FW: What happened to our biggest moths?
Mike Quinn
Mike.Quinn at tpwd.state.tx.us
Tue Apr 10 15:22:58 EDT 2001
---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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