Benson (1943) divided eight genera (Sirotremex was unknown to him) into two subfamilies, the Siricinae (Sirex, Siricosoma, Urocerus, Xoanon and Xeris) and the Tremicinae (Teredon, Eriotremex, and Tremex [Afrotremex was recognized as a rather special species but he kept it under Tremex]). Gauld and Mound (1982) proposed a formal phylogeny of the Siricidae based on the data provided by Benson (1943). As far as known, the larvae of Siricinae feed on conifers (gymnosperm) trees (hosts known for all genera except Sirotremex) and the larvae of Tremicinae are assumed to feed on flowering (angiosperm) trees (hosts known only for Eriotremex and Tremex). However, some larvae of E. formosanus have been reared from conifers in addition to flowering trees.
The Tremecinae as defined by Benson (1943) is a natural clade defined by four derived character states not seen in earlier symphytan superfamilies (see character states under “Notes on Affinities” under item 2b). The Siricinae as defined by Benson (1943) would have the ancestral state of the above characters. We propose a classification not too different from Benson’s. We still recognize the two extant subfamilies of Siricidae, but defined them differently. The Siricinae consists of the genera Sirex, Sirotremex, Urocerus and Xoanon. It does not include the genera Siricosoma and Xeris, which are transferred to Tremicinae. This way, both subfamilies are natural lineages defined by shared derived character states (see 1a and 1b above [under Notes on Affinities]).
A very unusual fossil, Megapterites mirabilis Cockerell, 1920, originally assigned to Pseudosiricidae (a junior synonym of Myrmiciidae) was illustrated by Maa (1949) and assigned by him to a new subfamily, Megapterinae, in the Siricidae. Rasnitsyn (1968) changed this classification by giving Megapterinae family status and then (Rasnitsyn 1969), based on the lack of forwing 2m-cu, moved Megapteridae to Myrmiciidae. Lutz (1986) moved M. mirabilis to the Formicidae and synonymized Megapterites under Formicium in the subfamily Formiciinae. Here we move M. mirabilis back to Siricidae for the following reasons.
The fossil consists of the apical 0.7 of a fore wing with the anal region missing (Fig. C1.45). Several features support our view that it is a sawfly of the family Siricidae. All studies of M. mirabilis agree that the wing is of a hymenopteran because the presence of a sclerotized stigma, and the pathways of veins M and CU are typical of Hymenoptera. Does M. mirabilis belong to Symphyta? Vein 1r-rs is widespread in Symphyta but does not occur in Apocrita. Is M. mirabilis a Siricidae? The very long cell 3R1 relative to 2R1, vein R1 at the apex of cell 3R1 far removed from the wing margin, the obvious petiole at the apex of cell 3R1, and cell M being much smaller than cell 2M are derived character states of Siricidae and support inclusion of M. mirabilis in Siricidae. The absence of vein 2m-cu, pointed out by Rasnitsyn (1968), may be a damaged section of the wing, as suggested by the marked divergence of veins M and CU and the lack of an anal region.
Megapterites mirabilis represents a distinct lineage with special ancestral character states not seen in other Siricidae. Vein Rs behind vein 1r-rs is aligned with vein 1m-cu (vein directed from midway along vein Rs+M to vein M in Siricinae and Tremicinae), and the veins at the apex of cell 3R1 are tubular (nebulous in Siricinae and Tremicinae). Both character states are common and widespread features of Symphyta. The very long cell 3R1 relative to cell 2R1 and the associated small cell 1M could be considered as shared derived character states of M. mirabilis relative to Siricinae and Tremicinae. Therefore, we agree with Maa (1949) that Megapteritinae is a subfamily of Siricidae and represents an earlier lineage relative to the Siricinae and the Tremicinae.
As defined here, the family Siricidae consists of three subfamilies: Megapteritinae, with one extinct species, Megapterites mirabilis Cockerell, 1920; Siricinae, with six genera [4 extant and two extinct genera, and the species, Urocerites spectabilis (Heer 1867) – according to Maa (1949), and Eoxeris klebsi (Brues 1926) – based on Maa’s description]; and Tremicinae, with 6 genera [all extant].
