Another Toxic Trap

[Michael Gochfeld]

Years ago Harry Pavulaan explained to me how the explosive spread of 
Garlic Mustard may have contributed to the decline of West Virginia 
White (Pieris virginiensis), simply by outnumbering the normal hosts. 
Females would lay on Garlic Mustard but the caterpillars perished. 

I just saw an article by Jennifer Dacey (student at University of Rhode 
Island) suggesting that a similar toxic trap awaits Monarchs.  Black 
Swallowwort (Cynanchum nigrum) is an exotic member of the Asclepiadaceae 
on which female Monarchs willingly lay eggs.  It co-occurs with other 
milkweeds in New England (it is spreading, but I presume it's nowhere 
near as invasive as Garlic Mustard which is rapidly replacing ALL 
groundcover species in many central NJ forests).

Eggs laid on Black Swallowwort hatch, but the first instars die. The 
only reference I have so far is NATURAL NEW ENGLAND #5:32-33, Jan-Feb 
2001. 

On a more optimistic note, the impact of exotic plants has clearly been 
recognized by many agencies in the past five years.  Ironically, efforts 
to ban the sale of plants that are deemed noxious pests, are not always 
successful.  

Mike Gochfeld

 
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