Holly Blue
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Dave McCormick
- Posts: 2388
- Joined: Fri Mar 16, 2007 8:46 pm
- Location: Co Down, Northern Ireland
- Contact:
Holly Blue
I have searched where I live and have only seen one holly blue this whole year. Anyone know why this could be and has anyone else seen this? Last year I counted loads of holly blues, well 16 in one small area in 5 mins of being in area, this year, I have found none in area. All the areas I found HB's in last year have not changed and I don't know whats up, kinda miss seeing them as I was the first to discover them wher I live.
Cheers all,
My Website: My new website: http://daveslepidoptera.com/ - Last Update: 11/10/2011
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My Website: My new website: http://daveslepidoptera.com/ - Last Update: 11/10/2011
My Nature videos: http://www.youtube.com/user/DynamixWarePro
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Neil Hulme
- Posts: 3595
- Joined: Fri Feb 08, 2008 8:27 pm
Re: Holly Blue
Hi Dave,
Holly Blue numbers are in almost constant inequilibrium with a 'host-specific', parasitic ichneumon wasp Listrodomus nycthemerus. If Holly Blue numbers build up, through a period when the wasp is at a 'low ebb', then L. nycthemerus will start multiplying rapidly, as opportunities to parasitise the butterfly larvae increase. As the wasp numbers increase the balance is tipped in its favour, and the Holly Blue numbers will 'crash'. This constant battle for supremacy results in a see-sawing in the abundance of both the butterfly and the wasp. We had lots of HBs in 2008, causing a major increase in the parasitic wasp, resulting in the spectacular drop in butterfly numbers in 2009. The 'cycle' will now start again, as the wasp numbers will drop back, with a decrease in the number of potential 'victims'.
Neil
Holly Blue numbers are in almost constant inequilibrium with a 'host-specific', parasitic ichneumon wasp Listrodomus nycthemerus. If Holly Blue numbers build up, through a period when the wasp is at a 'low ebb', then L. nycthemerus will start multiplying rapidly, as opportunities to parasitise the butterfly larvae increase. As the wasp numbers increase the balance is tipped in its favour, and the Holly Blue numbers will 'crash'. This constant battle for supremacy results in a see-sawing in the abundance of both the butterfly and the wasp. We had lots of HBs in 2008, causing a major increase in the parasitic wasp, resulting in the spectacular drop in butterfly numbers in 2009. The 'cycle' will now start again, as the wasp numbers will drop back, with a decrease in the number of potential 'victims'.
Neil
Re: Holly Blue
Hi Dave, this was asked before, here's what I wrote then...
The relationship between the Holly Blue and the ichneumon wasp Listrodomus nycthemerus is well documented and a natural cycle exists where each species ebbs and flows in population density according to that of the other.
When Holly Blue numbers reach a certain density the ichneumon wasp can really thrive, populations of this hymenopteran soar, until ultimately the Holly Blues numbers are adversely affected by a disproportionate number of these parasites. The result is a population crash which in turn impacts the nycthemerus numbers in subsequent years, resulting (it is considered) in the near (or actual) extinction of the parasite in certain areas. This then allows a natural boom in Holly Blue numbers as they are left to breed relatively free from this attractive little predator. Ultimately of course the Holly Blue numbers again reach a stage where nycthemerus can once again redistribute itself and begin to increase it's own population densities.
At some point during this cycle a point of relative harmony must be reached where both parasite and host coexist without the numbers of either one impacting the other adversely.
Holly Blue numbers have increased rapidly in recent years and one thing is fairly certain - nycthemerus will not be far behind....
The old "eggs laid in spring are on Holly, summer eggs are laid on Ivy" belief has been proven to be a little too much of a generalisation. While Holly Blues will use different larval food plants according to the generation to ensure that the young larvae have the tenderest flowers and developing seed so beneficial to their early development, Holly Blue will lay on a whole variety of food plants. Dog Wood is especially favoured by the spring brood, even it would seem in areas where there is plenty of Holly available.
Similarly a lone, large Holly will support a small colony all year round, with the summer brood larvae developing successfully on the young berries just as the spring brood larvae fed on the flowers and tiny developing fruits a few months earlier.
Felix.
The relationship between the Holly Blue and the ichneumon wasp Listrodomus nycthemerus is well documented and a natural cycle exists where each species ebbs and flows in population density according to that of the other.
When Holly Blue numbers reach a certain density the ichneumon wasp can really thrive, populations of this hymenopteran soar, until ultimately the Holly Blues numbers are adversely affected by a disproportionate number of these parasites. The result is a population crash which in turn impacts the nycthemerus numbers in subsequent years, resulting (it is considered) in the near (or actual) extinction of the parasite in certain areas. This then allows a natural boom in Holly Blue numbers as they are left to breed relatively free from this attractive little predator. Ultimately of course the Holly Blue numbers again reach a stage where nycthemerus can once again redistribute itself and begin to increase it's own population densities.
At some point during this cycle a point of relative harmony must be reached where both parasite and host coexist without the numbers of either one impacting the other adversely.
Holly Blue numbers have increased rapidly in recent years and one thing is fairly certain - nycthemerus will not be far behind....
The old "eggs laid in spring are on Holly, summer eggs are laid on Ivy" belief has been proven to be a little too much of a generalisation. While Holly Blues will use different larval food plants according to the generation to ensure that the young larvae have the tenderest flowers and developing seed so beneficial to their early development, Holly Blue will lay on a whole variety of food plants. Dog Wood is especially favoured by the spring brood, even it would seem in areas where there is plenty of Holly available.
Similarly a lone, large Holly will support a small colony all year round, with the summer brood larvae developing successfully on the young berries just as the spring brood larvae fed on the flowers and tiny developing fruits a few months earlier.
Felix.
Re: Holly Blue
One of those crashes has probably occurred in my locality too. I only saw three or four during the whole first brood period, with brief glimpses of just two at my local patch where I was regularly seeing them last year.
Re: Holly Blue
Same story in my neck of the woods Eccles.
Has anyone else noticed a lack of Holly Blue this year? it would be interesting to know if this lull in sightings is across the board...
Felix.
Has anyone else noticed a lack of Holly Blue this year? it would be interesting to know if this lull in sightings is across the board...
Felix.
Re: Holly Blue
Two so far this year, including a very worn individual last week.
Re: Holly Blue
I was just thinking this myself as my local Cemetery is a good site for Holly Blue; whilst I have seen a few at the right times (including some more this week) their numbers are nowhere near where they were 2 years ago, when it was possible to see several in the space of a few minutes at peak periods.
A good example of parasite/host cycles in action, I guess.
N
A good example of parasite/host cycles in action, I guess.
N
"Conservation starts in small places, close to home..."
Re: Holly Blue
I saw a couple of holly blues in the spring and only a couple since so numbers well down here too.
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Cotswold Cockney
- Posts: 487
- Joined: Sun Dec 31, 2006 9:39 pm
- Location: GLOUCESTERSHIRE
Re: Holly Blue
Not as many through my garden this spring and summer but still more common than in an average Holly Blue year.
This butterfly does indeed use a wide variety of larval foodplants. Visiting another butterfly enthusiast who lives on the other side of Gloucester back in the early 1980s, whilst chatting in his extensive garden, we observed a female Holly Blue laying on the tender young shoots of a Virginia Creeper growing profusely over a barn on the property. I have this creeper growing over the south and west facing wall of my double garage. I occsionally check those tender terminal growth buds but not spotted a single ovum on the plant in four years of checking. Less than a metre away from the wall is a mature female Holly Bush. I found larvae on that this year and previous ones.
Where I work there is an extensive and dense Holly Hedge regularly trimmed about a metre high. After some years it is now a dense barrier and many of the bushes are female. Walking along that hedge during my lunch breaks on sunny days, in both late April and early June this year I saw several females laying on the flowers over that period.
I have observed this attractive little butterfly in the climax Beech Woodlands on much of the Cotswold Hills near where I live since the 1970s. Mature Hollies are frequent and widespread in the Beech woods. Some years both male and female Holly bushes have a paucity of flowers and thus, few if any berries on the female bushes for the larvae to feed on. I suspect that in additiion to parasites affecting numbers, flower and berry density plays a large part in the wide fluctuations of this butterfly's populations. Plants and trees have good and bad years too.
In good flower and berry years, I can find dozens of ova on the Hollies in the Beech Woods quickly and easily. In springs where flowers and berries are scarce, it's a struggle to locate one or two ova and these are laid near the tender young leaves as there are no flowers. I have followed up observations on these ova laid near leaves. I have never found a feeding larva on subsequent follow up checks. Larvae are easy to locate on later checks of Hollies with plenty of green berries growing from the earlier flowers.
I have observed Holly Blue females checking Dogwood in the same woods but, never seen one actually lay. They also spend time checking a mature Mahonia in my garden ~ again never seen one lay on it. The berries the Mahonia produces later are avidly eaten by the Blackbirds that frequent my garden ....
..
This butterfly does indeed use a wide variety of larval foodplants. Visiting another butterfly enthusiast who lives on the other side of Gloucester back in the early 1980s, whilst chatting in his extensive garden, we observed a female Holly Blue laying on the tender young shoots of a Virginia Creeper growing profusely over a barn on the property. I have this creeper growing over the south and west facing wall of my double garage. I occsionally check those tender terminal growth buds but not spotted a single ovum on the plant in four years of checking. Less than a metre away from the wall is a mature female Holly Bush. I found larvae on that this year and previous ones.
Where I work there is an extensive and dense Holly Hedge regularly trimmed about a metre high. After some years it is now a dense barrier and many of the bushes are female. Walking along that hedge during my lunch breaks on sunny days, in both late April and early June this year I saw several females laying on the flowers over that period.
I have observed this attractive little butterfly in the climax Beech Woodlands on much of the Cotswold Hills near where I live since the 1970s. Mature Hollies are frequent and widespread in the Beech woods. Some years both male and female Holly bushes have a paucity of flowers and thus, few if any berries on the female bushes for the larvae to feed on. I suspect that in additiion to parasites affecting numbers, flower and berry density plays a large part in the wide fluctuations of this butterfly's populations. Plants and trees have good and bad years too.
In good flower and berry years, I can find dozens of ova on the Hollies in the Beech Woods quickly and easily. In springs where flowers and berries are scarce, it's a struggle to locate one or two ova and these are laid near the tender young leaves as there are no flowers. I have followed up observations on these ova laid near leaves. I have never found a feeding larva on subsequent follow up checks. Larvae are easy to locate on later checks of Hollies with plenty of green berries growing from the earlier flowers.
I have observed Holly Blue females checking Dogwood in the same woods but, never seen one actually lay. They also spend time checking a mature Mahonia in my garden ~ again never seen one lay on it. The berries the Mahonia produces later are avidly eaten by the Blackbirds that frequent my garden ....
..
Cotswold Cockney is the name
All aspects of Natural History is my game.
All aspects of Natural History is my game.
Re: Holly Blue
I watched one laying on dogwood last year at Denbies.
Re: Holly Blue
One second brood (?) seen on laurel in my firm's garden at work yesterday. Normally the earliest butterfly I see on the Isle of Wight in March/April.