THE LARVA OF MICROSTIGMUS COMES , 
WITH COMMENTS ON ITS RELATIONSHIP TO 
OTHER PEMPHREDONINE GENERA 
(HYMENOPTERA, SPHECIDAE)* 
By Howard E. Evans and Robert W. Matthews 
Museum of Comparative Zoology 
Compared to other Sphecidae, members of the Pemphredoninae 
exhibit an unusually wide spectrum of morphological features. Lar- 
val characters have suggested that simple division of the subfamily 
into the two tribes Psenini and Pemphredonini may not be ideal. 
(For discussion and for previous descriptions of the larvae of 
Pemphredoninae, or references thereto, see Evans, 1958, pp. 128- 
136; Evans, 1959, pp. 139-145, 167-168; and Evans, 1964, pp. 245- 
253.) Recently, larvae of another member of this group were obtained 
in the course of studies on the nesting biology of Microstigmus 
comes Krombein (see Matthews, 1967). Because, in addition, the 
genus exhibits many unique behavioral features, consideration of 
the larva and possible relationships of Microstigmus seem particu- 
larly appropriate. No previous larval descriptions exist for the 
genus; Myers’ (1934) drawings of the body and mandible of the 
larva of M. theridii fail to illustrate critical characters and hence 
are of little use to this discussion, although the features shown 
essentially agree with those of M. comes larvae. 
Description of mature larva of Microstigmus comes Krombein 
(Figures 1 to 3) 
Length 4 mm; narrowly fusiform, gradually tapered posteriorly, 
apical segment conically produced above the anus. Body slightly 
constricted at the intersegmental lines, more noticeably dorsally. 
Integument smooth, visible spines or setae absent even under high 
magnification. Spiracles minute, atrial walls completely smooth, 
entrance into the very slender subatrium unarmed. Head .47 mm 
wide, .44 mm long measured to apical margin of clypeus (about 
as long as wide when measured to apical margin of labrum) ; head 
devoid of setae and completely unpigmented except for the three 
brown apical mandibular teeth; parietal bands absent. Antennal 
orbits large, subcircular, about 55^ in diameter; antennal papillae 
well developed, about 25 /i long. Labrum short, its apical margin 
* Manuscript received by the editor April 6, 1968 
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