Wednesday, 18 January 2017

Still Fixated by Knopper Galls

Yes, I haven't moved on (partly because there is not much else of note under the unrelenting grey skies, but then the galls continue to surprise).  In the last few days many more insects have emerged from the knopper galls that I collected from under a common oak (Quercus robur) in the third week of December, and subsequently kept in a closed container at a steady 20℃.  From the 14 galls of different shapes and sizes so far  there have been   6 of the alien host gall wasp Andricus quercuscalicis.    These are from the agamic, that is, non-sexual generation, and are therefore all female.

But far more numerous,- more than 60 - other insects have emerged.   All look very similar and I am reasonably certain that they are almost all parasitoid wasps with perhaps one or two of iniquiline wasps among them.  Parasitoids attack the host wasps that create the gall in the first place, whereas iniquiline wasps simply take up home in the gall - uninvited lodgers that can alter the shape of the developing gall.

It does make for a puzzle.   A paper from 1991 by Hails and Crawley (J. Animal Ecology 60 (2) 545 - 61) found little parasitism in the non-sexual generation i.e the galls on common oaks, unlike in France where there was much more activity by parasitoid wasps.  A more recent paper  however by  K Schonrogge et al ( Insect Conservation and Diversity, 5 (4). 298-311) lists 14 parasitoid wasps and 5 iniquiline wasps associated with knopper galls, all as far as I am aware UK natives.   Knoppers are a recent introduction so maybe over time native parasitoid wasps are adapting to the alien.

I counted 55 of the emerging wasps and grouped them on size and appearance.   My summary for which there are photos below was:

Type A 3.5 mm long    29  (metallic sheen)
Type B 2 mm long       22  (very similar to type A, but smaller)
Type C 2 mm long         2  (metallic green with bright yellow legs)
Type D  3.5 mm long     1  (all black)
Type E  2 mm long         1  (almost all black)

Attractive little beasts and as my wife tidily summed it up "lost to the world, no-one sees them".

Here is the gallery with some attempt at identification, or more precisely speculation.

Type A (maybe Mesapolobus amaenus or M. tibialis)


Type B (very similar to Type A, but smaller maybe a different sex (?), Mesapolobus amaenus or M. tibialis perhaps)


Type C (maybe Mesapolobus sericeus)

Type D ( maybe Eurytoma brunniventris)


Type E (perhaps the only iniquiline,  maybe Synergus sp.)


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