MORPHOLOGICAL COMPARISONS BETWEEN THE 
OBLIGATE SOCIAL PARASITE, VESPULA AUSTRIACA 
(PANZER), AND ITS HOST, VESPULA ACADICA (SLADEN) 
(HYMENOPTERA: VESPIDAE)' 
By 
Hal C. Reed and Roger D. Akre * 2 
Department of Entomology 
Washington State University 
Pullman, WA 99164 
Introduction 
Obligate social parasites (inquilines) show a vast array of be- 
havioral and morphological adaptations to their unique mode of life 
(Wilson 1971). The hazards of colony invasion, usurpation, and 
subsequent subjugation of members of the host colony (queen 
and/or workers) require special features in order to overcome col- 
ony defenses and to become integrated within the host’s society. Not 
only do these species have adaptations for colony takeover, but they 
also lack certain social characteristics, the most notable being the 
absence of a worker caste. 
Such traits are exemplified in the workerless ant inquiline, Tel- 
eutomyrmex sehneideri Kutter, that has enlarged tarsal claws and a 
gaster with a concave venter which enables this parasite to ride on 
the dorsum of its host (Wilson 1971). Among the parasitic bumble 
bees ( Psithvrus spp.) a number of characteristics, such as strong 
development of the sting and exoskeleton, are adapted for success- 
ful colony takeover, while other social traits, such as a pollen- 
collecting apparatus on the hind leg, are lacking (Alford 1975). 
Similarly, vespine inquilines are distinct from their hosts in possess- 
ing stronger exoskeletons, a closer fitting of their abdominal seg- 
ments, stouter and more recurved stings, broader heads, more 
powerfully built mandibles, and sharp bidentate clypei (Weyrauch 
'Scientific Paper Number 6233, Washington State University, College of Agriculture 
Research Center, Pullman. Work done under Project 0037. 
2 Research Assistant and Entomologist, respectively. Department of Entomology, 
Washington State University, Pullman 99164. 
Manuscript received by the editor May 10, 1982. 
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