Noctua pronuba

[AS]

Here’s some info on N. pronuba from Europe:

In Europe Noctua pronuba is *generally single-brooded* with
a dormancy period (aestivation) of the adults during
summer. The adults typically begin to emerge in May or
June, earlier in the south. (The earliest data from Morocco
are from March; see Rungs 1981). In central Europe we have
some April records in years with warm spring which we
attribute to single larvae that succeeded in developing
faster due to favourable microclimatic conditions. A first
peak of activity in June(/July) is followed by a period
with fewer records in July/August (depending on latitude
and elevation). A strong peak then follows from August to
September, the numbers declining toward October but with
some moths having been recorded well into November. The
overall situation is a bit more complex because Noctua
pronuba is also a well-known migrant that migrates both
within its range and beyond. (When you record small numbers
daily in your light-traps and suddenly hundreds appear in
one or two consecutive nights to dwindle to singletons in
the next nights, you can be certain that a migrating swarm
has been passing through.) Migrating N. pronuba moths –
single or in large numbers and often associated with other
migrants such as Agrotis ipsilon or Autographa gamma – are
regularly recorded in the Alps at elevations above 2.000 m
where N. pronuba is unable to develop (i.e. to hibernate)
(their direction seems to be south to north, mostly).

Experiments by Novak & Spitzer (1975), Cayrol (1972) and
others have shown that ovary development is determined by
photoperiod. In periods with long daylength (16-17 h;
spring and early summer) ovary development is delayed and
although the moths initially fly and feed they become
largely inactive afterwards. Short daylength (8 to 14 h;
late summer) triggers ovary development; mating and
oviposition occur after 3-4 weeks. It seems that climatic
factors play an additional role as there are indications
that ovary development is further delayed in the mountains.

If you keep caged moths you can easily observe their
reduced activity in the summer months. In Europe the
aestivation phenomenon seems to be strongest in continental
areas (eastern Europe) and less pronounced in atlantic
climate and in the north (where the flight period is
shorter anyway). There may also be individual differences.

Two further observations weigh against the two-generation
theory: There are no larval records (that I know of)
between June and August. And there are no egg-batch records
from the same period. From August to October, however, you
can easily find egg-batches in all typical locations.
Noctua pronuba prefers to oviposit on long stalks (dead
grasses, dry or withering long-stemmed plants etc.) which
are higher than the surrounding vegetation. Occasionally
other small cylindrical objects are used (e.g. wire-
fences). The eggs are tightly clustered around the stalk or
around the inflorescence of a grass or a small shrub. Less
often you can come across an egg-batch on a flat surface,
e.g. on the surface of a leaf. I once recorded the height
of 50 egg-batches: they were between 45 and 160 cm above
ground with the maximum number at around 70 cm – quite easy
to find. It’s very interesting to observe larval eclosion.
They emerge all together, feed on the eggshell and then
lower themselves to the ground on a thread. If it’s a windy
day – as often happens in autumn – they are immediately
carried up and away, trailing their thread, and thus the
several hundred larvae from an egg-batch disperse. The
total egg-load of a female is 2000 to 3000, in captivity up
to over 4000 (Cayrol 1972). So potentially the larvae might
be a problem in monocultures.

The very polyphagous larvae have been recorded from a
variety of plants from more than 20 families. Most of them
are herbaceous plants, grasses, shrubs, bushes and some
young trees. Generally Noctua pronuba is much less
a „climbing cutworm“ than N. comes and N. fimbriata. Larvae
of the latter are often seen 2-3 m high up in bushes or
small trees. Pronuba prefers to keep nearer to the ground.
There are some complaints that larvae have damaged garden
plants (mostly Brassica, Cichorium, Lactuca and the like),
but I don’t recall any serious cases in my area. You will
find detailed records in Cayrol (see below). The larvae can
hibernate in different instars. On 30 October 1989 I
counted the following on a 10 x 10 m square in a woodland
clearing: 1 L3, 4 L4, 3 L5 and 8 L6 (Lx being the larval
instar). In spring larvae can sometimes be found until as
late as the last June decade (all these data from south
Germany; Steiner 1998).

Here are some suggestions for further research in America:
1. Breed the species for more than 1 year to prove how many
generations per annum it has and observe the activity of
the adults (note: rearing the larvae is easy; it’s keeping
the moths relatively undamaged in cages for 4 months that
can be difficult).
2. Experiment with adults at various photoperiods and
observe ovary development and mating.
3. Carry out mark-recapture experiments to determine if
migration occurs and if possible in which direction (of
course adults disperse in all directions but there are
swarms that probably migrate in one direction).
4. Record larval hostplants (note: the egg-laying site is
not necessarily a hostplant). If the larvae should become
pests you will hear about it soon enough ...

Literature references follow:

Cayrol R A 1972. Noctuidae: pp. 1255-1520. In: Balachowski
A S (ed.): Entomologie appliquée à l’agriculture. Tome 2,
Lépidoptères. Deuxième volume. Paris (Masson) 1520 pp.

Novak I & Spitzer K 1975. Adult dormancy in some species of
the genus Noctua (Lepidoptera, Noctuidae) in Central
Europe. – Acta ent. bohemoslovaca, 72: 215-221.

Rezbanyai-Reser has published many papers on moth migration
in the Swiss Alps, most of them in the journal
Entomologische Berichte Luzern.

Rungs C C E 1981. Catalogue raisonnée des Lépidoptères du
Maroc. Inventaire faunistique et observations écologiques.
Tome 2. – Trav. Inst. scient. chérif., série zool. 40: 223-
588.

Steiner A 1998. Noctuinae: pp. 339-543. In: Ebert G (ed.):
Die Schmetterlinge Baden-Wuerttembergs. Vol 7. Stuttgart
(Ulmer Verlag). 582 pp.


Hope this helps you
Regards

Axel Steiner
State Museum of Natural History, Stuttgart, Germany


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