The spring emergence biology of Ceutorhynchus obstrictus (Marsham) was investigated in 2003 and 2004 in relation to habitat type, vegetative cover, and soil temperature in the Mixed Grassland Ecoregion of western Canada. Although total emergence extended over 10–12 wk, emergence patterns were very similar in both years with limited emergence occurring for several weeks before and after a large emergence peak of comparatively short duration. In 2003, peak emergence occurred during a 3-wk period from 28 May to 13 June when 97.6% of C. obstrictus were collected; and in 2004, emergence of 55.6% of weevils occurred during the 1-wk period before 4 June. Peak emergence occurred as mean ground temperature (5 cm in depth) reached 15°C. The greatest number of weevils recorded from a single 1-m2 emergence trap was 956. Significantly more weevils emerged from sheltered and intermediately sheltered locations than from open grassy habitats; sheltered areas were predominantly shelterbelts and yard sites of caragana and poplar trees. No weevils emerged from 14 of 106 cages, and all cages were in open grassy habitat. Spring emergence of weevils in open grassy areas occurred slightly before those in sheltered and intermediately sheltered areas. Cages in open grassy habitat had the highest mean temperature as well as the highest maximum and lowest minimum temperatures in each sampling period. Significantly more males than females emerged early in the season, although during peak emergence there was no difference in sex ratio; and after peak emergence, significantly more females than males emerged.
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Vol. 99 • No. 1