Megachilini
Creators: name: Rozen, Jerome G.
name: Praz, Christophe J.
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Hymenoptera
Megachilidae

description: COMPARISON WITH MEGACHILINI
The description of the larvae of the Osmiini, above, is based on the material treated in the following key. However, this description cannot be relied upon to distinguish osmiine larvae from those of other nonparasitic 6 members of the entire Megachilinae because of the large size of the subfamily and lack of information concerning mature larvae of so many included taxa. It was therefore decided to undertake an exploratory character comparison between the description of the Osmiini, above, and the description of the Megachilini as presented by Rozen and Kamel (2007), augmented by the more complete evaluation of the genus Megachile in Rozen et al. (2016). Such a comparison might be useful in two ways: it might test the usefulness of larval characters in evaluating phylogenetic relationships in the subfamily in general, and specifically it might test the hypothesis that Ochreriades is the sister to the lineage that gave rise to the Osmiini and Megachilini, one of the topologies recovered in Praz et al. (2008).
No consistent differences were detected regarding larval head features between the two tribes. In body shape, Megachilini were consistently linear in lateral view with the largest segments toward the rear. With Osmiini body shape was highly variable, with one group (Ashmeadiella, Chelostoma, and Ochreriades) having more slender bodies, widest at midbody and tapering toward both ends (figs.12–18, 22, 23, 27). With other osmiines, the posterior end of the abdomen was extensively enlarged (figs. 1, 20, 24, 26, 28) or in other ways (figs. 3, 4, 20, 21) distinguishable from the three genera identified above.
One feature dealing with body vestiture may shed light on the relationship between Ochreriades on one hand with the Osmiini and Megachilini on the other hand. Rozen et al. (2016) pointed out that in Megachilini body vestiture consists of only setae and no spicules. However, in the Osmiini, mature larvae of some taxa have a body vestiture of both setae and spicules while others have setae alone. Larval Ochreriades has only body setae (Rozen et al., 2015). Among the various branches of the Megachilidae, larvae of Pararhophitini are known to have both types of body vestiture (McGinley and Rozen, 1987). In the Fideliini both types of vestiture are found in Fidelia (Rozen, 1970) and Parafidelia (Rozen, 1977), but in Neofidelia, only body setae are found (Rozen, 1973a). Among the Lithurgini both types of body vestiture have been reported for Lithurgus, Lithurgopsis, and Trichothurgus (Rozen, 1973b; Rozen and Hall, 2014). If it is assumed that the widespread occurrence of two types of body vestiture in all the
6 Cleptoparasitism has evolved a good many times in the Megachilidae, possibly resulting in a number of de novo appearances of parallel anatomical features. Furthermore, larvae of presumed cleptoparasitic osmiines have not yet been studied. To simplify analysis, only nonparasitic groups have been considered here but are referenced in other places in the paper.
basal branches of the family is evidence that it is the primitive condition in the Megachilidae, then the occurrence of setae alone is derived.
However, the presence or absence of body spicules may be a labile feature in megachilid bees, as evidenced by absence of spicules in Neofidelia mentioned above, as well as the following: in the Anthidiini Trachusa larreae (Cockerell) (Rozen and Hall, 2012), Anthidium chilense (Urban) (as Notanathidium (Allanthidium) chilense, Rozen, 2015), and Stelis (S.) elongativentris Parker (Rozen, 1987) are reported to have setae and spicules, whereas Stelis (S.) phaeoptera murina Pérez (Rozen and Kamel, 2009) and Stelis (S.) ater Mitchell (Rozen and Hall, 2011) have only setae.
And yet another matter remains obscure. It has been postulated that body vestiture in megachilid bees enables the mature larva to move around in its cell to finish feeding, to position its fecal deposits, and to manufacture its cocoon (Rozen and Hall, 2011, 2012, 2014; Rozen, 2013a). In most of these cases two types of vestitures are involved: spicules and setae. We also know that with some taxa setae alone are involved (e.g., Ochreriades, Megachile). We do not understand the differences in the function of these two mechanical systems that accomplish the same thing. There is more work to be done.
KEY TO MATURE LARVAE OF OSMIINE SPECIES DESCRIBED HEREIN EXCLUSIVE OF OSMIA
The preparation of this key was an attempt to analyze larval features that might be employed to distinguish between the various genera of osmiines. As indicated in the introduction, mature larvae of Osmia are too poorly known at this time to be generically characterized. Furthermore, larval representatives of only two of the subgenera of Hoplitis are known. All other osmiine taxa whose larvae are treated in the paper can be found below except for Atoposmia copelandica, the single specimen of which was poorly preserved. Unknown is whether the head of the postdefecating form of this species normally retracts into the prothorax, as does the head of Atoposmia hypostomalis, as mentioned above in the section on Special Anatomical Features.
1. Intersegmental lines deeply incised with caudal annulets of anterior abdominal segments tending to override anterior part of following cephalic annulets (fig. 3); body integument of postdefecating larva relatively stiff, so that body shape retained even after clearing (all species of Hoplitis dealt with herein except for H. xerophila)........................ 2
– Intersegmental lines normally to weakly incised, so that segments not overriding one another as described above (figs. 4, 12–28); integument of postdefecating larva relatively soft, so that body of cleared specimen tending to flatten when not submerged in glycerin........ 5
2(1). Antenna projecting as far as clypeus in lateral profile (fig. 11); cephalic annulet of abdominal segments 3 and 4 each with deep transverse groove resulting in formation of median, strong, posteriorly directed intersegmental tubercle (fig. 8)...................
........................................ Hoplitis (Alcidamea) biscutellae (Cockerell) – Clypeus projecting farther than antenna in lateral profile (figs. 9, 10); cephalic annulet of abdominal segments 3 and 4 with (figs. 6, 7) or without (fig. 5) transverse groove, but if with groove never forming posteriorly directed intersegmental tubercle.............. 3
3(2). Mandibular teeth, at least usually, apically rounded; vestiture of lateral lobe of abdominal segment 8 without pigmented spicules, consisting of only fine setae (although if broken, setae might be confused with spicules)...... Hoplitis (Alcidamea) fulgida (Cresson)
– Mandibular teeth apically acute, short to elongate; vestiture of lateral lobe of abdominal segment 8 consisting of both setae and pigmented spicules.......................... 4
4(3). Vertex in lateral profile slightly curved (fig. 9), without angle or protrusion; cephalic annulet of abdominal segment 3 without transverse groove (fig. 5)............................................................. Hoplitis (Alcidamea) hypocrita (Cockerell)
– Vertex in lateral profile either bent (as in fig. 11) or bearing low protuberance (fig. 10); cephalic annulet of abdominal segment 3 with distinct, small to large transverse groove............................................ Hoplitis (Alcidamea) producta (Cresson) Hoplitis (Alcidamea) sambuci Titus Hoplitis (Alcidamea) uvulalis (Cockerell)
5(1). Postdefecating larva in lateral view with thickest part of body near midbody and posterior part of body gradually tapering (figs. 12–18, 21–23, 27); elevation of caudal annulets tending to persist posteriorly at least to abdominal segment 7; head size except for Haetosmia vechti (fig. 21) tending to be small to very small relative to body size (figs. 12–19, 22, 23)......... 6
– Postdefecating larva in lateral view with thickest part of body well posterior to midbody and posterior part of body ending more abruptly (figs. 20, 24–26, 28); elevation of caudal annulets tending to be lost beyond abdominal segment 5; head size tending to be moderate relative to body size (figs. 4, 20, 24–27)..................................... 10
6(5). Caudal annulets without midline dorsal tubercle, so that caudal annulet uniformly setose; head size relative to body size small (figs. 12–16, 18) to very small (figs. 17, 22, 23)....... 7
– Caudal annulets of abdominal segments 1–4 with elevated midline tubercles that lack setae (fig. 21, arrows); head size relative to body size moderate (fig. 21)......... Haetosmia vechti Peters
7 (6). Head size very small relative to body size (figs. 17, 22)............................ 8
– Head size relative to body size larger (figs. 12–16, 18) than that of Chelostoma ................................. Ashmeadiella (all species treated herein except for A. opuntiae) Ochreriades fasciatus (Friese)
8(7). Antennal papilla longer, length about 3 times basal diameter..................................................................... Ashmeadiella (A.) opuntiae Cockerell
– Antennal papilla shorter, length about 2 times basal diameter......................... 9
9(8). Spiracular atrium without spicules... Chelostoma (Gyrodromella) rapunculi (Lepeletier)
– Spiracular atrium with spicules....... C helostoma (Prochelostoma) philadelphi (Robertson)
10(5). Abdominal segment 8 with lateral lobe bearing about 25 inconspicuous setae/spicules; body form of postdefecating larva robust (fig. 28)..... Osmia (Hoplosmia) anceyi (Pérez)
– Abdominal segment 8 with lateral lobe bearing 15 setae/spicules or fewer; body form variable...................................................................11
11(10). Body vestiture consisting of two lengths, i.e., longer, tapering setae and shorter setae/ spicules of uncertain structure; head retracted into pronotum, so that only front visible in lateral view (fig. 20)................ Atoposmia (Eremosmia) hypostomalis (Michener)
– Body vestiture consisting of only setae; head normally exserted (figs. 4, 17)............ 11
11(10). Head of normal size (figs. 24, 25) compared to body; caudal annulets without bilobed median tubercle lacking setae (fig. 24); body setae pigmented, unusually bristlelike and stiff, stout basally, tapering evenly to fine, sharp apices; these setae arising from conspicuous alveoli............................... Heriades (Heriades) truncorum (Linnaeus)
– Head size small (fig. 4) relative to body size; caudal annulets of abdominal segments 1–4 with posterior edge produced as low bilobed tubercle lacking setae (fig. 4); body setae normally slender, fine, inconspicuous, like those of other Hoplitis ............................................................. Hoplitis (Proteriades) xerophila (Cockerell)
DESCRIPTIONS OF OSMIINE LARVAE ARRANGED ALPHABETICALLY BY GENERIC NAME
POSTDEFECATING LARVA OF ASHMEADIELLA (ASHMEADIELLA) MELILOTI MELILOTI (COCKERELL)
Figure 12
DIAGNOSIS: As indicated by the key, above, treated larvae of Ashmeadiella, Chelostoma, and Ochreriades are so similar that they can scarcely be distinguished. Only those of Chelostoma because of their extremely small head are keyed separately. There exists some variation in the number of atrial spicules, width of the salivary lips, degree of expression of elevation of caudal annulets, and perhaps in body size. However, such features are difficult to quantify and therefore of little diagnostic value. Features shared by these three taxa include slender body form with thickest part of body being the midsection and with the body gradually, evenly narrowing at both ends. Furthermore, they display no middorsal intersegmental tubercles lacking vestiture. There is also a tendency for the caudal annulets to maintain their prominence with respect to the cephalic ones toward the posterior end of the body, contrary to many of the other osmiine taxa.
The following description of A. m. meliloti was originally based on the specimens from Bear Lake, Utah, collected and identified by Parker as A. meliloti? Subsequently after examination of the Krombein material from Portal, Arizona, no features could be found to distinguish the specimens from the two localities.
DESCRIPTION: Head: Head moderately small in relation to body size (fig. 12); oriented in normal, hypognathous position relative to thorax. Labrum faintly pigmented except on some specimens transverse labral sclerite somewhat darker but unevenly so; maxillary sclerites faintly pigmented; salivary lips weakly to deeply pigmented; antennal papilla and maxillary and labial palpi all uniformly moderately pigmented to almost unpigmented. In lateral view, clypeus not projecting beyond frons, antenna not arising from prominence, and labrum not extending much beyond clypeus. Antennal papilla distinctly but not strongly pigmented, moderately large and elongate, longer than twice basal diameter, bearing approximately three sensilla apically. Labral sclerite unevenly pigmented.
Mandibular apex approximately parallel sided in outer views; both teeth on postdefecating larva narrowly acutely pointed with apices well separated; dorsal apical edge of dorsal tooth faintly, irregularly uneven; apical concavity defined; cuspal area not projecting; outer mandibular surface with single conspicuous long curved seta near base. Labial apex very narrow in frontal view; premental sclerite absent. Salivary lips very narrow, with inner surface questionably bearing parallel longitudinal grooves; width of lips slightly less than distance between bases of labial palpi.
Body (fig. 12): Body vestiture without spicules, consisting only of slender, pale, moderately elongate setae, tapering to fine points, arising from small but distinct alveoli; these setae inconspicuous; setae moderately abundant on elevated dorsal surfaces of thorax and widely scattered on anterior ventral surface of thorax; some setae present on dorsal surfaces of caudal annulets of abdominal segment 8, 9, and 10, on ventral surface of abdominal segments 8, 9, and 10; those below anus short and inconspicuous; dorsal surface elsewhere with scattered short inconspicuous setae; lateral lobe of abdominal segment 8 (i.e., area below level of spiracle) with approximately 8 setae. Body form of postdefecating larva moderate in lateral outline between robust and slender (fig. 12); body segments in lateral view gradually increasing in diameter with abdominal segments 3 to 5 having greatest diameters; caudal annulets of most body segments projecting farther than cephalic annulets and surprisingly uniform in appearance; middorsal intersegmental tubercles totally absent. Body form of predefecating larva unknown. Spiracles with pigmented peritreme, subequal in diameter; atrium globular with width somewhat greater than depth, projecting above body wall, with rim; diameter of atrial opening about 3 times radial width of peritreme; atrial inner surface smooth or nearly so; primary tracheal opening with collar; subatrium long, with about 14–18 chambers; chambers increasing slightly in size from body surface inward.
MATERIAL EXAMINED: Four postdefecating larvae: Utah: Rich Co.: Bear Lake, 1973 (F.D. Parker) #7805. 6 postdefecating larvae: 7 AZ: Cochise Co.: Portal VII-20-1959, V-19-1961, VI-10, 15, 19-1961 (K. V. Krombein).
POSTDEFECATING LARVA OF ASHMEADIELLA (ASHMEADIELLA) ARIDULA COCKERELL
Figure 13
The larva of this species is similar to that of A. m. meliloti, although the pigmentation is reduced and the body size is smaller. The peritreme is not or is only scarcely pigmented, and the atrial surface is more clearly ringed and with scattered small spicules that are less obvious than those of A. breviceps.
MATERIAL EXAMINED: Six postdefecating larvae: CA: Fresno Co.: 6 mi S Kerman, VIII-15- 1962 (P. Torchio) #399. Nesting in 3/16″ soda straw in competition with Megachile rotundata.
7 Krombein (1967) made no distinction between postdefecating larva, resting larva, and prepupa. FIGURES 12–19. Entire larvae of Ashmeadiella, lateral view. 12. A. m. meliloti. 13. A. (A.) aridula. 14. A. (A.) bigeloviae. 15. A. (A.) bucconis denticulata. 16. A. (A.) c. cactorum. 17. A. (A.) opuntiae. 18. A. (A.) occipitalis (postdefecating form). 19. A. (A.) occipitalis (defecating form).
POSTDEFECATING LARVA OF ASHMEADIELLA (ASHMEADIELLA) BIGELOVIAE (COCKERELL)
Figure 14
The larva of this species can not be distinguished from that of A. m. meliloti. The two specimens examined were close to pupation, which apparently made spiracles impossible to identify; their position is approximated (fig. 14).
MATERIAL EXAMINED: One postdefecating larva (with pupal integument starting to form): AZ: Maricopa Co.: Scottsdale, V1-10-1961 (K. V. Krombein) resting, H 22, cell 1. 1 postdefecating larva (with pupal legs visible) AZ: Cochise Co.: Portal, V-19-1961 (K. V. Krombein) resting, G 25, cell 1.
PREDEFECATING LARVA OF ASHMEADIELLA (ASHMEADIELLA) BUCCONIS DENTICULATA (CRESSON)
Figure 15
The single available specimen of this species had fecal material in its hind gut and also some apparently in the midintestine, indicating that it was preserved before it had reached the postdefecating stage. Unfortunately, the specimen tore apart while being cleared, so that placement of spiracles are approximate in figure 15, but other important features could be observed, none of which seemed to differ from those of postdefecating A. m. meliloti.
MATERIAL EXAMINED: One defecating larva: AZ: Cochise Co.; Portal, V1-10-1961 (K. V. Krombein) mature, C 15, cell 2.
description: Published as part of Rozen, Jerome G. & Praz, Christophe J., 2016, Mature Larvae and Nesting Biologies of Bees Currently Assigned to the Osmiini (Apoidea: Megachilidae), pp. 1-48 in American Museum Novitates 2016 (3864) on pages 10-16, DOI: 10.1206/3864.1, http://zenodo.org/record/4566088