1980] 
Post & Jeanne — Sternal Glands of Polistes 
55 
close packed and polygonal and bounded by a membrane. The 
discrepancy may be an artifact of the techniques used in each study. 
Hermann and Dirks (1974) sectioned fixed and embedded material, 
as we did, while Landolt and Akre (1979) dissected fixed specimens. 
It is possible that during dissection they may have ruptured the 
membrane enclosing the gland cells, allowing them to float free at the 
ends of their ducts and assume a spheroid form. On the other hand, it 
is possible that the difference is taxonomic. We have found that the 
class 3 cells on the fifth sternite of females of Polybia (Polistinae: 
Polybiini) are globose and apparently not bounded by a membrane, 
even in histological sections (Jeanne and Post, in preparation). It is 
not clear whether Landolt and Akre meant to generalize their 
statement to all genera they studied ( Vespula, Dolichovespula, 
Vespa, Polistes, and Mischocyttarus) or just to Vespula and Doli¬ 
chovespula. 
If the columnar epithelial cells associated with the ducted class 3 
cells on the sixth sternite are indeed producing an exocrine secretion, 
it is not clear what its function could be. Even though this secretion 
would reach the cuticular surface to the side of the brush, it could well 
be applied to the nest petiole along with the product of the class 3 
cells. Whether there it serves as a component of the ant repellent or 
has some other function is unknown. Alternatively, if it is volatile, it 
could evaporate from the cuticular surface, in which case its function 
is less likely to be involved with defense against ants. 
The fact that P. canadensis has approximately three times as many 
class 3 cells on sternite 6 as does P. fuscatus is consistent with the 
hypothesis that these cells produce the ant repellent that is applied to 
the nest petiole. Since ant predation pressure is higher in the tropics 
than temperate regions (Jeanne, 1979), one way P. canadensis, a 
tropical species, could counter this increased threat is by having more 
gland cells, producing greater amounts of ant repellent secretion. 
Turillazzi (1979) also found that P. gallicus, a species ranging into 
•northerp Europe, has fewer class 3 gland cells than does either P. 
omissus (Weyrauch) or P.foederatus, species of southern Europe and 
Africa (Kemper & Dohring, 1967). This correlation between gland 
size and geographic distribution need not, of course, rule out other 
hypotheses as to the function of the secretion. 
The role of the class 3 gland cells on sternite 5 is open to question. It 
is possible that the secretion has the same function as that of the 6th 
sternal gland, for, as Turillazzi (1979) points out, it would also be 
