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166 P. Harris
Table 43
in East Austria with 3-5 larvae per plant. Some field mortality was noted: at one site on
E. cyparissias, 31 % ofthe eggs failed to hatch although they developed embryos and 9%
of the larvae died in the early instars. The population in part seems to be controlled by
oviposition behaviour as multiple oviposition into a stem is rare and when it does occur
only one larva survives to enter the root. In choice tests O. erythrocephala attacked
Canadian leafy spurge more often than E. esula, but there was no indication that
association with a particular spurge species in the field had formed a host race.
(b) Releases
Authority to release O. erythroceplwla was obtained in October 1979. The stock was
field collected as beetles in Switzerland on E. segllierana and E. cyparissias, and in
Austria on E. cyparissias and E. eSllla (Table 43). The sexes were separated on
collection and then released together at the release site in Canada later.
Open releases and recoveries of Oberea erythrocephala (Schr.) on E. esula-virgala complex
in Canada.
Release Date No. and Stage Source Release Site Recovery
15 Oct 79 30 larvae Switzerland Caronport, Saskatchewan 1 of 12 alive
May 80
27 Jun 80 70 males Switzerland Caronport, Saskatchewan 15 larvae Sep 80
60 females 31 larvae Sep 81
3 Jul80 70 males Switzerland Cardston. Alberta 17 larvae Sep 80
53 females o larvae Aug 81
14 Jul 80 49 males Switzerland Jameson, Saskatchewan 1 larva Sep 80
57 females o larvae Aug 81
26 Jun 81 55 males Switzerland Weyburn, Saskatchewan 14 larvae Aug 81
(8 on plants
attacked in lab)
30 Jun 81 59 males Switzerland Lauder, Manitoba 12 larvae Aug 81
36 females
10 Jul 81 90 adults Switzerland Manitou Lake, Saskatchewan 13 larvae Aug 81
& Austria
5 Aug 81 17 larvae Austria Caronport, Saskatchewan
In 1979,30 leafy spurge plants that had been attacked in the laboratory were transplanted
in mid-October to a spurge stand in Saskatchewan (Table 43) to check on
the ability of the larvae to survive the winter. The plants did not have time to establish
themselves before winter and some were killed. In the following May one larva was
found in 12 crowns examined and subsequently some oviposition girdling was found at
the site but no eggs or larvae.
Field collected beetles were released on three spurge stands in 1980 (Table 43) and
during the summer, stems with oviposition scars were tagged and then harvested in
September to determine the number of larvae that had tunnelled into the roots before
winter (Table 44).
The Cardston site was extremely fertile and the spurge so tall and dense that many
stems with oviposition scars were certainly missed but it had by far the best ratio of
oviposition scars to larvae. Unfortunately the site was burnt just before winter and in the
following June the spurge was sprayed with pic\oram. Thus it was hardly surprising that
no sign of the beetle was found in August 1981. In contrast at Caronport winter survival