Monarchs and Monoculture in southern Michigan

[Robert Dana]

Re Ken's question (below):
Approximately 18 million acres of Minnesota were prairie at the advent of European colonization/transformation. There were 11 Asclepias species in this prairie (A. syriaca, speciosa, ovalifolia, tuberosa, amplexicaulis, viridiflora, verticillata, lanuginosa, stenophylla, incarnata, and sullivantii). (There was also 1 forest species, A. exaltata). Not all of these occurred throughout the entire geographic extent of prairie in MN, and most of the species are associated with soil and moisture properties that limit their occurrence to more specific types of prairie (dry, sand, wet, etc.). But several species were widespread and common in the typical upland mesic prairie that dominated the 18 million acres. Milkweeds in these intact native prairie contexts rarely occur in the density that one sees in disturbed habitats (always A. syriaca), but basically every acre had some milkweed in it, constituting an enormous amount of biomass.   I have found D. plexippus larvae feeding on most of these 11 species, but I'm pretty sure that several, because of size, perhaps because of phytochemistry or other tissue properties, were not significant hosts. However, several of the most common species would have been, notably A. syriaca, ovalifolia, incarnata, probably speciosa. It would make a nice project for someone to try to develop an estimate of the milkweed resource of the midwestern prairie, along with a determination of the relative host-plant quality of the various species, and compare this with what is available now in the agricultural landscape that has replaced the prairie.

Robert



*************************************************************
Robert Dana, Ph.D.
MN DNR
Natural Heritage and Nongame Research Program
500 Lafayette Rd, Box 25
St. Paul, MN 55155
651 297-2367
Email: robert.dana at dnr.state.mn.us
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>>> Kenelm W Philip <fnkwp at uaf.edu> 8/27/05 5:03 AM >>>

snip

As to whether GM crops are harmful or harmless to butterflies (or to
other organisms--they are certainly as hard on weeds as they are
designed to be!)--that depends on the specific organism, and also
requires one to take a long view of the situation. Is the number of
milkweed plants in the midwest before the advent of GM crops larger
or smaller than the number before Europeans came to the New World? Is
the _current_ number larger or smaller? Are the masses of Monarchs in
the midwest an old event. or something of recent origin due to agri-
culture? I have no idea, but the Monarch researchers may know some-
thing about this.

snip

 But what I would like to see are data on the abundance of milkweed in the mid-
west through history. Is the pattern of weedkiller spraying in GM crops
allowing significant amounts of milkweed to survive? Is that amount,
whatever it may be, larger or smaller than the amount present before
the introduction of large-scale farming?

	Similar questions would arise for any butterfly foodplant in the
midwest.

		Ken Philip



 
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