Perhaps I should know this but............. Is there a ‘point of no return’ for a pupa whereby the adult has to emerge and expand its wings no matter what the prevailing weather conditions?
I live on the South Coast of Hampshire and like just about everywhere the weather has been unseasonal with pretty much 100% cloud cover and very cool temperatures almost continuously for about ten days.
I have a particular interest in the Duke of Burgundy at this time and regularly visit several local sites during the last week in April and most of May.
Normally by this time numbers have built to a point whereby I am seeing 20+ in a day at each site but I am currently [like most other people] seeing just ones and twos.
It got me thinking – have they had to emerge and are skulking in the undergrowth waiting for the sun/warmer weather to go about their business, or have they simply been able to delay emergence?
I realize that most larvae may have their metabolism slowed by adverse weather resulting in a longer period before emergence but does this effect pupa similarly especially! once the butterfly is fully formed?
Mark
The wonder of the world, the beauty and the power, the shapes of things, their colours lights and shades, these I saw. Look ye also while life lasts.
That's something I've been pondering too lately. I accept that once the imago has emerged there can be no mechanism in place to markedly delay the final phase (i.e. death), but earlier stages seem to be instinctively capable of elongating their life span, although by how much is the six million dollar question.
This is a very interesting point you have raised, and in short the answer is "yes, there is a 'point of no return' for pupae". Butterflies can certainly arrest the final stages of pupal maturation by several weeks beyond the usual term, consequent upon factors including, unsurprisingly, temperature. Also, the insect can possibly detect changes in atmospheric pressure while in the pupal state, which may explain why coordinated, en masse emergences often take place as anticyclonic conditions move in, following periods of low pressure/poor weather. However, research done on the White Admiral by Ernie Pollard in the 1970s indicates that the success rate of emergence from pupae (i.e. adult abundance) is reduced when this period is protracted; the extended period of susceptibility to predation is cited, although other agents are probably also influential.
The above factors may enable butterflies to 'hold back' during prolonged periods of poor weather (such as that we have suffered this spring), but then comes the 'point of no return'. For Duke of Burgundy, as for other species, the date for this will be influenced by local phenology; Hants Dukes always emerge a week earlier than in Sussex. For Sussex populations the 'point of no return' usually comes at c.10th/11th May, at which point many emerge irrespective of the weather. In 2010 I found the ground littered with Dukes on one site, but none could get airborne that day due to the cold.
In view of the many recent discussions about the effects of weather on spring butterflies, it is worth remembering 2010. Although less demoralising from a human perspective, the emergence of most spring species was significantly retarded, not by rain but by consistently low temperatures (particularly at night) as the result of relentless northerly and north-easterly winds. On 13th May they swung to the south-west, temperatures increased and on 14th May the butterflies emerged in spectacular numbers. Although some populations of some species will undoubtedly have been knocked back locally, the overall damage caused will not amount to a disaster so long as we start to see an improvement by this weekend. Fingers crossed.
Sussex Kipper wrote:
This is a very interesting point you have raised, and in short the answer is "yes, there is a 'point of no return' for pupae". Butterflies can certainly arrest the final stages of pupal maturation by several weeks beyond the usual term, consequent upon factors including, unsurprisingly, temperature. Also, the insect can possibly detect changes in atmospheric pressure while in the pupal state, which may explain why coordinated, en masse emergences often take place as anticyclonic conditions move in, following periods of low pressure/poor weather. However, research done on the White Admiral by Ernie Pollard in the 1970s indicates that the success rate of emergence from pupae (i.e. adult abundance) is reduced when this period is protracted; the extended period of susceptibility to predation is cited, although other agents are probably also influential.
The above factors may enable butterflies to 'hold back' during prolonged periods of poor weather (such as that we have suffered this spring), but then comes the 'point of no return'. For Duke of Burgundy, as for other species, the date for this will be influenced by local phenology; Hants Dukes always emerge a week earlier than in Sussex. For Sussex populations the 'point of no return' usually comes at c.10th/11th May, at which point many emerge irrespective of the weather. In 2010 I found the ground littered with Dukes on one site, but none could get airborne that day due to the cold.
In view of the many recent discussions about the effects of weather on spring butterflies, it is worth remembering 2010. Although less demoralising from a human perspective, the emergence of most spring species was significantly retarded, not by rain but by consistently low temperatures (particularly at night) as the result of relentless northerly and north-easterly winds. On 13th May they swung to the south-west, temperatures increased and on 14th May the butterflies emerged in spectacular numbers. Although some populations of some species will undoubtedly have been knocked back locally, the overall damage caused will not amount to a disaster so long as we start to see an improvement by this weekend. Fingers crossed.
Thanks for that considered and highly informative response, Neil. By coincidence, this weekend should see high pressure taking over from the series of low pressure systems that have swamped the UK for what seems like an eternity.
With any luck there may be another mass emergence during this period.
Thanks for your comprehensive reply Neil and it somewhat confirmed my suspicions. It is interesting to a note your comment on how different phenology effect the timing of Sussex and Hants Dukes. This would seem to suggest that the point of no return for Hants sites may have passed? However in my searching of two local sites I have spent some time searching suitable vegetation etc. to see if I could find any roosting adults - despite the weather - but to date for very little return. Certainly no littering of the ground The only ones I have encountered have been during the very brief spells of sunshine even if the temperature has been low.
Mark
The wonder of the world, the beauty and the power, the shapes of things, their colours lights and shades, these I saw. Look ye also while life lasts.
I was interested in your posts about delayed emergence, because I've been to the dunes at Ainsdale Southport looking for Common Blues. On Monday the day was cold but the sun in sheltered parts of the dunes was really warm, the Green Veined Whites were out in force, also the Small Whites, there was no signs at all of the Common Blue. Both the Duke and the CB have April as their emergence date so on reading your posts I'm hoping they may also be out this weekend. I plan to visit Gates Barrow to look for the Dukes this weekend all being well. Being in the North will this Make a differance to their emergence if delayed Anyone know Goldie
I have been checking out the Wall Brown pupa most days since finding it on the 20th April. Normally by now there would be several Wall on the wing in the area but to my knowledge only 3 have been seen so far. One of these was at the very beginning of April that is 3 weeks earlier than is normal here, due no doubt to the very warm March. In the Thomas/Lewington book it says that the Wall pupa stage is normally around 2 weeks. Without knowing how long the pupa had been there before being found this pupa is now well beyond that time. The top of the pupa has now changed colour to a pale yellow and the whole thing is not such a bright green now. After all this checking I just hope that all is still well with it and that warmer drier conditions will result in an emergence soon!!
In 1999 the Entomologist's Record and Journal of Variation included a paper entitled "Postponed emergence: a possible survival tactic in the Orange-tip butterfly" This reported that, with captive-reared stock, emergence from some pupae may be delayed by one or even two years. The contention is if this occurs in the wild, it may provide a safeguard against emergence in unsuitable conditions in a particular season. I believe the same author also reports on studies made on the Large Heath, where (in the far north of the country) it was found that a small proportion of larvae have a two-year life cycle and remain as third instar larvae throughout their second summer. This flexability is thought to enable them to cope with a more extreme climate and the unpredictable weather during the adult flight period.
I'm involved in a project to boost the numbers of Duke of Burgundy at Gait Barrows by captive rearing and release of stock from both Gait Barrows and a site in Cumbria (to increase genetic diversity) and my experience this year makes me sure there's a point of no return, and that the majority of my pupae reached it. They were colouring up, and appeared normal and healthy before we had weeks on end of dull, cold, wet weather. The pupae mainly just died, and the same seems to have happened with the wild ones, as there were very few Dukes at Gait Barrows this year. 2011 had been the best ever year there, with spread to nearly all the suitable parts of the reserve. Although some of the few that emerged were released at other parts of the site than the 'main Duke glade', there has been no signs of butterflies there other than the ones I released, no evidence of them breeding, and eggs have been deperately hard to find for rearing through for next year. Anything we'd achieved in breaking through the genetic bottleneck will be back to square 1, or worse, and it will take years to get back from this.
As someone who has put so much personal effort into conserving this species, I'm really saddened to hear this news. After such a good 2011 the Duke is going to take an almighty knock. The Sussex populations I care for have been 'down' by 50% - 75% on most sites, and that's after we were 'saved by the bell' with some good, late season weather. Elsewhere in the South, where emergence times are earlier than Sussex, I suspect there may be some bad news to come next spring, as some areas spent almost the entire flight season under cloud. However, the resilience of butterflies never ceases to amaze me, so as long as viable numbers emerge next year I think many sites will recover quite quickly. At least the food plant condition will be good!
Going back to the reference I made about Ernie Pollard's work on White Admiral (research done on the White Admiral by Ernie Pollard in the 1970s indicates that the success rate of emergence from pupae (i.e. adult abundance) is reduced when this period is protracted; the extended period of susceptibility to predation is cited, although other agents are probably also influential), I suspect desiccation plays a role in failed emergence from pupae.
I hope things don't look too grim for you next May.
I don't know Pollard's work on the white admiral,so can't comment. I think it could be unrealistic anyway to compare a species like the white admiral that overwinters as a larvae, to a Duke that has been in it's pupal case all winter. Duke's were on the wing 3 weeks early in 2011, so pupation was also brought forward, making it an even longer period as a pupa. Some of the later ones I had that did emerge, did so with crippled wings that weren't inflated - so I wonder if dehydration was a factor (not that there was any shortage of atmospheric moisture and the pupae were of course kept in as natural an environment as possible).
I searched again this evening and found only 2 plants with what might be larval feeding damage.
Edited to add - I think there must be more to it than dessication though. At the Cumbrian site where I do the transect, the drier areas had better emergence than the scrubbier, lusher parts (where only 1 butterfly was seen, and few eggs found subsequently). I know some of the pupae I had succumbed to fungal attack before February. Those that remained were moved onto fresh earth with a light coating of grit, and then re-covered with dry dead leaves. There's probably a combination of factors.
The only ones I have encountered have been during the very brief spells of sunshine even if the temperature has been low.
Anyone know 
