Seasonal Changes in Daily Activity Periods of the Sweetclover Weevil12

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Abstract
Daily activity of adult sweetclover weevils, Sitona cylindricollis Fåhraeus, was determined throughout 3 consecutive growing seasons at Lincoln, Nebraska. In 2 of the 3 years adults were found most frequently on early spring sweetclover foliage during the day. By mid July in all 3 years, weevils were most numerous on the foliage after dark and almost absent during daylight. In all years weevil activity was low in late summer; but by fall, more weevils were found on the plants at night though activity was not as restricted to this period as during July. The major influence on activity appeared to be light; the secondary influence was temperature. Activity seemed to be highest at night unless low temperatures caused the insects to shift their activity to the warmer daylight hours, which may explain the daylight activity in spring and fall, when nighttime temperatures tend to fall below the threshold for weevil activity.