Cretolixon, Lohrmann & Zhang & Michalik & Blaschke & Müller & Jeanneau, 2020

Lohrmann, Volker, Zhang, Qi, Michalik, Peter, Blaschke, Jeremy, Müller, Patrick & Jeanneau, Laurent, 2020, † Cretolixon - a remarkable new genus of rhopalosomatid wasps (Hymenoptera: Vespoidea: Rhopalosomatidae) from chemically tested, mid-Cretaceous Burmese (Kachin) amber supports the monophyly of Rhopalosomatinae, Fossil Record 23 (2), pp. 215-236 : 227-228

Cretolixon – a common ancestor of Rhopalosomatinae and Olixoninae?

As it would “undoubtedly” render the Rhopalosomatinae paraphyletic, Krogmann et al. (2009) argued against Engel’s subfamily classification, thus ignoring earlier morphological studies supporting a sister group relationship between the macropterous rhopalosomatids and the brachypterous Olixon , i.e., Brothers and Carpenter (1993), Brothers (1999), and Guidotti (1999). Brothers and Carpenter (1993) and Brothers (1999), based on their phylogenetic analyses, list nine potential synapomorphies for the Rhopalosomatinae. However, since most of these characters are not applicable to the morphologically aberrant Olixon it remains unclear whether these character states are novelties for the subfamily or whether they have evolved in the stem of the family with a secondary loss or derivation in the Olixoninae. The same might be true for the 22 characters received by Guidotti (1999) in her analysis of the generic relationships of rhopalosomatid wasps.

One of Guidotti’s potential apomorphies for the Rhopalosomatinae is a stiff apical bristle on the second labial palpomere ( Fig. 9e, f ). Olixon has a similar structure on the third maxillary palpomere ( Fig. 9d ) that has also been interpreted as a novelty for the genus by Guidotti (1999). The discovery of both apical bristles, i.e., one each on the second labial and the third maxillary palpomere ( Fig. 8b, c ), in Cretolixon alatum , leads to the conclusion that both bristles were already present in the common ancestor of both groups. Thus, it is the reduction of one or the other of these bristles that adds to the morphological evidence for the monophyly of each subfamily, respectively. The innovation itself likely occurred earlier in the common ancestor ( Fig. 10 ).

Krogmann et al. (2009) postulated that the single long bristle on the apex of the first flagellomeres of some Olixon species ( Fig. 3d ) is homologous to one of those two apical bristles present in the recent macropterous genera ( Fig. 3a ). For the first flagellomere, however, this line of arguments needs a slight modification. The single long bristle on the apex of flagellomere I of some Olixon species is most likely homologous to one of those two apical bristles present in the macropterous genera, and these again are most likely homologous to two of the six found in female Cretolixon ( Figs. 5b , 6e , 8a ).

Another important character of Cretolixon is the position of the hind wing cross vein cu-a ( Fig. 7 ), which is, similarly to its position in recent genera, clearly basal to the branching of the veins M and Cu (similar to Fig. 9b, c ). In Eorhopalosoma and most of the unpublished Burmese amber fossils of the family the cross vein cu-a is opposite or very near to the branching of the veins M and Cu (similar to Fig. 9a ). Brothers (1975) and Brothers and Carpenter (1993) regarded the basal position of the cross vein cu-a as the ancestral character state among aculeates and a distal position as the derived state but mentioned that several reversals back to the ancestral state occurred throughout the aculeates, and this might be true for Cretolixon and the recent rhopalosomatid genera as well.

Figures

Figure 3. Some diagnostic characters of Rhopalosomatidae. (a) Liosphex bribri Lohrmann (in Lohrmann and Ohl, 2010), female, paratype, apical bristles on basal flagellomeres. (b) Paniscomima kilombero Lohrmann, 2011, female, paratype, last metasomal segments with upcurved sting. (c) Liosphex varius Townes, 1977, male, mesosternal lobes covering the bases of the mesocoxae. (d) Olixon ferrugineum Krogmann et al., 2009, female, paratype, apical bristles on basal flagellomeres. (e) Rhopalosoma poeyi Cresson, 1865, male, last metasomal segments with upcurved parameres. (f) Fourth instar larva of a rhopalosomatid (Olixon?) wasp on a nemobiine cricket (Nemobiinae), collected in Florida, USA (deposited in the personal collection of Volker Lohrmann). Abbreviations: ab – apical bristle; FI, FII, FIII – flagellomere 1, flagellomere 2, flagellomere 3; T5, T6, T7 – metasomal tergite 5, metasomal tergite 6, metasomal tergite 7; msl – mesosternal lobe; msc – mesocoxa; mtc – metacoxa; pa – paramere. A cutout of panel (f) was first published in Fossil Record (Lohrmann and Engel, 2017).

Figure 5. Cretolixon alatum gen. et sp. nov., female, paratype (VL-Bu-04, UMB). (a) Habitus in lateral view. (b) Head and basal halves of antennae in oblique lateral view. (c) Mesosoma in lateral view. (d) Right protibia and protarsus. (e) Wings. The arrowheads indicate the apical bristles on second labial and third maxillary palpomeres (b).

Figure 6. Cretolixon alatum gen. et sp. nov., male and female, paratypes (male: SNSB-BSPG 2020 XCIII 25, SNSB; female: NIGP173865, NIGP). (a, c, d) Male. (a) Habitus in lateral view. (c) Base of right antenna. (d) Base of left antenna. (b, e) Female. (b) Habitus in slightly oblique dorsal view. (e) Partial right antenna (apex of FI to base of FIV). The arrowheads indicate the apical bristles on basal flagellomeres.

Figure 7. Cretolixon alatum gen. et sp. nov., male, holotype (MB.I 6500; ZMB). Venation of fore and hind wings (microtrichia omitted, drawing based on a photograph with a perspective similar to that of Fig. 4e).

Figure 8. Cretolixon alatum gen. et sp. nov., female, paratype (VL-Bu-04; UMB). (a) Basal half of left antenna. (b) Details of mouth parts (maxillary palpus highlighted in grey). (c) Details of mouth parts (labial palpus highlighted in grey). Abbreviations: FI, FII, FIII – flagellomere 1, flagellomere 2, flagellomere 3; G – gena; lp1,..., lp4 – labial palpomere 1,..., labial palpomere 4; M – mandible; mp2,..., mp6 – maxillary palpomere 2,..., maxillary palpomere 6; p – pedicel; sc – scape. Drawings based on Fig. 5b.

Figure 9. Some characters of Rhopalosomatidae. (a) Rhopalosomatidae, gen. et sp. indet., Burmese (Kachin) amber (ZMB; MB.I 6501), basal section of hind wing. (b) Liosphex boreus Lohrmann (in Lohrmann and Ohl, 2010), basal section of hind wing. (c) Rhopalosoma nearcticum Brues, 1943, basal section of hind wing. (d) Olixon banksii (Brues, 1922), mouthparts. (e) Liosphex longicornis Lohrmann (in Lohrmann and Ohl, 2010), mouthparts. (f) Paniscomima kilombero Lohrmann, 2011, mouthparts. (g) Paniscomima opposita Guidotti, 2007, male, paratype, head in dorsal view. (h) Paniscomima seyrigi (Berland, 1951), female, head in dorsal view. (i) Liosphex varius Townes, 1977, female, holotype, head in dorsal view. Abbreviations: ab – apical bristle; lp1,..., lp4 – labial palpomere 1,..., labial palpomere 4; mp1,..., mp6 – maxillary palpomere 1,..., maxillary palpomere 6. Panel (i) is reproduced with permission from copyright holder and was first published in Zootaxa (Lohrmann and Ohl, 2010); photo by David Wahl.

Figure 10. Distribution of the discussed characters among Rhopalosomatidae.The tree topology of the recent genera is based on Brothers and Carpenter (1993), Brothers (1999) (both: “rhopalosomatids” sister to Olixon), Guidotti (1999), and unpublished molecular data (Blaschke et al., unpublished results) (both: Olixon + (Liosphex + (Rhopalosoma + Paniscomima))).