Red Admiral hibernation

[Morten DD Hansen]

Hi all lepidopterists

I still have some comments on Red Admiral hibernation, which I do not consider hibernation, but only a temperature dependent inactivity.

Nick Bowles wrote:

>
> >Quite possibly many butterflies do move south in autumn.  There is very little evidence for that from the UK. Numbers certainly fall off from the north but few people have been able to point to actual southward movement in the same way that northern movement is een in hte spring.

In Denmark we see substantial movements of Red Admirals in fall, in some years more than 100.000 individuals have been counted at one single spot per day! From Finland there are reports (Jaakko Kullberg) of 50.000 caught in traps at one single island in autumn 1998.

> Many of the latest/earliest sightings here are of Red Admiral (V. atalanta) and Painted Lady (C. cardui).

Where are all the Peacocks and Small Tortoiseshells? They are far more common in winter. Why don't they fly when temperatures rise?

> However, there is evidence in the UK that the metabolic activity is lowered to such a state that it is certainly hard for me to see the difference.

If you subject well fed Peacocks and Red Admirals to the same conditions (constant temperature at 4 degrees C), Red Admirals die within 1 month, while Peacocks have a survival rate of  more than 90% after 180 days (Pullin 1987)! This might indeed indicate some difference in metabolic activity.


> Only one Painted Lady  has been 'proved' to survive from October in one year (1997) until April the following year (1998), though others are strongly suspected. (Some of our early sightings are probably migrants as those sen in several coastal areas on Jan 6-11 1999).

I think it's more probable that they have not had the time to leave England in autmun and hence have to overwinter. If the weather in autumn is poor, the lipid reserves of the butterflies are rapidly depleted (within 15-20 days). When the weather conditions better, the butterfly has to choose between migration or feeding. They feed.

> But there are many examples of well watched Red Admiral surviving similar lengths of winter.

I do not doubt that Red Admirals may survive the mildest winters in SW England, like they do in S Europe. But I do not think that their reproductive diapause involve hibernation.

> Larvae of Red Admiral have been found in virtually every stage of development and there is little doubt that some do manage to enter a diapause stage to pass the winter.

Diapause (which is neurohormonally mediated) has not been reported in larvae of Red Admirals, but they may survive low temperatures for a while.

> IN fact the most likely cause of the failure of over wintering larvae is the virtually disappearnace of stinging nettle food plants in hte frosts of winter.  In the few instances where they feed on Pellitory we expect that they fare better.

> So I would like to know what is the difference between lowering metabolic activity to the point where insects survive for months; and hibernation.  Is there really sufficient difference that the two conditions can be reliably distinguished?
>

I think the metabolic activity of Red Admirals is purely temperature dependent during the reproductive diapause! In winter, Red Admirals fly in North Africa and southernmost Europe, only because of higher temperatures. There may be a flight threshold (10 degrees C ???) in this species, but the behaviour (flying vs. inactivity) is not hormonally mediated.

>
> Conservation Officer  for  UTB\ Butterfly Conservation
> 94 Miswell Lane, Tring, Herts HP23 4EX   tel  01442 824 407

best wishes
Morten DD Hansen

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Morten DD Hansen, stud. scient.
Afdeling for Zoologi
Biologisk Institut
Bygning 135, Universitetsparken
8000 Århus C
tlf: 8942 2695
e-mail: biomddh at biology.au.dk
homepage: http://www.imf.au.dk/~dd/
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