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Psyche 
[Vol. 89 
knife on a Porter-Blum-Microtome MT-1 (Sorvall®), stained using 
Mallory’s Azure II-Methylene Blue (Richardson et al., 1960), and 
examined using a light microscope. 
Results and Discussion 
The ectal mandibular gland in P.fuscatus females is similar to the 
ectal mandibular gland Nedel (1960) described for V. germanica. 
The gland reservoir, which lies appressed to the gena, opens at the 
base of the mandible via a long, flattened, sclerotized duct. Gland 
cells can be seen on the outer surface of the reservoir (Figure la). 
The sclerotized duct of the reservoir opens on to the mandibular 
surface just above a brush of bristles (Figure lb). The bristles may 
be mechanoreceptors and may also serve to increase the surface area 
for evaporation of the glandular secretion. A scallop of cuticle 
extends ventrally from the gena, covering the brush when the man- 
dible is closed. When the mandible is opened even slightly the brush 
is exposed on the front of the face (Figure 2). 
The position of the ectal mandibular gland opening suggests a 
social rather than a physiological function. Because it does not open 
into the mouth, this gland is probably not a source of digestive 
enzymes or nest construction material. P. fuscatus colonies are 
initiated by one or more overwintered female gynes, which work 
together to raise the brood. Aggressive interactions result in the 
formation of a dominance hierarchy in which the most dominant 
individual is the egg-layer for the colony (Pardi, 1948). The domi- 
nant female must maintain a certain level of aggression in order to 
retain her dominant status, but her elevated rank is communicated 
by chemical cues originating in the head (Downing, 1982). Domi- 
nant wasps frequently chew on the head and thorax of their subor- 
dinates, and when threatening other females will lunge toward them 
with open mandibles. The ectal mandibular gland opening is 
exposed at these times, suggesting that it may be the source of 
chemical signals important for the communication of status during 
aggressive interactions. 
Acknowledgements 
We would like to thank D. Post and B. J. Harrington for provid- 
ing useful criticisms on early drafts of this manuscript. The research 
