Crataegus monogyna, Dronten, two galled flowers in the inflorescence; © Arnold Grosscurt
opened gall with young pupa
Crataegus laevigata, monogyna.
That the species would live also on Pyrus, as Buhr writes, is not confirmed by Rheinheimer & Hassler.
Buhr (1964a), Lehmann & Hannover (2016a), Redfern & Shirley (2011a), Rheinheimer & Hassler (2010a), Roskam (2009a), Tomasi (2014a).