Nebritus
powelli Webb & Irwin
(Diptera: Therevidae: Therevinae)
Derivation
of name.
This species in named in honor of Jerry A. Powell, University
of California, Berkeley, who collected many of the specimens.
Diagnosis.
Males and females of Nebritus powelli are very similar
to N. tanneri in having the scape cylindrical, dark reddish
brown with gray pruinosity; the length of the scape less than
0.80 mm; the length/width ratio of the scape greater than 3.5.
Nebritus powelli is separated from N. tanneri in
having the thorax with a broad median band of white setae; the
scutellum with a lateral patch of white setae; and sternite 8
in males is subquadrate with the posterior margin shallowly emarginate;
the gonocoxite lacks a distinctive posteromedial patch of black
setae in ventral view; and the ejacuatory apodeme is narrow, not
expanded anteriorly.
Description
of holotype male
(MEI 006335). Body length 5.8 mm.
Head.
Length 0.9 mm. Ocellar tubercle black, glossy; ocellar setae black,
elongate, scattered. Eyes reddish brown, median margin of eyes
straight.. Frons (Fig. 13) brownish
gray pruinose on dorsal two-thirds and surrounding lateral half
of antennal bases and dark reddish brown to black, glossy on ventral
third of frons; a dark brown pruinose area exists dorsolaterally
on frons and silver pile extends laterally from antennal bases
to margin of eyes; setae black, elongate, scattered over entire
frons. Antenna (Fig. 14) dark
brown, brownish gray pruinose; setae dark brown, scattered over
scape, pedicel and basally on flagellum; macrosetae black, scattered
on scape; length of antenna 1.1 times head length; length of scape
0.46 mm, 3.8 times width, 4.6 times length of pedicel; length
of pedicel 0.10 mm, 0.8 times width; length of flagellum 0.38
mm, 2.7 times width, 0.8 times length of scape; style length 0.04
mm. Parafacial with dense, white to gold pile; tentorial pit large,
dark reddish brown, glossy. Genal setae white. Maxillary palp
dark brown, gray pruinose; length 0.40 mm, 4.0 times width; setae
dark yellow.
Thorax.
Macrosetae: np 3, sa 1, pa 1, dc 1, sc 2. Dark brown, gray pruinose;
mixture of white, lanceolate, subappressed setae and dark brown,
elongate setae over entire dorsum; vittae dark brown, dorsocentral
and dorsolateral vittae separated by gray pruinose stripe. Postpronotal
lobe concolorous with thorax; setae pale yellow, elongate. Prosternal
setae white. Pleuron dark brown, dense gray pruinose; setae white,
elongate, abundant on propleuron, scattered over entire anepisternum
although more dense dorsally, scattered over entire katepisternum
although more abundant along anterior margin. Scutellum dark brown;
setae white to pale yellow with lateral patch of white setae.
Laterotergite dark brown, dense gray pruinose; setae pale yellow
with scattered dark brown setae.
Wing.
Length 4.3 mm, 3.3 times width; opaque, pale smoky brown, concolorous;
pterostigma slightly darker than membrane. Halter dark brown,
stalk yellowish brown.
Legs.
Coxae dark brown, dense gray pruinose, apical macrosetae dark
brown. Femora dark brown, gray pruinose; setal pattern a mixture
of scattered, white, and dark brown, elongate setae and white,
appressed, lanceolate setae. Tibiae dark yellowish brown, apical
half of foretibia, apical fourth of middletibiae, and apex of
hindtibia dark brown. Tarsi dark brown, basal fourth of hind basitarsus
dark yellowish brown.
Abdomen.
Dark brown, gray pruinose, concolorous; dorsal setae dark brown,
subappressed; lateral setae dark brown, elongate with scattered
pale yellow lanceolate setae.
Terminalia
(Fig. 15-20). Tergite 8 broad;
posterior margin broadly emarginate. Sternite 8 subquadrate, posterior
margin shallowly emarginate. Gonocoxite lacks posteromedian patch
of black setae as seen in ventral view. Ejaculatory apodeme narrow,
not expanded anteriorly.
Variation.
Body measurements given in table.Thorax.
Macrosetae: np 3, sa 1-2, 2, pa 1, dc 1, sc 2.
Description
of Female
Similar to male with following exceptions. Body measurements given
in table.
Head.
Ocellar tubercle dark reddish brown, dark gold pruinose; setae
dark reddish brown, scattered. Frons dark reddish brown, dorsal
half dark gold pruinose, ventral half silver gray pruinose; dark
yellow and dark reddish brown setae, moderately long, scattered.
Maxillary palp pale yellowish brown.
Thorax.
Macrosetae: np 2-3, 3, sa 2, pa 1, dc 1-2, 1 sc 2. Dark gold and
black setae on mesonotum, dark gold setae subappressed.
Legs.
Foretibia dark yellowish brown, apical fourth dark reddish brown.
Abdomen.
Dark reddish brown, dense gray pruinose along posterior third
of each tergite.
Terminalia
(Fig. 21-22). Furca (Fig.
22) oval; anterior and posterior margins truncate; lateral
margins rounded.
Immature
Stages
Larva
(N=2) (Figs. 23-26): Length 0.50-0.54
mm, 1.5 times longer than wide; metacephalic rod elongate, posterior
third clavate, length 0.82-0.84 mm, 1.6 times length of head.
Prothoracic spiracle (Fig. 25).
Posterior spiracle (Fig. 26).
Pupa
(N=4) (Figs. 27-28). Length 7.8-9.3,
8.7 mm, width 1.8-2.2, 2.0 mm. Alar process not spinose. Labial
sheath tapered ventrally, bisecting proboscial sheath. Length
of antennal sheath 0.42-0.46, 0.45 mm, apical spine absent.Thoracic
spiracle short, truncate apically; length 0.14-0.21, 0.17 mm,
. Posterior spines elongate, not divergent apically, length 0.27-0.36,
0.32 mm. Dorsal spines on abdominal segments I-VII and ventral
spines on segment II-VII fine, not fused basally. Abdominal spiracles
on segments I-VII moderately thick, tubular.
Seasonal
Activity. In the specimens examined, adults were collected
from 10 January to 19 July, with several specimens collected on
dunes and on Salix sp.
Distribution.
Nebritus powelli is known only from the coastal dunes of
central California. (Map)
text
from Webb & Irwin 1991a
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Nebritus powelli index | Begin
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