Canary Islands revisited

Thu Dec 20 05:05:13 EST 2001

The following quotes come out of an article (in the English language) by
Martin Wiemers (1995) in Linneana Belgica 15(2-3):63-84, 87-118. It is
highly recommended, the summary:

"This paper discusses the status and origin of the 32 butterfly species, a
third of which are endemics, known from the Canary Islands in the context of
the evolutionary history and the vegetation of the islands. On the basis of
personal investigations on most of the islands, records by several
colleagues and an evaluation of the extensive literature, an account of
habitats, early stages and larval food-plants is given and detailed
distribution maps are presented for the first time."

About Vanessa vulcania (Godart, 1819):

After the synonymy, it continues:

"Taxonomy and range

Macaronesian [= occurring on the Atlantic islands] endemic confined to
Madeira and the Canary Islands but closely related to the South-East Asian
Vanessa indica (Herbst, 1794) and sometimes considered as subspecies of the
latter. Leestmans (1978), in his revision of the genus Vanessa, discusses
the probable palaeoclimatic reasons for the vast gap in distribution between
vulcania and indica in detail and ranks vulcania as a separate species,
based upon differences in wing pattern and shape, as well as small
differences in [male] genitalia. Another paper on the probable origin of
vulcania without much new information and similar results has recently been
published by Shapiro (1992a). Unfortunately he was unaware of Leestmans'
publication (Shapiro 1992b). Single records of vulcania have also been made
in the Iberian Peninsula .... [snip] .... and also in East Germany [sic,
several dates, snipped], whereas a record from Britain (Turner 1982),
possibly an introduction by breeders, belongs to the related indica from
S.E. Asia."

The article continues with notes on Distribution, Habitat, Phenology, Early
Stages and Larval food-plants.
I was wrong - according to the article - in assuming that V. atalanta was
winning the competition. My own observations were only made during four
days; 3 vulcania against 5 atalanta. This was in a spot on La Palma where
the laurel forest (Tertiary relic) was disturbed (cut down and very young),
maybe the usage by humans is a decisive factor in the competition between
the two species.

About the introduction of Pararge aegeria on Madeira: both species seem to
use different niches:  "... (Shreeve & Smith, 1992). They found that the
recent colonizer, P. aegeria (which has not been recorded in the Canary
Islands), differs in habitat associations from the endemic P. xiphia. P.
aegeria predominantly established itself in disturbed, sunny sites including
pine and eucalyptus forests, where the endemic vegetation has recently
declined. Whether this decline is due to interspecific competition (which
interactions between adults did not indicate) or caused by anthropogenic
changes of surroundings is an unsolved matter."

Danaus chrysippus is (was) not a native of the Mediterranean : " in North
Africa as a migrant, [snip] which may at least become temporarily resident
[snip]. Tennent (1995) states that there is a strong evidence that the
species has established breeding colonies in Morocco, Algeria and Tunisia
within the last 50 years. In South Europe only migrants have been found, but
since 1979, when the first Spanish colony was reported from Almeria, the
species has spread along the Spanish coast up to Southern France and Corsica
[snip], reaching Sardinia [snip]."
(All 'snippings' here are literature quotes)

About the foodplants of D. plexippus:
"On Tenerife, larvae have most often been found on Asclepias curassavica and
on Gomphocarpus fruticosus, both members of the Asclepiadaceae. Cotton
(Gossipium arboreum), given as the foodplant by Rebel & Rogenhofer (1894),
clearly is of no importance nowadays. Owen & Smith (1989) discuss the choice
of food-plants utilized by the species on the Atlantic Islands. It is
remarkable that only alien Asclepiadaceae (from Central America and Africa)
and no native species, neither the widely distributed Periploca laevigata,
nor one of the endemic Ceropegia species, have been recorded as food-plants.
In greenhouse experiments by the same authors, six females bred from larvae
which were found on El Hierro (on Gomphocarpus fruticosus), also showed a
strong preference to lay their eggs on Asclepias species or Gomphocarpus
fruticosus. The africa derived Calotropis procera was also not found to be
exploited by Gran Canaria populations (van der Heyden 1992b)."
During the two weeks I spent on La Palma, I saw two D. chrysippus and one D.
plexippus. According to the article, both occur in higher numbers on
Teneriffa (habitat better suited ?).

The reason I said D. crysippus is a 'lesser evil' is the fact that it does
not compete with any of the species living in the Laurel Forests. These are
a Tertiary relic, (in the western Palaearctic) only occurring on the Canary
Islands and Madeira. Species typical for this habitat are V. vulcania,
Pieris cheiranthi, Pieris (?)brassicae wollastoni (Madeira - ?extinct,
?hybrid brassicaeXcheiranthi), Pararge xiphia/xiphioides, Gonepteryx
cleobule, G. (?)cleopatra maderensis, ...
If you go and visit the islands, spend some time in these forests, and
you'll understand why they are also known as the 'Islands of Eternal
Spring'. Don't wait too long, e.g. Gran Canaria has already lost 98-99% of
its original laurel forests.
But of course, if D. plexippus also uses Euphorbia spec., then it is a
direct competitor for Hyles tithymali tithymali Boisduval, 1832, another
Canary Islands endemic (though ?only subspecies).
Does D. plexippus thrive on Euphorbia? I've always thought that the
adaptation of the metabolism to a poison is a specialisation, making it
impossible for that species to use other foodplants that do not contain the
same poison. Or is the poison found in the Asclepiadaceae the same as or
related to the one found in the Euphorbia spec.?

Guy.

Guy Van de Poel
Guy_VdP at t-online.de

Royal Entomological Society of Antwerp
http://www.freeyellow.com/members/fransjanssens/index.html

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