| BEN |
| BOTANICAL ELECTRONIC NEWS |
|---|
| ISSN 1188-603X |
| No. 190 April 25, 1998 | aceska@victoria.tc.ca Victoria, B.C. |
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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
The pesticide which poses the most serious threat to the conservation of rare butterflies and moths is the otherwise environmentally 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 especially 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. israelensis 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 caterpillar.
When Btk is eaten by a caterpillar, the crystal protein and the spores damage the gut lining, leading to gut paralysis. Caterpillars stop eating, become limp and shrunken, die and decompose. 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 additional 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 Within a few days to a week the Btk is no longer active. 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 caterpillars, will be affected when Btk is sprayed. Garry oak ecosystems sprayed with Btk show significant reductions in both overall number of all butterfly and moth caterpillars (50% reduction) 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 populations, 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 recolonization 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 extirpated 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 successfully 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:
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:
Many thanks to all of you who visited Victoria freenet Botany web site (very much under construction).
Submissions, subscriptions, etc.: aceska@victoria.tc.ca.
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