1983] 
Root & Messina — Exenia canadensis 
15 
Six of 22 pupae that were collected on August 21, 1979, were 
parasitized by Spilochaleis albifrons (Walsh) (Chalcidae), a species 
that has previously been reported from Exenia dispar Lacordaire 
(Burks 1979). One chalcid emerged from each host. No S. albifrons 
were found in E. canadensis that were collected as larvae. If this 
chalcid attacks only pupae, it must be able to oviposit through the 
case wall because the case rim is sealed to the substrate by the 
prepupae. In this regard, it is interesting to note that S. albifrons has 
been taken from a broad range of unrelated case-bearing and leaf- 
mining insects. Moreover, at least four of the seven species in the 
side group, to which S. albifrons belongs, parasitize case-bearing 
chlamisines and coleophorids (Burks 1979). These observations 
suggest that the evolution of specializations in Spilochaleis is more 
closely linked to the abilities required to penetrate materials that 
cover the host than it is to factors that are more narrowly associated 
with the host’s taxonomic affinity. 
Larval mermithid nematodes were found in dissections of a few 
field collected E. canadensis larvae. These parasites are functionally 
similar to parasitoids, killing the hosts as they exit the body follow- 
ing development (Nickle 1974). 
Larvae of an erythraeid mite, Leptus sp., were found attached at 
several locations on beetles. In a survey done in late August 1979, 
67% of the 43 adult beetles sampled bore at least one mite. There 
was an average of 1.7 mites on the infested beetles and as many as 
five mites were found on a single host. Nothing is known about the 
influence of these mites on the beetles. 
Table 3: Per cent of E. canadensis larvae parasitized by a Tetrastichus sp. in 1979 
and 1980. (Sample sizes in parentheses.) 
Site 
Collection date 
Brooktondale 1979 
3 July 
29 July 
21 August 
21 August' 
17(107) 
16(57) 
38(21) 
27(22)^ 
Whipple Farm 1980 
28 June 
1 July 
4 July 
16 July 
23(61) 
42(19) 
40(55) 
31(13) 
'These cases contained pupae; the larvae had cemented the case rim to the substrate 
prior to collection. 
-An additional 27% of the pupae were parasitized by Spilochaleis albifrons. 
