Population crash of N. antiopa in DK

[Runar Krogen]

Hello

Here where I live outside Trondheim, Norway, I have experienced a kind of
population crash of Aglais urticae. The reason for this is a parasite
(wasp). In order to carry out a project on mark and recapture of this
species, I collected several hundred caterpillars during July. Early in
this process I collected young, mostly second instar larvae. These
developed into butterfies. But later in July I collected several full grown
larvae. Almost all of these became wasps. I have seen these wasps
everywhere here around in July and August, often flying around nettles
(Urtica dioica). Since I am not familiar with these parasites, I do not
know the name of the species. When I compare the thousands of caterpillars
I have seen here where I live earlier this summer to the very low number of
adults in August and September, I am sure that Aglais urticae has suffered
dramatically from this wasp.

On the other hand, Polygonia c-album, which normally is much rarer than
A.urticae, has been rather common here from mid August and until the last
days. Besides, I have collected several larvae of Vanessa atalanta in
August and September, and none of these have been attacked by the wasp. V.
atalanta does also use nettles.

Concerning Nymphalis antiopa, I observed 3 overwintering specimens early
this season here around Trondheim, but have seen no one during late summer
and autumn. I must mention that the species is a migrant to this part of
Norway. This summer I have not visited the region of Norway where it is a
permanent breeder and can therefore not give any information on the general
status of the species at the moment. But most probably the species has
suffered from the cold summer and will be low in number. After the cold
summer of 1987 the species became scarce for a few years, but was rather
common again in 1992 and has been so until 1998 in south central Norway. 

Concerning the two migrants, Vanessa atalanta and V. cardui, I have seen
only very few fresh adults of the new generation. One V. atalanta was
observed to day. On the other hand I still find caterpillars and pupaes
here around. They are very delayed, and some have died because of cold
weather. I have found deep-frozen cardui-larvae in localities exposed to
frost. Most probably more or less all vanessa larvae and pupae will die
during October, eventually November, and not develope into butterflies. It
is simply to late here now. 

Runar Krogen, 
Trondheim, Norway
rkrogen at online.no