As someone who has been working on the population biology of purple
loosestrife (especially colonization genetics), I have been following this
exchange with interest.  Below is a list of relevant sources of
information.
 
Basically, we don't know too much about the population ecology or
colonization biology of this species.  There is very little scientific
evidence that it is as nasty as it's supposed to be but certainly no
empirical evidence to the contrary.  However, there is a strong feeling
among people who work in wetlands (including muself) that it is a VERY
aggressive plant and can drastically change the species composition of
wetland vegetation in a very short time.
 
The biological control program appears to be well planned and there has
been fairly extensive tests done on the three principal insects.  They ARE
fairly specific to purple loosestrife, and would appear to be quite
appropriate for the job (i'm no bio-control expert).  While they do feed to
some extent on other loosestrifes and other members of the Lythraceae,
these other taxa are probably in greater danger from purple loosestrife
competition than from the bio-control agents.  I agree with one of the
previous contributors that we will not be successful in wiping out this
species.  Genetically, it is a very poor candidate for complete
erradication.
 
Beekeepers will be particularly interested in the cost/benefit analysis of
loosestrife control (including the cost to beekeepers) presented in
Thompsopn et al. (1987).  In Ontario, purple loosestrife is visited by both
honeybees and Bombus spp.
 
I hope this information is useful.  As a final note, the root of the purple
lossestrife problem is probably wetland disturbance and habitat
degradation.  This species thrives in disturbed wetlands. If we want to
control its spread, we should concentrate on controlling our own impact on
wetland habitats.
 
Thompson DQ, Stuckey RL, Thompson EB. 1987. Spread, impact, and control of
purple loosestrife (Lythrum salicaria) in North American wetlands. U.S.
Fish and Wildlife Service. NTIS, 2.
 
Stuckey RL. 1980. The distributional history of Lythrum salicaria (purple
loosestrife) in North America. Bartonia 100: 3-30.
 
Ottenbreit KA, Staniforth RJ. 1994. Crossability of naturalized and
cultivated Lythrum taxa. Canadian Journal of Botany 72: 337-341.
 
Mal TK, Lovett-Doust J, Lovett-Doust L, Mulligan GA. 1992. The biology of
Canadian weeds. 100. Lythrum salicaria. Canadian Journal of Plant Science
72: 1305-1330.
 
Malecki RA, Blossey B, Hight SD, Schroeder D, Kok LT, Coulson JR. 1993.
Biological control of purple loosestrife. BioScience 43: 680-686.
 
 
Christopher Eckert
 
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