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[Vol. 90 
new areas of the world when introduced by man, and (4) tendency 
for workers to become scavengers on carrion or human food and 
refuse in the late summer. The common possession of these derived 
features supports a monophyletic origin of this group within the 
Vespinae. The interaction of these same features accounts for the 
greater public health importance of these species relative to other 
vespines. 
The vespid subfamilies Polistinae and Vespinae, comprised exclu- 
sively of eusocial species, are thought to have evolved from a com- 
mon social ancestor (Carpenter, 1982). The Polistinae are diverse in 
their methods of colony founding and number of functional repro- 
ductives (Iwata, 1976; Jeanne, 1980); their social behavior appears 
loosely associated with a tropical or temperate existence. In con- 
trast, all vespines are characteristically haplometrotic and mo- 
nogynous, and form annual colonies (thought to be temperate 
adaptations), regardless of their distribution (Iwata, 1976; van der 
Vecht, 1957; Akre et al., 1980). Thus, the characteristic social organ- 
ization of the Vespinae appears to be the expression of a common 
ancestral trait, rather than an immediate response to ecological 
conditions. This interpretation suggests that the Vespinae may have 
originated in temperate regions rather than in the tropics (Carpen- 
ter, 1982), as has been previously assumed. 
The evolution of eusociality in vespids is thought to have 
occurred by one of two general routes: (1) the subsocial or matri- 
filial monogynous route in which prolonged maternal care provides 
opportunities for social interaction between a foundress and her 
offspring (Evans & West Eberhard, 1970; Spradbery, 1973a), or (2) 
the polygynous or parasocial route in which nesting associations of 
foundresses of the same generation lead to increasingly complex 
levels of social organization (Lin & Michener, 1972; West Eberhard, 
1978). Insofar as the occurrence of occasional polygyny in the Ves- 
pinae bears on the social origins of this group, the recurrent ability 
of colonies to tolerate multiple functional reproductives strengthens 
an argument for the evolution of eusociality via the parasocial route 
in the Polistinae + Vespinae. The occurrence of perennial, polygy- 
nous colonies of Vespula may be viewed as a reversion to a more 
primitive behavioral and physiological mode. Further investigations 
of this phenomenon should aid in elucidating the environmental and 
social contexts under which it occurs. 
