Purple hairstreak parasitism

[Padfield]

Every time I go past a suitable oak tree I now have a quick look for PH eggs, with quite a high hit rate!

Today I came across two with large holes bored into the side. They were on different trees but in the same area. I presume they've been parasitised - does anyone know what the parasite is?





I'm happy to say there are lots of perfectly healthy eggs too:



Guy

[Paul]

No idea about the parasite, but is it possible they've had a bit of warmth, hatched and burrowed into the bud?.... they look like the ones I've seen when the catty's upped and left!!

Oh, & I found some WLH ovae today in a new spot!! - looked for a hour then found 3 in 5 mins!!- will have to go back with camera

[Padfield]

I never thought of that, Paul. But I fear such premature emergence would be as lethal to the caterpillars as parasitism, as it will be some time yet before those buds are nutritious and edible. I will try and keep an eye on the healthy eggs at emergence time, though I may miss them as I'm off to India at the end of March, to visit my grandfather's grave.

I look forward to your WLH egg piccies!!

Guy

[Cotswold Cockney]

The 'prematurely' hatched little larvae may have bored their way deep into the buds, feeding within and protected from the elements. Some species definitely do this.

Monitoring WLH ova in the wild locally back in the 1970s saw empty ova in February, and cutttings of the Elms with flowers and buds placed in a jar of water showed minute frass droppings on the newspaper placed underneath the twigs. Later, as the became larger, they would emerge from the buds and flowers and rest on the twigs.

Same with Holly Blue raised on cuttings of Holly with empty egg shells.

When placing cuttings in jars of water, I cover the top of the jar with polythene/plastic secured by string. Punch tight holes in the plastic and insert the cuttings through those. This stops any adventurous larvae from the possibility of drowning.... A cold outhouse or unheated greenhouse is best for them as in the warmth indoors, they develope far too quickly and emerge out of season which is not good for their chances in the wild when released..
..

[Padfield]

Well that's very interesting! Up here (c. 1000m) trees are generally late in leaf, though I must admit they are often early in flower. Paul and CC have certainly made me think these might be empty eggs. If there's no chance of someone living inside (I wouldn't willingly destroy even a parasite), I might collect one of them (if I can find them again) and examine it under the microscope.

Thanks for the input.

Guy

[Padfield]

Another correspondent has told me that in his experience PH always emerges through the micropyle rather than throught the side, and thus that my eggs have indeed been parasitised. The correspondent has seen the phenomenon many times and speculates that a tiny wasp is the culprit. If I can, I'll try and dig out some more evidence!

Guy

[Pete Eeles]

Also - the buds are way too tight (I'd say) for a larva to bore into them. My experience is that they emerge as the buds are bursting, no doubt the buds and larva respond to the same trigger to synchronise their emergence.

Cheers,

- Pete

[Neil Hulme]

Hi Guy,
I think your 'correspondent' is correct on both counts. Hairstreak caterpillars will always emerge through the micropyle. This looks very much like the work of the tiny, parasitic wasp Trichogramma sp.
Neil

[Padfield]

Thank you, Kipper (and Pete).

Assuming it's a wasp, is the large hole an exit hole? If they're empty eggshells I'd be very interested in collecting them for closer examination.

In future years, when I'm not envisaging being out of the country at crucial times, I'll try CC's method of rearing PH on cuttings.

Guy

[Neil Hulme]

Hi Guy,
Yes, the newly emerged wasp will have chewed its way out of the egg through this hole. I think (not 100% sure) that the parent wasp will have inserted its egg through the micropyle - they really are tiny critters!
Neil

[Padfield]

Amazing. I shall try and recover one of these eggs when the latest snow has melted. It shouldn't be too long, as they're all laid on the sunny side of the trees.

Thanks again,

Guy

[Mikhail]

Guy, many hairstreak eggs are parasitised by Trichogramma wasps. They are the likely culprits.

Misha

[Cotswold Cockney]

Thank you, Kipper (and Pete).

Assuming it's a wasp, is the large hole an exit hole? If they're empty eggshells I'd be very interested in collecting them for closer examination.

In future years, when I'm not envisaging being out of the country at crucial times, I'll try CC's method of rearing PH on cuttings.

Guy

Oak cuttings do not do well in water for long ~ better in airtight plastic boxes ( not opaque to allow light ) and air the contents by opening the boxes at least twice a day ~ and check contents. Elm does better than oak and green Holly berries seem to do well when their cuttings are in water.

I must have raised a 100 PH ova over the years ~ never had a wasp emerge or one fail to hatch ~ mind you, that was back in the 1970-80s, maybe the situation has changed now in Gloucestershire..
.

[Paul]

Sorry, my part in this seems to have been a load of rubbish!!!
If you decide to hand rear some, make sure you do it in a way they emerge at the correct time of year for your area.... easy to have them emerging well early when they may be a bit lonely out there on release!

[Padfield]

Sorry, my part in this seems to have been a load of rubbish!!!

On the contrary - considering all the options is good, and I hadn't even thought of yours before you mentioned it!

My books say PH parasitism is relatively rare, but Tim Cowles went out yesterday and quickly found a parasitised egg (near Lyon) just like mine. Let's hope it's not a new trend.

The weather has turned grim again here, with temperatures not getting anywhere near zero and fresh snow on the branches. I'll probably stay indoors for a bit...

Guy

[Padfield]

Well, I collected an egg (the first one I showed above) and attempted to photograph it down the microscope. Hardly an unqualified success (depth of field a big problem), but here are some of the results:




(The micropyle seemed to be intact)







Guy