Tenthredinidae

Diversity

The ± 900 European species of this family have strongly divergent habits. Many species just live freely on the plants. However, most mining sawflies also belong to the Tenthredinidae (in particular the subfamily Heterarthrinae).

Galls

The genus Salix consists of a large number of species. Mainly the mountains and boreal regions of the northern hemisphere are particularly rich. Most species can be separated with difficulty, also because they readily hybridise, especially where the natural distribution patterns have been disrupted by human activities. This is the typical picture of species swarm at the start of its evolution. Despite the seemingly shallow differences between the different Salix species, the species of the Pontania complex show a surprisingly close association with individual willow species. Also in the Pontania complex the differences between the species are minute, sometimes even just statistical: this also is a swarm of young species. The evolution of the Pontania swarm is superimposed on that of the Salix swarm!

Mines

Tenthredinidae mines are medium-sized to large blotch mines without in initial corridor. In principle they are upper-surface, but the layer of parenchyma that is left at the floor of the mine is so thin -and also dries out quickly- that the mines appear full-depth.

Traditionally much emphasis is put on the oviposition site (near the leaf margin or in the centre of the leaf) and whether the frass in concentrated in the first part of the mine. The last character is not really reliable. If a larva still is present, this enables a much more secure identification.

Interestingly, all species lie on their back in the mine (with exception of Pseudodineura, a Ranunculus miner).

The many non-mining Tenthredinidae are fairly polyphagous, but contrariwise the leafmining species are extremely strict monophagous. Most species hibernate as pupa.

The larvae of the mining species are strongly adapted to their way of life, among other things in the more or less strong reduction of the thoracic feet and prolegs, and the extreme flattening of the head that has become chisel-shaped, with the mouthparts projecting anteriorly. They all belong to the subfamily Heterarthrinae. There is one exception, viz. the genus Pseudodineura, just mentioned. This is much less well adapted, with a globular head and mouthparts working downwards; this genus belongs in the subfamily Nematinae.

larvae

Within the Tenthredinidae the mining larvae are characterised by a strongly, almost chisel-like, head, except in Endophytus and Pseudodineura, two genera that stand apart in the family, and do not seem to be yet fully adapted to the mining way of life. Another character is that the sternites of at least the thorax, but often also one or more abdominal segments, bear a dark spot.

key to the larvae of the mining genera