Spring 2012 newsletter - Butterfly Conservation

The Trials of a White-letter Hairstreak Douglas Goddard
The White-letter Hairstreak had a
good season in 2011. Observers sent
in records of larvae found on Wych
Elm in Daventry and Boughton,
the adults were seen from 10th June
until 28th July, and several new sites
were discovered, notably Wicksteed
Park.
In Fermyn Wood, there are a
number of elm trees, some of which
provide sightings of White-letters
reliably each year. One lies at a ride intersection
in Cherry Lap, and here, at the beginning of July,
pupae were to be found under the leaves and good
numbers of the adults were emerging and laying
eggs. Commas also use the tree as a foodplant and
their larvae were also easy to find here.
The dark pupa
While searching and photographing Comma
larvae on 4th July, a White-letter pupa was still to
be seen, long after the emergence of others. Dark
brown in colour, it had clearly been parasitized
and was not going to hatch. I decided to take it
home to note further developments. A
week later, sure enough, a small wasp
emerged from the pupa, sawing off
the end to make its exit. I photographed
the specimen and sent it to Mark Shaw at
Edinburgh. He identified it as a female of
Virgichneumon tergenus (right), a known,
6
but rarely collected, parasitoid
of the White-letter. It attacks the
host in the pupal or prepupal state,
so is only found in pupae. It has
been reared from Black Hairstreak
(Perkins’ Royal Entomological
Society Handbook), and the
National Museum of Scotland has
specimens from Silver-studded
Blue, Common Blue, satyrium
esculi (from Spain) and three from
White-letter Hairstreak, including
mine. The hibernating strategy of this wasp is
not known; if it, presumably, over-winters as an
adult, only the female will do this, having mated
beforehand.
On 1st October, Andy Wyldes and I visited the wood
again, looking (unsuccessfully!) for Purple Emperor
larvae. As we walked through Cherry lap, the work
of the Forestry Commission was much in evidence,
the lower branches of sallows and other trees having
been hacked away by mechanical cutters to make the
route clear for lorry access. Our favourite elm had
not been spared this destruction, several of the lower
branches lying in a heap on the ground. We searched
the branches and found a couple of eggs and cleared
the remaining ones into a heap to look through
later. That evening I took a few of them home and
searched them, discovering eight more eggs. Closer
inspection revealed that three of these had exit holes
made by another parasitoid, a tiny wasp. The rest
will be kept and hopefully reared in the spring to
be released as adults, along with any others we find
among the remaining branches later on.
Predation of butterflies in their early stages is
widespread, and these discoveries serve to remind
us that it can be extensive in some years. Of a
hundred eggs laid by a female butterfly, only
two must survive to adulthood, to replace the
original pair which mated and keep the
population level stable, so normally species