Monday, September 26, 2022

Larval Search Update

I am still more than struggling to find Emperor larvae this autumn, finding one for every 2 hours 30 mins of actual leaf searching - that's as bad a find rate as after a cold, wet summer. This is in the S Glos / N Wilts / SW Oxon region which was not drought affected and where very few sallows dropped leaves. Sallow foliage conditions there are Very Good.

I am also finding precious little else: hardly any of the moth larvae I normally find at this time of year (e.g. Buff Tip, Clouded Border, Pale Tussock, Pebble Prominent, Swallow Prominent). Yesterday, at last, I found the first batch of larvae of the sallow foliage-feeding sawflies normally encountered whilst searching sallows in autumn (this one is probably the common sallow-feeder Euura pavida) - 

It seems that the egg lay was very low, at least low down. I am concentrating on searching in the shadiest places, where all the larvae I have found have been located. 

One theory is that the egg lay was not poor, but that there was a high failure rate of baby L1 larvae - as can happen in heatwaves (I first noted this in 1976), coupled with hatched egg cases falling off the leaves. 

Such losses leave no tell-tale signs, whereas the vacant seat pad and old feeding leaves of predated L2 larvae are quite prominent (and have been diligently recorded by me each autumn).

This is tricky. I have no experience of eggs (hatched or unhatched) coming unstuck, but of the paltry nine larvae I have found so far this autumn the egg case base was present in only three instances - that's unusually low and may suggest that eggs (hatched or unhatched) might have come adrift in the hot weather.  

The show continues - I need a bigger sample, and I should eventually make some sense of the situation. It's not critical (at least away from the drought-struck South East, where it might be) but it is deeply concerning, and is totally outside my experience. As Fred Trueman used to bemoan on Test Match Special, usually when England were leaking runs through an untenanted third man boundary: "I don't know what's going off out there anymore!"

I have yet to find any sign of Emperor larvae or eggs in Hailey Wood, Cirencester Park Woods - my local wood, where I followed and chronicled the likes of 'Boris', 'Jacob', 'Rishi', 'Priti' etc. earlier this year. Nothing, and I'm keeping a keen eye open for egg case bases and vacant leaves from failed L2 larvae.

The results of my annual stratified random sampling for PE larvae in Savernake Forest will be particularly interesting. I've carried this out there each autumn since 2009.

No comments: