Monday, September 14, 2015

Egg Lay Woes

Ably assisted by Mark Tutton (who seems to be better at finding iris larvae than me) I am two-thirds of the way through my annual monitoring of eggs and larvae in and around Savernake Forest.  

It is not good news.  Although I kicked off with a miraculous five larvae on the first tree I searched, the tally has since struggled to reach ten, suggesting that my final total may be a measly 15 - that's significantly lower than last year's count, which itself was the lowest recorded since monitoring began in 2009.  

Yesterday, in seven hours of combined searching Mark and I found a single 2nd instar larva and one failed breeding site (first instar feeding leaf & seat pad, + egg case base remnant, but no sign of the 'pillar).  

So far in Savernake, I am averaging one find per 3 hours searching. Brother Dennis, active in North Bucks, is doing much better, averaging one find per hour.  In 2009 and 2013 Savernake was produce a larva every 20 minutes.

There are several reasons.  In Savernake, the flight season kicked off late (mid-July), then the weather deteriorated and the females had to contend with windy and at times wet weather.  Iris hates wind.  I was not expecting a big emergence there anyway, due to a poor egg lay in 2014.  Also, most of the favoured sallows at the southern end of the forest have been rendered unsuitable this year by extensive damage by tree hopper nymphs, several breeding sallows have been badly damaged by squirrels, and others have been pruned back or removed during ride-widening work.   

This monitoring is, of course, based on the assumption that the butterfly lays the same proportion of its eggs low down annually - reachable from the ground with a shepherd's crook.  There is no evidence to support or counter that assumption...

For the record, the few larvae that are around are changing from 2nd to 3rd instar now.  

The prospects for the 2016 flight season are, at this distance, not great...

Here's yesterday's 2nd instar larva - 

And here's His Tuttonship, at the joyous moment of finding his first iris larva - 

Mark is now on 2 not out...

I am on 997 not out (accrued during a marathon innings of 40 years), but I'm not particularly confident about reaching the magical four figures this year...

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