ze and shape of the galls are specific to the majority of gall wasps with about 70% of the known species living in various types of oak trees. Galls occur on nearly all parts of trees including leaves, buds, branches, and roots. Other species of plant where galls are commonly found include eucalyptus, rose or maple trees, as well as many herbs. Frequently, identification a of species of gall forming insect is easier by the shape of the galls produced rather than the insect itself. Some of the more common types of galls caused by the feeding of these insects are discussed below.
Oak artichoke galls develop as a chemically induced distortion of leaf axillary or terminal buds on Pedunculate Oak (Quercus robur) or Sessile Oak (Quercus petraea) trees, caused by the parthenogenetic gall wasp Andricus fecundatrix which lays single eggs within leaf buds using their ovipositor. The larva lives inside a smaller hard casing inside the artichoke and this is released in autumn.
Oak Artichoke Galls. Image Courtesy Rasbak
The galls of the rose gall wasp (Diplolepis rosae) are also distinctive and are known as bedeguars or robin's pincushions. These are found on the shoots of dog roses and have a length of up to five centimeters with red long-haired outgrowths. Inside the galls are several chambers, which may be occupied by larvae.
Robin’s Pincushion on Rose. Image Courtesy of Bjorn Appel
Knopper galls develop as a chemically induced distortion of growing acorns on Pedunculate Oak (Quercus robur (L.)) trees, caused by gall wasps which lay eggs within buds using their ovipositor. The gall thus produced can greatly reduce the fecundity of the oak host, making the gall a potentially more serious threat than those which develop upon leaves, buds, and stems. The large one inch gall growth appears as a mass of green to yellowish-green, ridged, and at first sticky plant tissue on the bud of the oak, that breaks out as the gall between the cup and the acorn. If only a few grubs are developing within, then it may appear only as a group o