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BEN # 190

Adolf Ceska aceska at VICTORIA.TC.CA
Sat Apr 25 11:34:28 EST 1998

BBBBB    EEEEEE   NN   N             ISSN 1188-603X
BB   B   EE       NNN  N             
BBBBB    EEEEE    NN N N             BOTANICAL
BB   B   EE       NN  NN             ELECTRONIC
BBBBB    EEEEEE   NN   N             NEWS

No. 190                              April 25, 1998

aceska at victoria.tc.ca                Victoria, B.C.
 Dr. A. Ceska, P.O.Box 8546, Victoria, B.C. Canada V8W 3S2

From: SDELONG at mfor01.for.gov.bc.ca

BOTANY  BC is still in the planning stage and it's scheduled for
June 18-20 in the Peace  River  area  (Fort  St.  John).  Focus:
Vegetation  of the Peace River Breaks and Wetlands. We can still
change the date and other possibilities are June 21-23  or  July
9-11.  I  would greatly appreciate if you could e-mail me if you
have a strong preference as to date. Please, answer directly  to
me. Craig Delong <sdelong at mfor01.for.gov.bc.ca>

From: Cris Guppy <cguppy at quesnelbc.com>

The pesticide which poses the most serious threat to the conser-
vation  of  rare butterflies and moths is the otherwise environ-
mentally friendly bacterial insecticide Bacillus  thuringiensis,
commonly  known as "Bt". Bacillus thuringiensis occurs naturally
in the soil and on plants. Different varieties of Bt  produce  a
crystal  protein and spores that are toxic to specific groups of
insects. Bacillus thuringiensis variety kurstaki (Btk) is  espe-
cially toxic to pest species of butterfly and moth caterpillars.
Other varieties of Bt include variety tenebrionis for control of
Colorado  potato  beetle  and  elm  leaf beetle larvae, var. is-
raelensis for control of mosquito, black fly,  and  fungus  gnat
larvae,  and  variety aizawai for control of wax moth larvae and
various caterpillars, especially the diamondback moth  caterpil-

When  Btk is eaten by a caterpillar, the crystal protein and the
spores damage the gut lining, leading to gut  paralysis.  Cater-
pillars  stop  eating,  become limp and shrunken, die and decom-
pose. The crystal protein in commercial formulations of  Btk  is
only  toxic when eaten by insects, such as caterpillars, with an
alkaline gut pH and gut membranes sensitive to  the  toxin.  The
caterpillars  must be at a susceptible stage of development, and
the Btk must be eaten in sufficient quantity. Caterpillars which
eat doses of Btk too low to kill them may  produce  adults  with
reduced  reproductive  capability,  sometimes resulting in addi-
tional population reductions the year after spraying.

Btk loses  its  activity  shortly  after  application.  Sunlight
breaks  down  the  crystal  protein  and  rain washes it off the
foliage. Within a few days to a week the Btk is  no  longer  ac-
tive.  Information  regarding Btk to about 1991 is summarized by
Otvos and Vanderveen  (1993).  Btk  kills  caterpillars  of  all
butterflies  and  moths,  although  some  species  are partially
resistant to it.

Young larvae are usually most susceptible to Btk, but fourth and
fifth instar larvae eat greater volumes of leaves and  therefore
have a greater chance of ingesting Btk when the application does
not  achieve  even  coverage.  Any  caterpillars  feeding on the
outside of leaves, which includes most butterfly and moth cater-
pillars, will be affected when Btk is sprayed. Garry oak ecosys-
tems sprayed with Btk show significant reductions in both  over-
all  number  of  all butterfly and moth caterpillars (50% reduc-
tion) and in species  diversity  (38%  reduction).  Three  years
after  the  application species diversity was still depressed in
the Btk treated area, although overall caterpillar abundance had
recovered (Miller 1990). Ceanothus shrubs sprayed with  Btk  had
an  81%  reduction  in caterpillar abundance soon after spraying
had occurred, and there was still a 71% reduction  at  the  same
season the next year. Uncommon caterpillar species were the most
adversely  affected, with uncommon species being completely lost
from the area treated with Btk (Miller 1992). In coastal British
Columbia even small populations of Gypsy  Moth  are  effectively
eliminated  by the Btk. Any other rare butterfly or moth species
with caterpillars feeding on leaves at time of  Btk  application
is also likely to have significant population reductions and may
be  extirpated.  Rare species of butterflies and moths have poor
dispersal ability, poor colonization ability,  and  low  popula-
tions,  and  many  of  them  will have larvae present at time of
spraying. Their small populations will also be extirpated by Btk
spraying. Gypsy Moth is an excellent colonizer, and will soon be
back.  Butterflies  and  moths  of  conservation   concern   are
generally poor colonizers, and may not have any populations from
which  re-colonization  can occur, and will have been extirpated
forever. Control of pest lepidoptera through Btk spray  programs
will  therefore  almost  inevitably  severely impact, and likely
extirpate, many of the lepidoptera of  conservation  concern  on
southern Vancouver Island. This process may take decades, but it
will  probably  be  inevitable  if Btk spraying continues as the
control method of choice for pest species. This problem  is  not
limited to the south coast. Large areas of the forests of BC are
sprayed annually with Btk to control native forest pests such as
spruce  budworm.  This  control of native pest caterpillars will
have the same effect on butterflies  and  moths  as  control  of
introduced pests such as Gypsy Moth. Rare species will be extir-
pated  throughout  much of the province over time, with only the
common species having the ability to recolonize an area  once  a
spray program is completed.

In  1984  researchers  isolated  the fungus Entomophaga maimaiga
from the Asian gypsy moth in Japan (Reardon &  Hajek  1993).  It
can  now  be  maintained in the laboratory by growing in culture
media rather than in caterpillars. Host range studies have shown
that not only does E. maimaiga not  infect  insects  other  than
Lepidoptera,  it  infects other Lepidoptera larvae at a very low
rate compared to Gypsy Moth  larvae  (especially  under  natural

Entomophaga  maimaiga  is apparently responsible for the decline
in gypsy moth outbreaks and damage over the last  few  years  in
eastern North America. Even in western North America E. maimaiga
could  play  a  significant role in the natural control of Gypsy
Moth, but more time is needed  to  determine  whether  it  would
result in constant lower populations of the Gypsy moth as it did
in  eastern  North  America. This raises the question: Should we
allow Gypsy Moth to become established in BC, rather  than  risk
extirpating  rare  species  of butterflies and moths through Btk
spraying, and then introduce biological control agents  such  as
E.  maimaiga  to  prevent  epidemic outbreaks? It is probably to
early in the research of E. maimaiga to know if it will success-
fully maintain  Gypsy  Moth  at  endemic  rather  than  epidemic
levels,  but  thought  (and  research  money) should be given to
consideration of the alternative strategy.

Literature cited:

Miller,  J.C.  1990.  Field  assessment  of  the  effects  of  a
   microbial  pest  control  agent on nontarget Lepidoptera. Am.
   Entomol. 36:135-139.
Miller, J.C. 1992. Effects of  microbial  insecticide,  Bacillus
   thuringiensis  kurstaki, on nontarget Lepidoptera in a spruce
   budworm-infested forest. J. Res. Lepid. 29: 267-276.
Otvos, I.S. and S. Vanderveen. 1993.  Environmental  report  and
   current  status  of Bacillus thuringiensis var. kurstaki. Use
   for control of forest and agricultural insect pests. Ministry
   of Forests, Victoria.
Reardon, R. and A. Hajek 1993.  Entomophaga  maimaiga  in  North
   America:  A  Review.  Appalachian Integrated Pest Management,
   USDA Forest Service, 22


The winner of the photo quiz in BEN  #  188  is  Alex  Buchanan,
Hobart,  Tasmania.  He  correctly identified two genera (Isoetes
and Erigeron) and he is close enough to be an antipode, although
hanging down slightly off the vertical position, if viewed  from

The second prize goes to Owen Wayne from Arkansas who recognized
Balsamorhiza  (not sagittata, though) and "perhaps Erigeron." He
wanted me to donate granola bars to some starving students:  "If
you dunk them in beer, they make a complete meal."

The  third  prize goes to Dave Clark, Victoria. Sorry, Dave, you
were too close to the source to beat  your  handicap.  You  were
right  with  Balsamorhiza  deltoidea,  Erigeron,  and Limnanthes

These were all the submissions I got.

Philip. A. Thomas, Hawaii, complained about the slow loading  of
the  contest  pictures. I worried about this, but since I am not
skilled in using the graphic  mode  (my  home  IBM  PC  has  the
original 1981 black-and-green screen and no graphic capability),
I was not able to fix it before the April 1 deadline.

These are the correct answers:

(1) Balsamorhiza deltoidea, (2) Isoetes nuttallii, (3) Lasthenia
maritima,  (4)  Sphaerocarpos  texanus  (liverwort),  (5) Jaumea
carnosa, (6) Erigeron salishii, (7) Limnanthes macounii.

Many thanks to all of you who visited  Victoria  freenet  Botany
web site (very much under construction).

Submissions, subscriptions, etc.:  aceska at victoria.tc.ca
BEN is archived at   http://www.ou.edu/cas/botany-micro/ben/

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