FW: What happened to our biggest moths?

[Mike Quinn]

---FWD From Entomo-L---

Date:    Thu, 5 Apr 01 12:35:55 -0400
From:    Jeff Boettner <boettner at ENT.UMASS.EDU>
Subject: What happened to our biggest moths?


   I am coming on new to the Listserv group to help in the discussion of 
what happened to our biggest moths.  I am the senior author of the 
Conservation Biology paper (Boettner et al. 00) which is being 
discussed. If anyone would like a copy of the article, please feel free 
to email me at:  boettner at ent.umass.edu

In answer to Mike Quinn, as to what is the current N. American 
distribution of Compsilura concinnata?

    You could draw a line from ME to MN to IL to VA and back to ME and 
you would hit the main hotspots for Compsilura, however it has been 
introduced to 30 states and 4 Provinces of Canada, so it will likely 
turn up in new places. It has been introduced to areas such as WA,OR, 
CA, AZ, NM, CO, FL, and NC but most of these states have few or no 
recoveries of the fly (or, likely,  no one has looked).  It took decades 
to try to establish the fly in VA, and I suspect it will do poorly in 
the south and south west, but it is firmly established in the Northeast 
and becoming more common in the Midwest.  See Sanchez 1996 thesis ( 
Table 1.1) for a pretty complete list of releases and some recoveries.  
But these things are tough to map because of the lack of good data.  For 
example in Minnesota: Compsilura was released at Cass Lake in 1937  for 
forest tent caterpillar control and "Minnesota 1971-1977" for gypsy moth 
control .  I found one record of Compsilura in a museum labeled from 
"hawk moth larvae" Sept. 2, 1937 and then no other recoveries until 
1992, 93, 95, 97 and 98.  So Compsilura was likely breeding in 1937 but 
my guess is it didn't overwinter and the real recoveries are from the 
70's releases or from moving in from WI in the 90's.  My guess is that 
the real impact in MN will be felt during the next  years now that it 
has been recovered from multiple counties. In MA there were huge 
releases done from 1906-1913, and a handful of recoveries by 1909, but 
Compsilura was widespread by 1919.   Each state takes some detective 
work and there is always the chance someone just did their own releases, 
so official releases have to be taken with a grain of salt. .  

    Sanchez, V. 1996.  The genetic structure of northeastern populations 
of the tachinid Compsilura Concinnata (Meigen), an introduced parasitoid 
of exotic forest defoliators of North America.  Ph. D. thesis.  
University of Massachusetts, Amherst ( see Table 1.1)



    In reply to Lisa Danko that "People generally do not care about 
non-target bugs and many would rather see all insects disappear ( except 
the monarch butterfly...).  
    And reply to Peter Oboyski as to what can we do about it.

     Ironically, yesterday I got a nice letter from Paul Ehrlich at 
Stanford University and he sent me a copy of his " first publication 
ever" in the 1948 Lepidopterists' News Vol. II,  no. 8, page 92.  In the 
article he mentions that he raised " about 18 specimens of Danaus 
plexippus from larvae.  Two specimens were parasitized and the two 
parasitic flies which hatched from the pupae were sent, along with the 
pupae to Dr. C. W. Sabrosky for identification.  He identified them as 
Compsilura concinnata (Meigen)." 
      But I am not very worried about the role of  Compsilura in monarch 
population dynamics ( it has since been recovered by others as well).  
This is because although the fly is a generalist, I think it is 
primarily going to impact species in rich woods,( most of the scary 
records are for woods and edge species and not in fields).  There have 
recently been a few papers on seeing silk moth feeding in wet habitats 
on purple loosestrife.  This fits with our study.  I suspect that these 
flies have to reestablish themselves each year in wet habitats (when the 
fly tries to pupate in the wet soil, it will likely drown).  Could it be 
that cutting down more woods and making more farmland ( with thin 
windbreaks of host plants) in the Northeast would be the best thing for 
silk moths???  Too hard to tell from our work.  We never intended this 
paper to stand on its own.  The value will be finding places that silk 
moths are surviving and doing similar life tables to see how they make 
it...I suspect these areas will still have rich components of native 
flies and wasps as an indicator that the system is still healthy.  
Finding these places could be the best answer to Peters question of what 
can be done.  Unlikely Compsilura will go away since it can live on such 
a wide range of hosts.
    I doubt that silk moths will vanish from the Northeast but they may 
have a tough time in the woods.

    What got me interested in looking at the impact on silk moths was 
that I couldn't figure out where the native flies went.  I would put out 
lots of silk moths to find native flies and wasps and get mostly 
Compsilura.  So I wanted to do a systematic study to see if this was 
true at all life stages ( and in fact, I did a poor job of this because 
I still missed good collections of  the late instars, where I think 
Compsilura has the biggest impact.)  With all three species, I found no 
native flies and one native wasp.  Considering that I had been tracking 
800 Cecropia moth larvae daily, this really blew me away.  We have 
roughly 24 ( guessing) silk moths east of the Mississippi.  These 24 
moths help support 74 native parasitoids ( 54% tachinid flies, 24% 
Ichneumonid wasps,  22% Braconid and Chalcid wasps).   In addition these 
74 species in turn support 14 species of hyper parasitoids and at least 
one hyper-hyper parasitoid.  The big fear with this fly and why it is 
important to me is the bigger question of what is this fly doing to our 
native parasitoids...are we increasing diversity by adding a 90th 
parasitoid or did we really pull the rug out from some of our natives 
and lose some major diversity in the process.  It is said that for every 
species there are several parasites, so what does this mean for  the 
other 160 nontarget leps (and associated parasitoids) that Compsilura 
impacts.  I think Compsilura's impact will turn out to be much greater 
than the sum of its direct hosts... even if the host may not appear to 
be impacted.   David Almquist wrote (but I am not quoting direct): that 
you can have a lot of mortality (99.8 %) and the population of the moth 
is still stable.  This is true for the moth ( we never said the moth was 
going extinct...though lots of people have reported severe declines, and 
several species of silk moths are now state listed)...the big fear is 
for the native parasitoids.  Do we want to replace 89 parasitoids with a 
handful.  What happens when a hyper parasitoid learns to hunt Compsilura 
and we have lost the specialists?  Will we have outbreaks of silk moths? 
 All really tough questions.  

  Coming back to Ehrlich, I heard him mention once,  that the best way 
to explain biodiversity is to think of the earth as an airplane and the 
species as the rivets.  Sure we can fly without a few species - rivets.  
But everyone will have a different idea of how many rivets we are 
willing to fly without.   I guess I am one of those that prefers to fly 
with the bulk of the rivets intact.  As Donald Winsor has promoted, we 
need "equal rights for parasites."
   


George Boettner
Entomology Dept.
Fernald Hall
UMASS-Amherst
Amherst, MA  01003
413-545-1032

boettner at ent.umass.edu

 
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