Monomorium minimum subsp. cyaneum Wheeler 1914

Seifert, Bernhard, 2025, The Monomorium carbonarium species group in the Nearctic and Europe (Hymenoptera: Formicidae), Soil Organisms (Toronto, Ont.) 97 (1), pp. 55-84 : 72-73

Monomorium minimum subsp. cyaneum Wheeler 1914

[syn. nov., type investigation]

This taxon has been described from the state of Hidalgo, Mexico based on “numerous workers and females taken at Guerrero Mill under stones in rather damp places on the sides of the canyons” ( Wheeler 1914). Morphometrically investigated was a paratype wingless gyne plus three paratype workers labelled “ Guerrero Mill. Hidalgo. Mexico W.M. Mann”, “ PARATYPE ”, “WM Mann 1954 Collection”; depository NMNH Washington. The three paratype workers were allocated to the Monomorium ergatogyna cluster with p = 0.9965 in a wild-card run of a 3-class LDA considering the species Monomorium carbonarium , M. ergatogyna and M. gallicum n.sp. ( Tab. 1). The paratype wingless gyne was placed within the M. ergatogyna cluster in a PCA ( Fig. 7 ). Note: There are some 180 workers in NMNH Washington labelled by DuBois as paratypes of Monomorium cyaneum . These belong to two species (see Tab. 1) and cluster either with M. ergatogyna or M. carbonarium . Since the lectotype gyne (designated by DuBois 1986) and workers associated to this gyne were not investigated, it cannot be excluded that M. cyaneum is instead a junior synonym of M. carbonarium . However, because the ratio of M. ergatogyna vs. M. carbonarium in morphometrically investigated worker samples from Mexico as a whole was 5: 1, the synonymization stated above appears more probable.

All material examined. Numeric phenotypical data were taken in 30 samples with 95 workers and 26 gynes. The material came from Mexico (4 samples) and the USA (26 samples). For details see supplementary information SI1, SI2 and SI3..

Geographic range. Widely distributed over the USA south to Mexico and overall more frequent than M. carbonarium . Vouchers from the USA include the states California, Nevada, Idaho, Texas, Mississippi, Tennessee and Virginia. Altitudinal records range from sea level up to 2900 m (at 20°N in Mexico) .

Description: --Worker ( Tab. 3; Figs. 23, 24 ; key). Very small, CS 464 ±21 µm. Head moderately long, CL/CW 1.204 ± 0.024. Dents on clypeal margin moderately long (ExCly/CS 4.58 ± 0.68%), not very acute and moderately distant (ClSpD/CS 10.38 ± 0.96%). Frontal carinae moderately distant and slightly diverging frontad (FL/ CS 0.274 ± 0.008, FR/CS 0.263 ± 0.008, FL/FR 1.041 ± 0.026). Eye and preocular distance moderately large (EL/ CS 0.199 ± 0.009, PrOc/CS 0.224 ±0.009). Scape and funiculus segments moderately long (SL/CS 0.817 ± 0.022, Fu2/CS 6.36 ± 0.36%, Fu3/CS 4.83 ± 0.28%). Mesosoma short and rather narrow (ML/CS 1.161 ± 0.032, MW/CS 0.567 ± 0.015). Metanotal groove moderately deep, MGr/ CS 4.63 ± 0.70%. Dorsum and slope of propodeum in profile forming a convex curve. Petiole rather wide but moderately high and long (PeW/CS 0.282 ± 0.017, PeH/ CS 0.361 ± 0.010, PeL/CS 0.425 ± 0.013). Postpetiole moderately wide and high (PpW/CS 0.317 ± 0.013, PpH/ CS 0.284 ±0.011). All body surfaces with exception of few rugulae on frontal lobes, ventral mesopleuron, ventrolateral area of metapleuron and genae glabrous and shiny. All body parts homogenously dark brown to jet black; mandibles, lateral clypeus and antennal funiculus lighter brown.

--Gyne ( Tabs. 5 and 6): Both winged and wingless gynes are developed but the latter are much more frequent. The sparse material available, in particular of winged gynes, does not allow to propose diagnostic determination characters but at least the wingless gynes are separated from those of M. carbonarium and gallicum n.sp. by a PCA considering all 19 characters ( Fig. 7 ).

Taxonomic comments. The worker is very similar to M. carbonarium and does not show any diagnostic character. As result, the separation from M. ergatogyna and M. gallicum n.sp. is only possible by stepwise multivariate analyses ( Figs. 31-34 , for details see above).

Biology. The unresolved species delimitation in the past does not allow to use literature sources and I can only refer here to the sparse information connected with material determined in this revision. Wheeler (1914) reported his subspecies cyaneum to occur in rather damp and moist places within a xerothermous environment. Four nest samples collected in California by Lorenzo Fraysse (SaNo 115-118) were found in chaparral – twice under stones and once each under grass and in a wet mossy path embankment. Two nest samples collected in Nevada were found in semideserts. Winged gynes are much rarer than wingless gynes and young winged gynes were observed in the investigated material 2 July 1919, 26 July 1942.

Monomorium compressum Wheeler 1914

Figures

Figure 7. Principal component analysis of wingless gynes of Monomorium carbonarium (black dots), M. ergatogyna (white rhombs) and M. gallicum n.sp. (black crosses). Acronyms indicate the placement of type specimens: W – holotype of M.wheelerorum, C – paratype of M. cyaneum, T – types from holotype nest of M. trageri, G – types from holotype nest of M. gallicum n.sp., E – types from holotype nest of M. ergatogyna.

Figure 24. Lateral aspect of Monomorium carbonarium; Netherlands: Zwartevaal, 2022

Figure 31. NC-part.hclust analysis of workers of Monomorium carbonarium (black bars), M. ergatogyna (blue bars), and M. gallicum n.sp. (red bars). The empty bar refers to outliers.

Figure 32 (left). Sample means of principal component analysis considering 12 characters measured in workers of of Monomorium carbonarium (black dots), M. ergatogyna (white rhombs), and M. gallicum n.sp. (black crosses). Figure 33 (right). Sample means of a linear discriminant analysis considering 12 characters measured in workers of of Monomorium carbonarium (black dots), M.ergatogyna (white rhombs),and M.gallicum n.sp. (black crosses).Acronyms indicate the placement of type specimens: CA – type sample of M.carbonarium, CY – paratype sample of M. cyaneum, EM – paratype sample of M.emersoni, ER – type sample of M. ergatogyna, GA – type sample of M.gallicum n.sp., TR – type sample of M.trageri, WH – type specimen of M. wheelerorum.

Figure 34. Results of three exploratory data analyses (EDAs) of worker samples ofMonomorium carbonarium (blackbars) and M.ergatogyna (grey bars).Shown is the NC-part.hclust dendrogram and results of NC-NMDS.kmeans and Principal Component Analysis.The empty space in the NC-part.hclust bar refers to outliers. The mean error of the three EDAs relative to the final species hypothesis is 5.0%.