Fróðskaparrit - 01.01.2009, Side 125

PLANTUVØLIR OG VØLAMÍCCJ (DIPTERA: CECIDOMYIIDAE) íFØROYUM
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Discussion
As is to be expected, the species richness of
plant galls and gall midges in the Faroe Is-
lands is very poor in comparison with
species richness in continental parts of Eu-
rope. In the Faroe Islands we found during
one week only ten gall-causing and gall-as-
sociated organisms occurringon seven host
plant species. It is the lowest species number
that we found during one-week investiga-
tions in any part of Europe. Usually during
such a period we have found about 50-60
species of gall midges, as is indicated in the
followingexamples.
In the island Sjælland (Denmark) we
found at individual localities from 5 to 43 gall
midge species (Skuhravá et ai, 2006). The
richest species composition including 43
species was found during a one-day excur-
sion at Store Dyrehave near Hillerød, 42
species at Tisvilde and 39 species at Farum.
The average species number per locality de-
termined from all records of Sjælland is 22. It
is relatively high and it approaches the aver-
age species number of the Czech Republic
situated in Central Europe, which is 26
(Skuhravá, 1994a, 1994b). In the Hautes-
Alpes in south-eastern France at altitudes
from 850 to 2645 m a.s.l. we found during
one week 107 gall midge species and the av-
erage species number was 25 (Skuhravá and
Skuhravy, 2004). In the surroundings of
Trondheim in middle Norway we found 56
gall midge species during one week and in
Harstad on the island of Hinnoya in northern
Norway, far beyond the Arctic Circle, even
35 species of gall midges (Skuhravá and
Skuhravy, in preparation).
During one week in south-eastern
Britain we found 60 gall midge species which
were associated with 45 difFerent host plant
species belonging to 25 plant families
(Skuhravá and Skuhravy, 2007). The average
species number per locality was 14.
The gall midge fauna of the British Isles
includes 620 species of the family Ce-
cidomyiidae and may be considered as very
rich (Chandler, 1998). It is the result of ex-
tensive investigations of many research
workers that studied gall midges and their
galls mainly during the 20th century. It is nec-
essary to stress the importance of the found-
ing of the British Plant Gall Society and its
journal Cecidology in 1985 and the contribu-
tion of its members to the development of
knowledge about gall insects in Britain. Nev-
ertheless, the British Isles are explored
relatively unevenly. Many plant galls and gall-
inducing organisms are known mainly from
the southern parts, from England and Wales,
and relatively little is known about the plant
galls of Scotland and of islands situated in
the north of Scotland. Investigations
directed to plant galls were done only in
Orkney Islands and nothing is known about
galls of Hebrides and Shetland Islands. From
Orkney Islands 28 gall-inducing organisms
are known, of them 16 gall-causing animals
and 12 gall-causing fungal organisms
(Spooner,1986a,b; Redfern, 2002). Orkney,
the archipelago of 70 islands, is situated 16
km off northern Scotland. The flora is much
more species rich than that of the Faroe
Islands and trees and shrubs occur in Orkney,
although in low numbers. Most of the
islands are farmed for hay and sheep.
The absence of native trees and shrubs
in the Faroe Islands is the main reason for the
low number of gall inducing organisms. Trees
and shrubs in Europe are the most frequent