240 
Psyche 
[September 
Table 4. Length of pupation, fecundity and fertility of monarch butterflies 
raised on various plants of the genus Asclepias. 
Host plant 
Number of 
animals 
Mean length 
of pupation 
(days) 
Mean total 
number of eggs 
per female 
± SE 12 
Mean percent 
of eggs 
hatching 
± SE 13 
A. curassavica 
12 
10.31 
105.7 ± 8.7 
91.6 ± 4.9 
A. syria ca 
17 
10.67 
117.2 ± 10.6 
89.1 ± 5.7 
A. incarnata 
12 
11.02 
110.3 ± 9.4 
87.3 ± 6.3 
A. tuberosa 
9 
10.57 
106.0 ± 9.6 
93.2 ± 4.8 
T.os (df 3,20) = 3.10 
F.oi (df 3,20) =4.94 
2 F = 1.13 
3 F = 0.73 
concentrations ( Duffey 1970, Singh and Rastogi 1970) and only 
marginally toxic (Hansen 1924, Heal et al. 1950). It is found, 
however, that contrary to expected results, larvae reared on the 
highly toxic A. curcissavica gained more biomass per day, spent the 
shortest time in the 4th instar, and were the most efficient at utilizing 
and converting digested matter into biomass (Table 2). In addition, 
larvae reared on A. curassavica utilized approximately 65% of the 
assimilated energy to produce biomass whereas only 32% of the 
assimilated energy was allocated to biomass for larvae reared on 
A. tuberosa (Table 3), and larvae reared on A. curassavica had the 
lowest ‘Respiratory Coefficient’ at 0.53 compared to larvae reared on 
A. tuberosa which had a value of 2.16. This means that larvae 
reared on the A. curassavica host plant were allocating about 2 
calories for biomass for every calorie lost through respiration and 
maintenance, w J hereas larvae reared on A. tuberosa allocated ap- 
proximately 0.5 calorie to biomass for every calorie lost through 
respiration and maintenance. It thus appears that there is little 
measurable ‘cost’ to detoxify or incorporate caridac glycosides by 
monarch larvae since the larvae grew and developed most rapidly 
on the most toxic Asclepias food plant tested. 
