1975] 
Erickson — Papilio polyxenes 
25 
assimilated through the gut wall, there is no further effect on its 
utilization, which supports the supposition of interference with di- 
gestion occurring in the gut of the larvae reared on weedy umbellifer 
species. 
Besides the apparent interference with digestion found in larvae 
reared on wild or weedy umbellifer species, are there any nutritional 
differences between the cultivated and wild plant species that may 
influence overall food utilization? Among the 32 umbellifer species 
tested, no significant difference was found in the caloric content of 
the leaf material offered to the larvae (Table 1). Thus, in terms 
of calories all leaves presented to the larvae were of equal value. 
It has been suggested that the water content of the host plant 
would greatly affect the utilization efficiencies. A strong significant 
difference (P < 0.0 1 ) exists between cultivated and weedy umbel- 
lifer species, with the cultivated species being much higher in water 
content than the weedy species. A definite negative correlation exists 
between plant dry matter content and the amount of larval weight 
gained (r = .466, 30 df.) and plant dry matter content and the 
utilization of ingested matter (r = .71 1 , 30 df.) . It has been shown 
in this laboratory, that by varying the water content of leaf material, 
the utilization of food by the cecropia moth, Hyalophora cecropia, 
is greatly affected (J. M. Scriber, in preparation). This effect 
was shown in lengthened development times for larvae reared on 
plants with low water content in which the total food consumed 
increased but the consumption rate remained relatively constant. In 
our experiment however, larval developmental times as well as total 
food consumed did not vary significantly but larval food utilization 
was affected by the digestibility and the efficiency of conversion of 
ingested food into larval biomass. It appears from the correlations 
found that the dry matter content of the umbellifer leaves may have 
some influence on the larval utilization efficiences to an unknown 
degree. 
The importance of nitrogen for larval growth and development 
cannot be overemphasized. Friend (1958), House (1961, 1962), 
and Dadd (1973) have discussed the qualitative requirements of 
proteins and amino acids for larval development. There appears to 
be an optimal nitrogen level, which varies from species to species, 
that produces maximal larval growth (Dadd 1961, House 1959, 
Vanderzant 1958). If nitrogen is a limiting factor for larval growth 
in this species as has been shown for other lepidopterous larvae 
(Erickson 1972), larvae reared on plant species containing higher 
