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Psyche 
[March 
nitrogen levels should develop at a faster rate and gain more larval 
biomass. A highly significant difference (P < 0.05) exists in the 
nitrogen content between cultivated and weedy umbellifer species 
(Table 1). In terms of larval growth rates, a significant correlation 
exists between the weight gained per day and the nitrogen content 
of the plant (r = .701, 30 df.). Cultivated umbellifer species con- 
tain approximately 1% more total nitrogen than weedy umbellifer 
species, which in terms of protein content means an increase of ap- 
proximately 6.25% (Lord 1968). This increase in nitrogen protein 
content would allow larvae to gain more weight per unit of food, 
thus utilizing their ingested food more efficiently. 
The differential growth rates displayed by larvae reared on culti- 
vated and weedy umbellifer species is most likely due to a variety 
of factors. Cultivated umbellifer species generally appear to be more 
digestible and more nutritionally adequate for larvae of P. polyxenes. 
Is it possible that through the long history of the domestication and 
cultivation of plants that man has developed plants more digestible 
and nutritionally adequate for insects as well as for himself? Organ- 
isms have a limited amount of energy to spend and will be selected 
to partition this energy in different ways depending upon changing 
environments and physiological conditions (Cody 1966). Any activity 
of an organism, or more precisely, the energy expenditure for that 
activity, can be viewed only in relation to all other demands for 
energy. Wild or weedy umbellifer species are under a constant selec- 
tion pressure, always adapting to new predators, be they arthropod, 
vertebrate, or pathogen. Domesticated and cultivated species have 
been carefully and artificially selected for increased palatibility, yield, 
and nutritional quantities possibly at the expense of the plant’s own 
defenses. Thus, in producing plants more edible and nutritionally 
adequate for man, agriculturists have unintentionally made these 
plants more edible and nutritionally adequate for the insect herbi- 
vore. Has man, in a sense, chained himself to the plant, having to 
provide for the plant’s defense through the use of insecticides or 
through other biological control mechanisms? 
Acknowledgements 
This research was in part supported by Hatch Grant # 1394 13 
to Dr. Paul P. Feeny. Dr. Dennis Parnell added a variety of useful 
comments on the manuscript. 
