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142 D. P. Pcschken
Lema cyanella
(L.) (Coleoptera:
Chrysomelidae)
larvae contained Nosema spores and 1.3% were parasitized by an as yet unidentified
hymenopterous parasite. In Saskatchewan and Alberta, the mortality was higher: 35%
of a total of 402 larvae collected in the spring of 1975, 1976, and 1977 was dead.
Comparing only those thistles that emerged during the oviposition period of the fly,
shoots with galls on the main shoot were 57% shorter, and those with sideshoot galls
were 10% shorter than ungalled shoots in Quebec when growing on an uncultivated site
with competing vegetation. However, in Saskatchewan even an average of 13 galls per
shoot did not reduce the height, dry weight, number of seed heads or the dry weight of
new shoots produced by thistles growing in the absence of competition on heavy fertile
soil with sufficient moisture (Peschken et al. 1982).
(a) Ecology
This leaf-feeder is widely distributed in Europe and A!>ia between latitudes 35°N and
65°N and occurs about three-quarters of the range of C. arvense (Peschken & Johnson
1979). It is rare in Germany, Austria, Czechoslovakia, and Poland and is more frequent
in western Europe (Zwolfer & Pattullo 1970, Winiarska 1973). Collection records
indicate that moist habitats are preferred (Winiarska 1973, ZwOlfer & Pattullo 1970,
Lopatin 1960, Peschken unpublished).
The adult beetles hibernate and in Europe they appear on the thistle rosettes at about
the end of April. They oviposit in May and the new generation of adults can be observed
from the end of June until August. There is one generation per year.
(b) Host specificity
The only confirmed breeding host in Europe is C. arvense (Zwolfer & Pattulo 1970,
Peschken & Johnson 1979). In the screening tests for host specificity, it did not feed on
any cultivated plants but on several Cirsium spp. native to North America (Peschken &
Johnson 1979). One of these, Cirsium drummondiiT. & G., was even preferred in favour
of Canada thistle in choice tests in the laboratory. In a field cage, however, the females
laid most eggs on those thistles which were most prevalent in terms of biomass of leaves
and stems (Peschken unpublished).
(c) Releases
The releases listed on Table 33 were made for the purpose of testing the host preference
of L. cyanella in the more natural environment of a field cage, not for establishment in
the field. In the course of these field cage studies, 4 out of 28 beetles survived the 1978n9
winter. In subsequent years the beetles were collected in the fall and overwintered in the
laboratory. However, another adult was collected in the field in the spring of 1981. Thus
L. cyan ella can survive the winter in Saskatchewan. No larvae were found in 1981. The
release of L. cyanella with the intent of establishment has not yet been approved out of
concern for the Cirsium species of our native North American flora.