74 
Psyche 
[Vol. 90 
Table 2: Consumption of exposed and encased larvae of E. canadensis by three 
arthropod predators in laboratory arenas. 
% available prey consumed 
Predator 
Exposed 
Encased 
N' 
P^ 
Podisus niaculiventris 
69 
19 
54 
.001 
nymphs 
Nahicula subcoleoptrata 
70 
7 
30 
.001 
adults 
Hippodamia glacialis 
87 
0 
30 
.001 
'Number of each prey type offered. 
-Chi-square test, where expected values assume equal consumption of each prey type. 
in the case of a larva that had cemented the opening to the substrate 
before it died. We could not determine if Tetrastichus females ovi- 
posit through the case wall or under the rim. In the field, however, we 
commonly observed Tetrastichus adults that remained perched on 
the side of a larval case for prolonged periods. Perhaps these wasps 
were waiting for the larva to move and thus expose a vulnerable 
spot for oviposition. 
^ N. subcoleoptrata H. glacialis 
Hours after release 
Predator starvation ;• 24,° 48, ° 72 h 
Fig. 1 1: Consumption of exposed E. canadensis larvae by Nahicula subcoleoptrata 
and Hippodamia glacialis in the laboratory. Predators were starved for 24-72 h 
before release. Ten prey were offered per trial. 
