1983] 
Root & Messina — Exenia canadensis 
73 
Figs. 9-10: Adult E. c anadensis. 9, Dorsal view. 10, Ventral view. Scale bars = 500 
/urn. 
even though they made repeated probes. In those instances when 
these hemipterans did consume encased prey, they fed through the 
case opening on the few occasions when a larva had been knocked 
on its side. This is an unlikely event in nature because dislodged 
larvae fall from the plant. The chewing predator, H. glacialis, 
attacked the encased larvae by attempting to insert the mandibles 
under the rim of the case; we never observed success in this 
endeavor. 
The case is an ineffective barrier to certain adapted paraSitoids. 
Larvae at both field sites were parasitized by a Tetrastichus sp. 
(Eulophidae); this was possibly T. chlamytis Ashmead, a species 
that is only known to attack chlamisine beetles (Burks 1979). Rates 
of parasitism ranged from 16 to 42% (Table 3). We obtained an 
average of 8.6 Tetrastichus adults/ infested host (range, 5-14 wasps; 
n = 37 hosts). Parasitoids emerged from larvae that were collected in 
the field as both early (I-Il) and late (III-IV) instars. The cuticle of a 
parasitized larva turns from white to black and the host dies shortly 
before the time it would normally pupate. The wasps usually 
emerged from the case opening, but a small exit hole was observed 
