What are the holes in this scale insect?

[Africa]

I came across this large scale insect (which I presume dead) on my grape vine while trimming it. It called my attention the numerous tiny, evenly spaced holes on its surface. What is causing them? My guess would be emerging little ones from eggs laid by mother, or parasites?
I would be also interested in identifying the scale insect.

[Paul mabbott]

I've never seen anything like this so this is just speculation!
Most young emerge from the mother's remains at the sides - the dead 'shell' normally falls away in winter/spring. I'm not aware of any species in which the young gnaw their way out.
The scales are possibly infested by parasitoid wasp or fly - size is right but this is rather a large number and rather evenly spread.
An alternative is that the scale has been probed for food by an insect with a rostrum (most likely a true bug).
Fascinating observation . If no one here can help, I'd suggest that you send a picture to the RHS RHS Advisory Service / RHS Gardening

[Klaas Reißmann]

Hi,

the only explanation can be parasitoids, but I don't know to much about parasitoids in scale insects. I don't think this has got to do with emerging youngsters. But at least it is speculation, too.

Regards
Klaas

[Africa]

Thank you Klaas and Paul. Knowing a bit on the biology of these beasties does help to narrow it down. I will send the photo to the RHS.

[Dorts]

The biological control of scale insects in an enclosed environment is often done using parasites. Often different species of Wasp for different Scale insect.

I found this description of Metaphycus helvolus, a small parasitic Wasp used to control scale infestations in greenhouses.

"The adult female lays up to 6 eggs a day into soft scales. Before laying an egg, she tests the scale with her ovipositor (egg laying tube). In so doing she kills up to four times as many scales.

The larva develops inside the scale and eventually kills it. These parasitised scales appear darker and flatter than normal. The parasite pupates inside the scale body and the adult emerges by cutting a circular hole in the dead scale."
Defenders - Safe Effective Natural Biologist Pest Control for Gardeners

So that would seem to be the most likely cause of the holes.
Dorts.

[Paul mabbott]

Originally Posted by Dorts

The biological control of scale insects in an enclosed environment is often done using parasites. Often different species of Wasp for different Scale insect.
......Dorts.

Being a bit pedantic, but I think there's an important point here. These wasps and flies are not parasites but parasitoids - the name arose because their mode of operation, inserting eggs into or onto their host, is similar to the behaviour of many parasites.
The difference is that most true parasites do not kill their primary host whereas parasitoids always (=99.99% of the time) do.

Interesting reference.

[Africa]

Thank you Dorts for pointing out the website. It sounds like a likely explanation. I guess there must be many of this tiny fly species which are actually native and parasitise native scales (although I have no idea if this particular scale insect is native or not, having found it in a grapevine.
Thanks also to Paul for clarifying the difference between parasites and parasitoids.