pdf, 57.71Mb - Entomological Society of Canada

140 D. P. Peschken
Ceutorhynchus
lItura (F.)
(Coleoptera:
Curcullonidae)
of 15°C, development was not completed. while at 22.5°C to 25°C. it was completed in 33-
38 days. Thus high temperatures and humidities are needed for an optimal rate of
development. This agrees with the coastal Mediterranean and Atlantic native distribution
of the beetles (Peschken 1971).
(b) Releases
Releases up to and including 1968 were reported by Peschken (1971). The colony at
Lacombe, Alberta survived until 1971. In addition, 170 were released in 1969 at Fon
Vermilion, Albena (58°28' N), which is the most northern and coolest of all release sites
of A. carduorum in Canada (Table 33). In 1970, 1018 beetles were released at Essex,
Ontario (42° 22' N), which is the most southern and warmest of all release sites. Both
releases were made early in the spring which prevented overdispersal in high
temperatures (Peschken 1977). Predation of eggs and larvae was severe at Essex and less
severe at Fort Vermilion. In the fall of the respective release years, 18 adults were found
at Fon Vermilion and only one at Essex, although six times as many beetles had been
released at the latter site. At Essex, the carabid beetle Lebia viridis Say, was implicated as
a main predator of eggs and larvae. In feeding tests it consumed 0.7 eggs and larvae per
hour (Peschken 1971). No A. carduorum were found in subsequent years.
(a) Ecology
The ecology of this stem-mining weevil was summarized by Peschken (1971). Since then
Peschken & Beecher (1973) and Peschken & Wilkinson (1981) have published additional
information. The weevil larvae feed on the parenchyma tissue of the stem and avoid the
vascular bundles. In Canada, the females oviposit from early May until the beginning of
June. The new adults copulate and feed heavily during sunny, late summer and early fall
days ",ith temperatures over 18°C, but do not oviposit. At this time, males outnumber
females 2: 1.
In spring, females outnumber the males 1.6: 1. In the laboratory females laid an average
of 122 eggs in temperatures varying from 17°C to 27°C during a 16.5 hour day and 7°C to
17°C during a 7.5 hour night. An average of 80% of the eggs hatched.
(b) Releases
A total of 1188 weevils was released in five provinces at 11 release sites (Table 33).
The insect became established at nine sites in varying climates in four provinces of
Canada. It spread slowly, 2.9 km in 12 years in Ontario, 90 m and 75 m in six and four
years respectively at two release sites in Saskatchewan. The length of mines varied on
the different release sites from 5 to 23 cm. The short, 5 cm, mines were found at
Lacombe, Albena where almost all of the thistles were smooth-leaved, resembling
those of C. arvense var. integrifolium Wimm. & Grab. The weevil preferred dense
patches of thistle.
Mined shoots were from 1.09 to 1.96 times taller than unmined ones in the fall
(Peschken & Wilkinson 1981). This is explained as follows: early emerged, unattacked
thistle rosettes grow into taller shoots by fall than later emerged ones (Peschken &
Wilkinson 1981). The weevil oviposits into the early emerged rosettes and it is