Posted by John Bratton on 08-03-2012 16:53
#1
I was reading a book review yesterday. The book is called Wild Hares and Hummingbirds, and the reviewer said one thing he'd learned from it is that "our small tortoiseshell butterfly population is being significantly reduced by a parasitic fly which has recently appeared in Britain". Does anyone know the full story, please? I'm guessing it is a tachinid.
It wasn't a very glowing review of the book overall.
John Bratton
Posted by ChrisR on 08-03-2012 19:25
#4
I just had a look at that link - it's the first time I have read it. I quote:
The primary reason for this decline is due to the expanding range of a tachinid parasitoid fly called Sturmia bella which was first recorded in Britain in 1999.
Crikey, I hardly know where to start :D Sadly, the page just repeats the same rumours that were put about by the media years ago when the story first broke. For a start
Sturmia was first recorded in the UK in 1998 (many years after Small Tortoishell populations started their decline) and was reared from a Peacock butterfly in Hampshire. If you look at Owen Lewis's research it shows that populations of Small Tortoishell have actually risen in some places where
Sturmia is found, while areas where
Sturmia has not been found (in the far north) have experienced terrible declines.
It is without doubt that any parasitoid will have *some* effect on their hosts but it is absolute fantasy to say that the decline in Small Tortoishell is primarily due to
Sturmia bella. Parasitoids that wipe out their hosts are very rare indeed! ;)
My own personal theory is that the Small Tortoishell has been in decline for quite some time (at least the early 1990s) and we can probably blame this on man's unsympathetic use of the countryside and to the effects of climate change, although it is going to be very hard to point the finger at anything specific.
Sturmia is quite common where it occurs but it is unlikely to a major factor in the decline because it occurs across the entire palearctic region and doesn't seem to cause much of a problem there.
:)
Posted by John Bratton on 09-03-2012 17:08
#6
Thanks for the links. I'll look out for it on Anglesey.
Newspapers seizing on a juicy theory rather than studying all the facts? I can't remember that ever happening before.
John Bratton