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BEN # 190
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@victoria.tc.ca Victoria, B.C.
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Dr. A. Ceska, P.O.Box 8546, Victoria, B.C. Canada V8W 3S2
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BOTANY BC - PEACE RIVER
From: SDELONG@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@mfor01.for.gov.bc.ca>
GYPSY MOTH & Btk: THREAT TO RARE LEPIDOPTERA (RE: BEN # 186)
From: Cris Guppy <cguppy@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-
lar.
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
conditions).
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
BEN PHOTO IDENTIFICATION QUIZ - THE WINNER IS:
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
Victoria.
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
macounii.
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).
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