Symphyta

Sawflies

The two blades of the ovipositor, which is a common character of all Hymenoptera, are modified here into two saw blades, which are used by the female to cut a wound in a plant’s issue and deposit an egg. Often the plant reacts by the formation of callus, an “oviposition scar”. In the cecidological literature they often are discussed as “protocecidia”. Often eggs are deposited on a row on a petiole of midrib, in two rows at either side of the midrib, or in the very lead margin.

Aproceros leucopoda © Hans Jonkman: ovipositing female

on the very leaf margin.

The larvae are strictly phytophagous. They strongly resemble the caterpillars of Lepidoptera. Free living sawfly larva generally are quickly recognised by having between their head and thorax a distinct “neck”: in true caterpillars the head always is retracted more or less deeply into the thorax. When disturbed may sawfly larve take a characteristic position: erect, with the in an S-curve. Because sawfly larvae tend to be communal this is quite conspicuous and often photographed.

The similarity between caterpillars and sawfly larvae partly resided in the common possession of prolegs. Sawfly larvae have a pair of prolegs at least on the second abdomen segment: true caterpillars never have prolegs on that segment. The most common proleg arrangement in sawflies is on segments 2-8, and 10, i.e. eight pairs, while true caterpillars never have more than five pairs. The prolegs of sawfly larvae don’t bear crochets at their end, while these are seldomly missing in true caterpillars. However, in mining larvae of both Lepidoptera and sawflies both legs and prolegs may be more or less reduced, so this differential character cannot always be applied.

Sawfly larvae have one stemma (ocellus) at either side of the head, true caterpillars almost always have a group of sex stemmata there (Chevin, 1998a; Stehr, 1987a).

The final larval stage of Symphyta may be quite different from the previous: feet and mouth parts are reduced; this so-called prepupa is colourless and not or hardly mobile. At this stage the larva does not feed any more.

references

Blank, Schmidt & Taeger (2006a), Blank, Taeger, Liston ao (2009a), Gauld & Bolton (1988a), Liston (1995b), van Ooststroom (1976a), Taeger & Blank (1998a).