Rhopalosomatidae Ashmead, 1896

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 : 218-223

Family Rhopalosomatidae Ashmead, 1896

Rhopalosomidae Ashmead 1896: 303. Type genus: Rhopalosoma Cresson, 1865 . (Ashmead preferred his form of the family name to Rhopalosomatidae (see footnote on page 303). In doing so, he used an incorrect spelling for the stem of his proposed new family name. Since the correct combining stem is “Rhopalosomat-”, the family name was consequently corrected to Rhopalosomatidae by Brues (1922)).

Rhopalosomatidae Ashmead : Brues, 1922: 102 (and most subsequent authors).

V. Lohrmann et al.: † Cretolixon – a remarkable new genus of rhopalosomatid wasps 219

Diagnosis (modified from Krogmann et al., 2009)

Among aculeate Hymenoptera , Rhopalosomatidae can be easily identified by the following combination of characters: basal flagellomeres with distinct apical bristle(s) ( Figs. 3a, d , 4d , 5b , 6c–e ; very small or completely reduced in many Olixon ), mesosternum with posterad paired lobes covering the bases of the mesocoxae ( Figs. 3c , 4c ), male parameres upcurved ( Fig. 3e ), female sting upcurved ( Fig. 3b ), female tarsomeres laterally widened ( Fig. 5d ), female pretarsus with arolium and cuticular plate greatly enlarged and claw sensor elongated.

Rhopalosomatid larvae are easily recognized by their habit as ectoparasitoids of true crickets ( Gryllidae ) ( Fig. 3f ), unique within Hymenoptera .

With only eight enclosed fore wing cells (C, R, 1Cu, 1R1, 2R1, 1Rs, 1M, and 2Cu), the wing venation of fully winged rhopalosomatid species may superficially resemble those of some other aculeates, e.g., extinct Formiciinae, Sphecomyrminae, and some Myrmeciinae, whereas members of the genus Olixon are brachypterous or apterous. However, Rhopalosomatidae can be distinguished from them by the very narrow fore wing costal cell, the relatively large and oblique fore wing cell 1M, and the position and form of the hind wing veins Rs ∗ (short, straight, and reclivous but angled or curved in most Rhopalosoma ) and cu-a (basal or opposite of the branching of veins M and Cu).

Sexual dimorphism

Apart from the genital morphology, males and females can be differentiated by the following: the number of flagellomeres – females have 10, males have 11; the number of visible metasomal tergites – females have 6, males have 7; the form of the tarsomeres II–IV – cylindrical for males and dorsoventrally flattened for females; the absence or presence of tarsal plantulae – absent in females, present in males; and the form of the apex of the pretarsal claws – simple in females, bifid in males.

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 4. Cretolixon alatum gen. et sp. nov., male, holotype (MB.I 6500; ZMB). (a) Habitus in lateral view. (b) Head in slightly oblique frontal view.(c) Mesosoma in lateral view.(d) Partial right antenna.(e) Wings.Abbreviations:ab – apical bristle; FI, FII, FIII – flagellomere 1, flagellomere 2, flagellomere 3; lo – lateral ocellus; oc – occipital carina; p – pedicel; sc – scape. The arrowheads indicate the apical bristles on third maxillary palpomeres (c) and basal flagellomeres (d).

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.