monarchs:Australia and North America

[John Lane]

When monarch butterflies reached Australia (aided by humans), they found numerous native
Asclepiadaceae, upon which they could become established. Although monarchs may prefer
introduced milkweeds, native genera include: Leichardtia, Ischnostemma, Pentatropis,
Cynanchum, Secamone, Hoya, Gymnanthera, and Cryptostegia (all known hosts of native Australian
Danaines). Source: Common & Waterhouse's Butterflies of Australia.

If you want exact dates for first reported occurrences, the original work on the spread of
monarchs with reference to islands in the Pacific and Australia was Samuel Scudder (and L. H.
Gulick). See: Psyche (1875) 3:263-275 and Scudder's Butterflies of the Eastern United States
and Canada with special reference to New England (1888-1889) under the monarch entry.

I would add to Paul Cherubini's comments one potentially interesting difference in monarch
overwintering biology between California and Mexico, on the one hand, and Australia (Sydney,
at least) on the other.  In North America, overwintering monarchs
are reported to all be in reproductive diapause.  But at Sydney, it is my understanding that
(at some locations, at least) where monarchs overwinter, and hostplants grow adjacent, part of
the population is reproductively active, with oviposition and immatures present through the
"winter" period.

At Santa Cruz, CA, there is a milkweed garden maintained adjacent to the very large
overwintering monarch colony at Natural Bridges Beach State Park, and reproduction clearly
ceases each fall: oviposition falls drastically to zero and latest-season immatures suffer
greatly increased mortality. (Milkweeds are not native to this part of California.  Whether it
is a great idea to maintain this garden here is a separate issue, but one perhaps other
monarch biologists might wish to take up with State Parks ecologists).

Can any southern California workers document reproduction through the winter season anywhere
close to overwintering aggregations?


John Lane
15954 Wolf Mtn. Rd.
Grass Valley, CA. 95949
johnlane at nccn.net



Paul Cherubini wrote:

> John Grehan wrote:
>
> > It was my understanding that the monarch was already in NZ and Australia
> > before human introduction of the host-plant, but that they were not able
> > to permanently establish in the absence of the hostplant. I also understand
> > that there is no migration phenomenon like that in America - is that correct?
>
> A monarch biogeographer, Richard Vane-Wright has studied the situation in detail and
> found the monarch became established in Hawaii and many other central and south
> Pacific islands is the mid-late 1800's. This timing coincides with the advent of fast
> moving steam powered trading ships. It is interesting to note that the areas in Australia
> where the weedy swan plant became established are the same areas where the native
> eucalyptus forests were clear cut to accomodate agricultural interests.
>
> The seasonal migration/overwintering phenomenon in Australia is just like that in America
> except the numbers of butterflies involved and the distances they travel are smaller. Right
> now is late autumn in the Sydney area and hundreds of monarchs can be found clustering
> in at least a dozen eucalyptus groves slightly west (inland) of the city. Clustering also
> occurs in New Zealand at this time of the year, but the migration there has no been
> studied in detail.
>
> Paul Cherubini, Placerville, California
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