Entomobrya bicolor Guthrie, 1903

Katz, Aron D., Giordano, Rosanna & Soto-Adames, Felipe, 2015, Taxonomic review and phylogenetic analysis of fifteen North American Entomobrya (Collembola, Entomobryidae), including four new species, ZooKeys 525, pp. 1-75 : 21-22

Taxon classification Animalia Collembola Entomobryidae

Entomobrya bicolor Guthrie, 1903 Figs 2, 11, 12, 13A, 39

Description.

Body shape and color pattern. Body elongate and cylindrical. Only one reported color form in adults (Fig. 11A), dark brown or black pigment covering whole body except for a white band across Abd. 1, 2 and medial area of Abd. 3; Abd. 5 sometimes with 1+1 pale spots; legs, furcula, Abd. 6 pale, lacking all dark pigmentation; antennae lightly colored with brown or purple pigment, usually with a white area on distal half of 1st antennal segment. Juvenile pattern distinct from adult, yellow background without dark pigment except for eye patch; legs, furcula, Abd. 6 pale, lacking all dark pigmentation; antennae with light purple pigment. (Fig. 11B)

Head. Apical bulb of 4th antennal segment usually bilobed, rarely simple. Long differentiated smooth setae on ventral side of 1st antennal segment ≈ 3 –4× short seta. Prelabral setae ciliate. Ornamentation of the distal margin of the labral papillae with a single seta or spine-like projection (Fig. 2). Labial papilla E with lateral appendage reaching just above tip of papilla. Labial triangle in one individual with 2 small supplementary ciliate microsetae internal to M1. Dorsal head chaetotaxy as in Figure 12A: macrosetae An’ 0, A6, S’ 0, S6, Ps3, Ps5, Pi1, Pi3, and Pm1i always absent; An3a3 usually absent (present on one side in one specimen). Eyes G and H small and subequal. Eye patch with 5 setae.

Thorax. Thoracic chaetotaxy abundantly developed, highly variable with many supplemental macrosetae. Th. 2 macrosetae p6e and p6ep absent and macrosetae m4i2, m4i3 polymorphic (Fig. 12B). Th. 3 macrosetae a5e3, m4, m5p, a6i, a7, and m7 are absent (Fig. 12C). If present, m7 is always a mesoseta. Chaetotaxy of zone Pm of both thoracic segments densely packed with many supplemental macrosetae, forming wing-like patches of posterior setae extending near anterior row, typical for species within the Entomobrya bicolor complex (Fig. 3D). Position of pseudopores on Th. 3 atypical for Entomobrya , displaced anteriorly and closer to macrosetae a1, a2, and a3 than in other species.

Legs. Trochanteral organ with rectangular setal pattern and up to 37 setae. Unguis with 4 internal teeth; basal teeth enlarged and located approximately middle of inner claw length.

Abdomen. Abdominal chaetotaxy highly developed. Row of microsetae along entire posterior margin present in all segments (not displayed in figure). Abd. 1 with 12 macrosetae (Fig. 12D). Abd. 2 with 10-11 macrosetae: a2, a3, m3, m3e, m3ep, m3ep2, m3ea, m5, p5, and p6 always present. Abd. 2 macroseta m3eai sometimes present, m3ei always absent (Fig. 12E). Abd. 3 macrosetae a2, a3, m3, am6, pm6, p5, p6 present; a1 always absent (Fig. 12F). Abd. 4 elongated, with at least 22 inner macrosetae (Fig. 12G), number of macrosetae extremely variable between individuals and within individuals (Fig. 13A). Position of pseudopores on Abd. 4 unstable, even varying with respect to macroseta and bothriotricha between sides on same individual (Fig. 13A). Mucronal teeth subequal; mucronal spine enlarged.

Remarks.

Entomobrya bicolor adults can be easily distinguished by the unique color pattern described above combined with the absence of head macroseta Ps5 (see Table 2 for additional diagnostic characters). Adults have a single, highly stable color form that is easily recognizable and perfectly acceptable for diagnosis (Fig. 11A). Molecular data from Katz et al. (2015) revealed that a small specimen found with Entomobrya bicolor , which was completely yellow and lacking all dark pigment, is the juvenile form of Entomobrya bicolor (Fig. 11B). The Entomobrya bicolor juvenile color form has never been reported in the literature. Unfortunately, it may be difficult to diagnose juvenile members of this species if collected without adults present in the sample.

Christiansen (1958b) placed this species in what he termed "the Entomobrya bicolor group"; a complex of three closely related species; Entomobrya quadrilineata , Entomobrya decemfasciata , and Entomobrya bicolor . This group is characterized by a highly elongate, cylindrical body, a relatively long furcula, antennae and legs, and by their abundant and highly variable chaetotaxy; many duplicate, supplementary macrosetae, distinctive and augmented setal patterns in thoracic zone Pm, expanded chaetotaxy of Abd. 4, and high levels of asymmetry (Fig. 13A). The extreme setal variation obscures potentially informative characters and results in a lack of discrete, useful diagnostic chaetotaxy between species in this complex. The absence of head macroseta Ps5 is the only character (other than color pattern) that differentiates Entomobrya bicolor from Entomobrya decemfasciata and Entomobrya quadrilineata . Color pattern is critical for species diagnosis within this complex. See Table 5 for a summary of the important diagnostic characters to separate species in this complex.

Distribution.

Endemic to North America (Suppl. material 2: C).

Material examined.

USA: 9 on slides, 6 in vial, Illinois, Henderson Co., Big River State Forest (41.03435,-90.91620), vacuum sand prairie, 8.vi.2011 (C. H. Dietrich).