Andricus fecundator

A. fecundator has a life cycle with encompasses a sexual generation as well as an agamic (all female with no need to mate) generation which cause different galls in different locations of the common oak trees Quercus robur and Q. petreae.

The sexual generation was previously named A. pilosus before it was realized to be two generations of the same species. The hairy catkin gall is the sexual generation gall and can be found from May to June on oak catkins. It measures about 2x1.5mm in size. It is pointed and covered in long, dense, white hairs. The surface is not ridged and the catkin is usually not distorted. It contains a single cell and the gall matures towards the end of may. The wasp pupates in the gall usually on the tree, and emerges from the end of may through to august.

The female measures 1.4-1.8mm
Its head is shiney black and lightly sculptured with mid sized, very dark brown eyes and translucent yellow ocelli. The antennae have dark brown scapes with darker bases and the other 13 or 14 segments are gold, darkening to the tip.
The thorax is black and semi glossy, with light sculpture in parts and afew hairs towards the back. The tegulae are black and the wings clear with heavy, mid brown veins and short brown hairs. The legs consist of a dark brown femora and the rest is dark yellow.
The gaster (abdomen) is segmented and blocky but not compressed sideways. Its colour is black with dark chestnut at the rear and extreme front. It is semi glossy and slight sculpture and has a longish testaceous ovipositor sheath.

The male measures 1.3-1.8mm
The head is black and heavily reticulated with large black eyes and chestnut ocelli. The antennae consist of 14 segments and the flagellum are mid brown, as is the pedicel but the scape is dark brown.
The thorax is black with black brown tegulae. The wings are clear with dark neutral brown veins and short dark brown coarse hairs, although they can be sometimes paler. The legs consist of dark brown coxae and femora tapering to dirty yellow pale joints.
The gaster is slender pointed and tiny with a single main segment, glossy dark brown in colour with few large hairs at the front.

There is one recorded hyperparasite associated with this gall, Mesoplobus xanthocerus.

The artichoke gall is caused by the agamic generation. It is common and found on the terminal and axillery buds of oak trees from june to september. The gall is in appearance similar to an artichoke or hop. It is pointed (though not always and can be football shaped) and covered with bud scales and varies tremendously in size from 20x12mm to 30x20mm. Its colour is green, although after maturity at the end of july this changes to a light brown.

The outer scales of the gall conceals a large cavity, inside which is a small inner gall which is occupied by a single wasp. This small inner gall drops out of the exterior covering at maturity, leaving the empty artichoke part of the gall remaining on the trees for several years sometimes. After the inner gall has fallen to the ground the larva inside then pupates, emerging the following spring in march to april. Longer periods of waiting emerge have been recorded on many occasions and may sometimes take 2-3 years.

The agamic wasp has a large variation in size and measures 2.2-4.8mm with an average of 3.5mm.
The head is black, lightly sculptured, with dark hairs. The eyes are small and mid brown and the ocelli are dark. The antennae are dark brown to black and covered with short hairs. There are 14 segments.
The shiney black thorax is very hairy and lightly sculptured. The tegulae are chestnut and the wings are clear with pale brown veins and hairs. The legs are hairy and dark brown, getting slightly paler lower down.
The gaster (abdomen) is bright chestnut with diagonal darker stripes from half way down, semi translucent.

One inquiline, Synergus crassicornis, and several hyperparasites of this gall include, Aulogymnus trilineatus, Eupelmus urozonus, Megastigmus dorsalis, Torymus auratus (=nitens).

More detailed descriptions and identification keys are available from Robin Williams at the British Plant Gall Society.

top of page