Wednesday, August 22nd 2018
You may have seen these fascinating structures on wild roses of late; the Robin's Pincushion, is caused by the larvae of the Bedeguar Gall Wasp Diplolepis rosae.
This tiny little wasp will target an unopened bud (embryonic shoot) in which to lay up to 60 eggs using her ovipositor; this acts to alter normal cell development pathways leading to gall formation. The grub then develops inside the gall, and will emerge in the Spring unless tampered with.
Gall wasp grubs will often be predated by birds and small mammals, however there are other threats to the grub that occur within the gall itself.
A bedeguar can be home to a very complex community of insects, as the Bedeguar Gall Wasp grub may share its gall with inquilinus species' such as the grub of the Cynip Wasp Periclistus brandtii. Periclistus brandtii is unable to cause gall formation itself and depends entirely on the galls created by the Bedeguar Gall Wasp.
Unfortunately (for them) the grubs of both Diplolepis rosae and Periclistus brandtii are often parasitised by other insects whilst still within the gall, such as the Chalcid Wasps Eurytoma rosae and Glyphomerus stigma, and also the Ichneumon Orthopelma mediator.
If you've managed to keep up well done, however it doesn't end here! These parasitoids can themselves be parasitised by other insects referred to as hyperparasitoids (including the Chalcid Wasps chalcids Caenacis inflexa and Pteromalus bedeguaris).
On top of all of this insect parasitism the galls themselves are often attached by the parasitic fungus Phragmidium subcorticum.
In short these galls are incredible!
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