1982] Reed & Akre — Vespula austraiea and V. aeadiea 193 
V austriaea forcibly invades a host colony after worker emergence 
and does not coexist with the host queen (Reed 1982). Thus, the 
secretion of the Dufour’s gland does not appear to act as a pacifying 
agent in V austriaea parasitism, and may function as an alarm or 
dispersing chemical (Reed 1982). The possibility of differing func- 
tions of this gland is indicated by the condition of the gland in the 
two species prior to usurpation. In freshly dissected, preusurpation 
D. arctica parasites the gland was clearly empty, whereas in preus- 
urpation V austriaea females the gland was filled with a clear oil 
substance. A similar relationship between an enlarged Dufour’s 
gland and social parasitism is found among the slave-making ants of 
the subfamily Formicinae (Parry and Morgan 1979, Regnier and 
Wilson 1971) and the dulotic ant Harpagoxenus canadensis M. R. 
Smith (Buschinger and Alloway 1978). In some of these slave- 
makers the gland discharges a chemical that disperses the defending 
host workers and attracts other slave-making workers (Regnier and 
Wilson 1971). 
In conclusion, V austriaea possesses morphological features 
significantly different from the host species. Some, such as the pow- 
erful mandibles and front legs, and large curved sting, function as 
important offensive weapons during colony invasion. Other charac- 
teristics, such as the large gastral retractor muscles that enable the 
parasite to tightly hold the sclerites together, serve as an important 
defense against stinging host workers. The function of the large 
Dufour’s gland in vespine inquilines remains obscure; however, it 
probably plays a key role in usurpation and control of the host 
colony. 
Acknowledgements 
Appreciation is extended to the following institutions and 
researchers for generously supplying specimens for the morpho- 
metric study: American Museum of Natural History (M. Favreau); 
California Academy of Sciences (P. H. Arnaud); Florida State Col- 
lection of Arthropods (W. V. Weems); Museum of Comparative 
Zoology, Harvard (S. M. Foster); Oregon State University (G. Fer- 
guson); University of Alberta (D. Shpeley); University of British 
Columbians. G. Cannings); University of California-Davis (L. S. 
Kimsey); and University of Minnesota (P. Clausen). 
