NORSK ENTOMOLOGISK TIDSSKRIFT - Norsk entomologisk forening

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Ill-I, Table V, and perhaps Samples 11-1,
Table IV).
Stickel (194S) and Shelford (1954) relate
similar experiences from rivers in the D.S.A.
On islands previously submerged for two
months, the latter author found a rather rich
insect fauna. among others a Carabid beetle
which had clearly spent the period in the
river. The assertion of Lehmann (1965) that
Carabid beetles should not be able to survive
for 14 days on an island submerged by water
most probably is correct only if the island
lacked trees and bushes.
During inundations the imagines of fossorial
beetles (Clivilla fossor, Dyschirius spp., Bledius
spp., Psammodius asper, and Aegialia sabuleti)
are partly forced out of their burrows and
accumulate in the manner described above
(Sample Ill-I, Table V). However, in silty
substratum some individuals of these species
are able to survive, buried in the submerged
earth, even for quite long periods (Samples
IV, Table VII).
The experiments indicate that a greater
proportion of Psammodius asper than Bledius
spp. stays buried during inundations, but all
the specimens remaining in the substratum
were dead after a submergence of seven days
at IS-20°C. Submerged beetles have a longer
survival time at low temperatures than at high
(Palmen 1945, Hurka 1956), but ability for
long survival submerged in the river is hardly
attributable to low temperatures alone, as the
experiments showed that Bledius spp. mostly
live only a short time in cold water. Larvae
of Melololltha hippocastalli F. lived longer in
soil than in sand or water alone, but about
the same time in sand and water alone
(Hurka 1956). If there is little current, sites
with compact silty ground with a surface layer
mixed with humus covered with some vegetation,
as in Samples IV (Table VII), seem to
remain intact during floods, and burrows
probably retain air. In spots of obviously
similar type, several Bledius species could
survive submerged for weeks (Larsen 1936).
As no compact humus-mixed surface layer
THE EFFECT OF INUNDAnON 129
existed in the experiment with Psammodius
asper and Bledius IOllgulus, the air was clearly
forced out of the burrows, and the beetles
were consequently killed. If currents exist in
flooded areas and the substratum is coarser,
the fossorial species (incl. Bembidioll argenteolum,
B. lappollicum. and B. velox) are
forced out of their burrows (as indicated by
experiments) or, if not, most of them are
probably killed.
Even in years with exceptionally long flood
periods, a new generation of Coleoptera is able
to develop. Thus immature specimens of,
among others, Bembidioll lit orale, B. petrosum.
B. semipullctatum, B. femoratum. B. bruxellellSe,
and Tachyusa leucopus were found in
August 1965; the size of the population of
Bembidioll schueppeli in June 1966 was rather
high and immature beetles of B. IUllatum were
taken during and after the flood until mid­
July.
It is likely that the new generation of the
imaginal hibernators of Bembidioll spp. in
1965 partly originated from eggs deposited
after the inundations. The period between the
draining of the spots and the finding of
immature beetles was nearly two months, a
period probably sufficiently long to produce
a new generation. Many females had not
deposited all their eggs before the flood, since
the egg-laying period for most species is from
May to late June or July (Andersen in prep.).
Experiments reveal that females of beetles at
low. in contrast to high, water temperatures
do not deposit eggs, even when constantly
submerged, and, as long as the females are
alive, the eggs probably remain undamaged.
As a distributional factor, transport along the
river by the spring floods cannot, contrary to
the opinion of Wiren (1954), be regarded as
unimportant, compared with transport later in
summer.
Some Carabidae and Staphylinidae larvae,
mostly those staying on the surface when the
sites are flooded, together with larvae having
a dense pubescence, e.g. Cantharidae larvae,
survive by being washed up (Sample Ill-I,