Extracted from: LaBerge, W. E., 1961. A Revision of the Bees of the Genus Melissodes in North and Central America. Part III (Hymenoptera, Apidae). The University of Kansas Science Bulletin, Vol. 43. 1-107.
This species closely resembles lupina, but it probably is more closely related to metenua. Both sexes of plumosa can be separated from those of lupina by the form of the flagella. The males of this species can be distinguished from those of metenua only with difficulty. The males of plumosa usually have the galeae dulled by delicate tessellation above, and usually have paler and more finely sculptured clypei than those of metenua.
Female. Measurements and ratios: N, 19; length, 10-12 mm,; width, 3.5-4.0 mm.; wing length, M = 3.40 - 0.098 mm.; hooks in hamulus, M = 12.32 - 0.154; flagellar segment 1/segment 2, M = 2.12 - 0.034.
Structure and Color: Color of integument as in M. lupina. Sculpturing and structure as in lupina with the following differences: clypeus with punctures averaging slightly smaller, more regular round in shape, usually with weakly developed median longitudinal carina in apical half, surface moderately shiny, with reticular shagreening; supraclypeal area with sparse large punctures, surface shiny, unshagreened or only slightly so; apical flagellar segment longer than broad; maxillary palpal segments in ratio of about 4.6:3.6:3.6:1.0; galeae with surface dulled by reticular shagreening but moderately shiny. Mesoscutum with posteromedian area often impunctate, surface shiny, not shagreened laterally and anteriorly; surface of scutellum unshagreened; mesepisternum with lateral surface with punctures separated by half or less of one puncture width, surface shiny, with sparse, fine shagreening. Metasomal tergum 1 with basal crowded punctures separated mostly by one puncture wdith or slightly more; tergum 2 with basal zone with punctures seperated mostly by slightly more than one puncture width, apical area with punctures extremely sparse and minute; pygidal plate U-shaped, apical half with sides subparallel, except rounded tip, and diverging only in basal half or less.
Hair: Color of vestiture as in M. lupina with the following dit-
ferences: tergum 4 without simple hairs apicomedially; terga 5
and 6 with brown hairs often much paler than in lupina, those of
tergum 6 often orange or golden-brown; sternal hairs golden me-
dially to white laterally; legs with hairs of inner surfaces of middle
and hind basitarsi and tibiae golden yellow to orange, on basitibial
plates pale brown; scopal hairs with rachises not extending much
beyond plumose part, usually with 6 or more branches on each
side of rachis; apicoposterior tibial scopal hairs usually not sinuate,
but occasionally so.
Male. Measurements and ratios: N, 20; length, 9-12 mm.; width,
2.5-4.0 mm.; wing length, M = 3.17 0.203 mm.; hooks in hamu-
lus, M=11.15 0.182; flagellar segment 2/segment 1, M = 4.28
Structure and color: Integumental color as in M. lupina except
vellow clypeus and base of mandible usually pale yellow and wing
veins reddish-brown to brown.
Sculpturing and structure as in lupina with the following difter-
ences: minimum length of first flagellar segment equals one-fifth
or more of maximum length of second segment; penultimate flagel-
lar segments 3 to 10 with shiny, elongate, dorsolateral depressions,
and often at base of segment 11 as well; maxillary palpal segments
in ratio of about 4.5:3.0:3.0:1.0.. Clypeus with crowded, round
punctures, in posteromedian area separated by less than one punc-
ture width, surface dulled by reticular shagreening, especially in
posterior half; supraclypeal area usually shiny and unshagreened.
or only slightly dulled by shagreening; galeae usually dulled above
by fine, reticular shagreening. Metasomal tergum 2 with depressed
basal area with small round punctures separated mostly by two
puncture widths; tergum 3 with interband zone with punctures sep-
arated by less than one puncture width; sternum 4 with apical flap
usually not emarginate or only extremely shallowly; sterna 2, 3 and
4 with median impunctate areas usually dulled by dense reticular
shagreening.Sternum 7 with median plate flat, not twisted to face laterally,
with apicolateral angle rounded, with short, broad neck, with
abundant short hairs ventrally. Sternum 8 usually with one or two
hairs apicomedially. Gonostylus less than two-thirds length of
gsonocoxite, capitate, with sparse short hairs ventrally near base,
none laterally; spatha as in lupina; penis valve with dorsolateral
lamella turned inwards to form a tooth directed medially near
spatha (Figs. 42-45).
Hair: Color of vestiture as in M. lupina with the following differ-
ences: metasomal tergum 2 with distal pale pubescent band often
not interrupted medially; terga 3 and 4 with distal pale pubescent
bands usually broader than in lupina.
Distribution. California, Oregon, Washington and North Dakota
(Fig. 4). It is possible that the single male collected in North
Dakota is misidentified and should be regarded as M. metenua (see
the discussion of this below under metenua). In addition to the
type material listed above, 6 females and 24 males have been
examined. The collection data for these are given in full, since
relatively few records are involved.