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Andricus curvator, like many gall wasps, has 2 generations per cycle. One being sexual and the other being agamic (all female who can lay fertile eggs without the need to mate). Each of these two generations creates a different gall on the host tree which is oak Quercus spp..
The sexual generations gall is known as the Curved leaf gall, and is common on oaks from May to July onwards, on the leaf or sometimes in the twig. On the leaf it can be described as a globular swelling, of about 8mm across, that distorts the leaf and midrib. Sometimes several galls may coalesce. The twig galls form a swelling in the twig about 13x9mm across which courses bending of the twig. Each gall has 2 cells, a thin walled cavity with an inner gall containing a single wasp larva. The wasp pupates in the gall whilst on the tree. The gall matures in July and the wasp will then emerge from July through August.
The female wasp is 1.9-2.8mm in length and has a black shiny head with large dark eyes with the antennae being pale chestnut but darkening after the first few segments. 14 segments in total.
The thorax is glossy black with dark brown tegulae. The legs having black coxae and and the rest being yellow brown with browning in the middle of the tibia and femur. The wings have neutral brown wings and hairs.
The gaster (abdomen) is fat, deep and segmented. Black and glossy with some paler tinges on the edges of the segments.
The male wasp is 2-2.3mm in length. The head is gloosy black with sparse pale hairs. The eyes are large and very dark brown. The antennae are yellow chestnut, darkening after the first few segments, with a dark scape, fifteen segments in total.
The thorax is black and glossy with dark brown tegulae. The legs are dirty brown yellow with darker tinged patches in the centre of the tibia and femur, and darker coxae. The wings are clear with strong brown to paler viens and medium brown hairs.
The gaster is segmented, though not obviuosly. Smaller than the females, it is glossy black with a short chestnut petiole.
Inquilines found in the curved leaf gall as as follows; Synergus albipes, S. crassicornis, S. galaepomiformis, and S. nervosus
Hyperparasites of this gall are; Aulogymnus arsames, A. pallarum, A. gallarum f. pulchra, Eupelmus urozonus, Eurytoma brunniventris, Megastigmus dorsalis, Mesopolobus albitarsus, M. amaenus, M. fasciiventris, M. fuscipes, M. sericeus, M. tibialis, Torymus flavipes, T. geranii and T. notatus
The agamic generation was previously named A. collaris before it was realized to be two generations of the same species. The agamic generations gall, known as Collard bud gall, measures about 3x2mm and is found on terminal and lateral buds of oak trees, and occasionally on Artichoke gall (Andricus fecundator)scales from August to September. The gall is well hidden until maturity, which is at the end of September, and shows the tip only which is brown in colour, often encircled by a pale ring. It contains a single cell and the wasp pupates in the gall on the ground, emerging March to April of the following year.
The agamic wasp is about 2.8mm in length. Its head is small, dark brown to black and moderately hairy. The eyes are small, dark brown in colour and the ocelli are small and pale. The antennae are chestnut coloured with 14 segments.
The thorax is glossy with very dark brown/black to paler black striped. the tegulae is pale chestnut. The legs are pale chestnut with darkened coxae. The wings are clear with pale neutral viens and hairs.
The diamond shaped gaster is segmented, deep chesthut with dark markings.
The gall is often invaded by 2 inquilines; Synergus albipes and S. nervosus, and a hyperparasite; Mesopolobus amaeneus.
More detailed descriptions and identification keys are available from Robin Williams at the British Plant Gall Society.
