o .eg an Jo of En1tomol0lD' - Norsk entomologisk forening

Ematurga atomaria. Other species of Ericaceae,
Vaccinium myrtillus, V. vitis-idaea, Erica tetrafix
etc., also is important as foodplants for a high
number of the Macrolepidoptera inhabiting the
heath. Various grasses and sedges serve as foodplants
for many of the dominant Noctuidae,
like Cerapteryx graminis, Apamea monoglypha,
Amphipoea lucens and Celaena haworthii, while
several of the dominant Geometridae, like Thera
cognata, T. juniperata, Eupithecia pusillata and
E. intricata (Zetterstedt, 1839) feed on Juniperus.
Juniperus grows abundantly both in the
heath and on the grassland and the importance
of this plant as a food plant is reflected in the
high similarity between the Geometridae faunas
in the two habitats, shown by Renkonen's percentage
of similarity.
The bimodality in the total catch, with largest
catches in spring and late summer might be a result
of reduced efficiency of the traps during the
short and bright middsummer nights. Light
traps catch insects because the high illumination
ofthe traps relative to the surroundings interfers
with the normal photic orientation of the insects.
Anything that reduces the contrast will
have the effect of reducing the catch (Verheijen
1960). In Western Norway light traps must therefore
be expected to be more efficient during
the long dark nights in the spring and towards
the autumn than during the middsummer nights
(cf. Ulfstrand 1970, Southwood 1975). High
• background illumination might also have a direct
effect. Moonlight depresses flight activity in
insects (Williams 1936, Williams and Singh
195 I), and Persson (} 971) indicated that also the
normal night light in June might lower flight activity.
In any ease, in the open, flat terrain on
northern Sotra the background illumination in
• middsummer must be particularly noticeable.
The flight periods of the dominant species
show a high degree of overlap with the flight
periods recorded for the species elsewhere in
Southern Norway and in England (e.g. Bakke
1974, Williams 1939). Proceeding from south
towards north on the northern hemisphere the
flight periods of «vernal» species occur progressively
later with increasing latitude, and conversely
for the «autumnal» species (Wiltshire 1938,
1941 a,b). Hardwick (I 97 I) has shown that a
«phenological date» can be calculated for each
species, considering the lenght of the summer in
a given locality (actually the number of days
with a temperature above 42°F). When comparing
the time and duration of the flight periods
of the dominant species on northern Sotra with
their flight periods in other areas both the locality's
northernly possition and the effect of the
atlantic climate have to be taken into account.
An uneven sex-ratio is often experienced in
light trap catches and most often reflects differences
in trappability between the sexes due to
variation in phototactism and activity pattern.
For some species there also are differences in
flight potential between the sexes. The sex-ratio
obtained in light trap catches seems, however, to
be rather stable for many Noctuidae species.
Williams (I 939) recorded f. inst. 9 % females in
Xestia xanthographa, 11 % in C. graminis and
25 % in A. monoglypha. The corresponding sexratioes
in the light trap catches on northern Sotra
were 10%, 12 % and 28 %, respectively.
The tendency of the males to arrive a few
days earlier than the females, i.e. protandry, has
been experienced in light trap catches of different
insect groups (e.g. Svensson 1972). Wiklund
and Fagerstrom (I 977) suggested that protandry
is the optimal reproductive strategy of
males in species maintaining female monogamy,
or in species in which sperm from males mating
with virgin females on the average fertilizes a
larger number of eggs than sperm from males
mating with already mated females.
In areas where the heaths are burned regularly
Juniperus will disappear (Gimingham
1976), and the Macrolepidoptera community in
a well tended heath will accordingly contain fewer
species than recorded here for the heaths on
northern Sotra. However, the altered farming
habits in Western Norway have led to the spreading
of woody plants in the heaths, and a number
of herbs will in time undoubtedly invade the
heaths. As a greater variety of plants generally
leads to a greater variety of plant-eaters (Murdoch
et a1. 1972), a gradual higher diversity in
the Macrolepidoptera community in the heaths
is to be expected as an increasing number ofspecies
will find suitable foodplants. On the other
hand, if the attempts to vegetate the West Norwegian
lowland heaths with foreign conifers is
successful, the opposite trend will undoubtedly
be experienced.
ACKNOWLEDGEMENTS
I am greatly indebted to A. Fjeldsa for advise
and help during all stages of the study. My
thanks are also due to P. Andersen and W. Nielsen
for assistance during the fieldwork, to M.
Bravo for technical assistance and typewriting,
and to T. Solh0y for valuable comments on the
manuscript. Financial support was received
from the Norwegian Research Council for Science
and the Humanities (NAVF) and from
Norwegian Statoil.