Alexeter Förster, 1869

Chen, Hsuan-Pu, Huang, Chia-Lung & Shiao, Shiuh-Feng, 2025, A taxonomic revision of the genus Alexeter Förster (Hymenoptera, Ichneumonidae, Ctenopelmatinae, Mesoleiini) from Taiwan, with descriptions of six new species, ZooKeys 1250, pp. 315-358 : 315-358

Genus Alexeter Förster, 1869

Alexeter Förster, 1869: 212. Type species: Mesoleptus ruficornis Gravenhorst, 1829. Designated by Viereck 1914: 7.

Adranes Förster, 1869: 205. Type species: Tryphon multicolor Gravenhorst, 1829. Designation by Townes et al. 1965: 255. Synonymized by Townes et al. 1965: 255. Preoccupied by Adranes Leconte, 1850.

Zemiophron Förster, 1869: 206. Type species: Mesoleius laevissimus Strobl, 1903. Designation by Perkins 1962: 464. Synonymized by Perkins 1962: 464.

Diagnosis.

According to Townes (1970), Gauld (1997), and Wharton (2015), this genus can be distinguished from other genera of Mesoleiini by the combination of the following characters: sculpture of head and mesosoma generally matt, granulate or minutely coriaceous; mandibular teeth usually equal in length (lower tooth longer in few Holarctic species and all known Neotropical species); notaulus usually distinct at least near anterior margin of mesoscutum; fore wing areolet usually present; fore wing 1 cu-a usually opposite to M & RS; T 1 long and slender, usually longer than 2.5 × its posterior width; T 1 with latero-median carinae absent, dorsal lateral carina distinct, and glymma always distinct; lateromedian longitudinal carinae of propodeum distinct posteriorly and forming an area petiolaris with median part of posterior transverse carinae.

This genus is similar to Barytarbes , as some Alexeter species share the absence of anterior and median portions of the lateromedian longitudinal carinae on the propodeum and have mandibles with the lower tooth longer than the upper. However, Barytarbes typically features a shorter and broader T 1 and a propodeum with weaker lateromedian longitudinal carinae in the posterior part. Additionally, some Barytarbes species lack a glymma on the T 1, distinguishing them from Alexeter .

Townes (1970) also mentioned that some Alexeter species are challenging to separate from genera such as Campodorus , Lagarotis , and Alcochera . Generally, Alexeter can be separated from Campodorus by having a clypeus with sharp, truncate or rounded ventral margin, flat in lateral view or with subventral transverse ridge or median elevation (clypeus strongly bulging medially and subapically with bilobed ventral margin in Campodorus ), and areolet usually present (always absent in Campodorus ). It can also be separated from Lagarotis in having mesopleuron granulate or minutely coriaceous (heavily sculptured, e. g., minutely rugose, in Lagarotis ). Lastly, it can be separated from Alcochera by the mandible with teeth usually equal in length (lower tooth always longer than upper tooth in Alcochera ), and notaulus distinct at least near anterior margin (weak in Alcochera ).

Remarks.

In this study, we employed two criteria to determine the generic placement of the Taiwanese mesoleiines: morphological characters closely aligned with the generic definition proposed by Townes (1970) and the notes on Wharton’s website (summarized in the Diagnosis above); and when applicable, specimens with COI sequences similar to those identified as Alexeter in online databases such as BOLD Systems and GenBank.

The characters distinguishing this genus from morphologically similar genera – such as the length of the mandibular teeth, the length and strength of the notauli on the mesoscutum, the presence of a fore wing areolet, the propodeal carinae, and the length of metasomal T 1 – exhibit considerable variation. Therefore, the generic boundary of Alexeter and other mesoleiine genera is ambiguous, challenging the generic position of some species ( Townes 1970; Wharton 2015). The vague generic boundaries may indicate that the currently defined Alexeter is non-monophyletic, which is preliminarily supported by the COI - based phylogeny reconstructed in this study (Fig. 2 ). It suggests the necessity of a more comprehensive taxonomic revision of Alexeter and similar genera.

Figures

Figure 2. Maximum-likelihood phylogenetic tree of the species of Alexeter Förster, 1869 and its morphologically similar genera based on the COI dataset (809 bp; HKY + F + I + G 4 in 1–809 \ 3 and 2–809 \ 3, TIM 3 + F + G 4 in 3-809 \ 3), with species delimitation results and clades of Alexeter labeled on the right side of the tree. Taxon name in bold indicated the new species described herein. Branch lengths of the tree are proportional to the inferred number of nucleotide substitutions per site except for the root Ctenopelma nigrum. Circles on the nodes indicate different SH-aLRT / UFBoot values. Nodal support with an SH-aLRT value of < 80 % and a UFBoot value of < 95 % is not shown. Abbreviations: SH-aLRT, SH-like approximate likelihood ratio test; UFBoot, ultrafast bootstrap approximation; XOR, one or the other but not both; M, male; F, female.