartford area. The CT lepidoptera mailing list would be a key resource for this.

In the greenhouse, we would monitor oviposition on plant hosts in an open vivarium, and in forced-choice tests in sleeve cages. Resulting larval growth would be evaluated in terms of stage-specific survival and growth rate.

Potted plants could be placed into field settings, and natural oviposition recorded.

Consider developing a culture so that experiments might be done in cold-season months. WVW's have a single brood, and overwinter as pupae. Could we refrigerate/freeze through a diapause period, and force early emergence?

The overall idea here would be to explore an environmentally significant question in such a way that students could help to design and run simple experiments that might be useful to science. 

 

<><><><><><><><><><><> 
DAVID CAPPAERT       
1112 Olden Rd        
Ann Arbor, MI 48103  
734-635 7750 
cappaert at comcast.net

 

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