Fróðskaparrit - 01.01.1999, Page 160

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NOTES ON TWO MIGRANT MOTHS FROM THE FAROE ISLANDS,
AGROTIS SEGETUM (L.) AND NOCTUA ORBONA (Hfn) (LEPIDOPTERA, NOCTUIDAE)
doptera. At the time when the moth was
recorded, SK had been collecting speci-
mens in the Faroes. During late June and
early July, the prevailing wind direction
from the northeast prevented any lepi-
doptera migrations from Central Europe,
cf. Table 1. On 2 July, the weather condi-
tions changed, and on the same day an evi-
dent migration of many Plutella xylostella
and a few Vanessa atalanta was observed
on the island of Sandoy, and on other is-
lands in the Faroes on the following days.
On 5 July, a great number of hill-topping
Red Admirals were spotted at 500 m a.s.l.
on Kunoy (Mr. Atli Vilhelm, personal in-
formation). Most probably, the specimen
of N. orbona was also transported during
the same period, suggesting that it had
reached northern Streymoy by 2 or 3 July.
In the neighbouring faunas, two speci-
mens were recorded in 1862 on Shetland
(Pennington, 1997). The authenticity of
these sightings has been questioned by re-
cent British authors (Bretherton et al.,
1983). In Scandinavia and Great Britain,
its distribution is comparable to Agrotis
segetum, and the moth is generally charac-
terised as local, thermophilic, and fluctuat-
ing in occurrence (Hoffmeyer, 1962; Nord-
strom et «/.,1969; Bretherton et al, 1983).
During recent decades, its frequency in
Denmark has been closely related to peri-
ods with warm summers, as 1964-1976, the
early 1980s, and most recently from 1994
onwards. In 1997, the species appeared
quite commonly in light traps in southem
and southeastem Denmark.
This pattem suggests that the local and
restricted populations of Noctua orbona in
northwestem Europe are reinforced during
warm summers by migration from the east-
em parts of Continental Europe. Due to its
status as a generally uncommon moth
species in Central and Westem Europe,
such stray specimens of N. orbona have not
earlier been recognised as migrants in Eu-
ropean literature. Such a pattern of disper-
sal may not be recognised until stray speci-
mens are recorded far away from their
breeding areas.
The early date of the Faroese record is
also of interest, as the ordinary period of
flight of the moth is in late summer from
late July to September, like its close relative
in the Faroes, Noctua pronuba. The middle
of June is the normal time for emergence of
both moth species. After a short flight pe-
riod, both sexes spend the main part of
summer aestivating in sheltered places un-
til they are sexually mature in early August
(Bretherton et al., 1983). The early date of
the Faroese record may suggest that an ear-
ly migratory potential is present in these
aestivating and teneral European noctuid
species. Such early migratory movements
are well known in other aestivating moth
species, such as the cosmopolitan Agrotis
ipsilon (Hfn.) and the Australian A. infusa
(Bsd.) (Williams, 1958), or the nearctic
Chorizagrotis auxiliaris Grote (Pruess and
Pruess, 1971).
Meteorological Factors Governing the
Transport of the Moths to the Faroes
The record of the two species in 1996 and
1997 was contemporaneous with a number
of long-range migrating lepidoptera that
regularly are observed in the Faroe Islands.