Sweetclover weevil

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Family: Curculinionidae
Species: Sitona cylindricollis
Common names: sweetclover weevil
Hosts: alfalfa, clover

Agriculture and agri-food canada insect identification no. 65 march 1981

sweetclover weevil

Sitona cylindricollis (fahraeus)

the sweetclover weevil, native to central europe, was first introduced into canada in 1924. It has since spread from the atlantic to the rockies, with infestation most severe in the prairie provinces. Injury:

in addition to sweetclover, this weevil also attacks alfalfa. The adult feeds on the foliage of host plants in the spring and fall. Crescent-shaped pieces are eaten out of the leaves. when infestation is severe, entire leaves except for the mid-stem may be consumed, and the outer bark of stems damaged. Larvae feed on the roots of host plants during the summer, but cause little damage.

Life history:

sweetclover weevils overwinter as adults in the soil or under plant debris. They emerge from the middle of April to the middle of may. Adults are 4 mm long, dark grey with yellow and dark patches, with short blunt snouts. Eggs are deposited on the soil surface from may until August. A single female may lay up to 1600 eggs. These hatch within 2-3 weeks. The newly emerged larvae burrow to a depth of 15 cm into the soil to feed on host roots. Larvae are grey-white, legless and reach a length of 4 mm. Late in july the larvae work their way upwards to pupate in the top 5 to 8 cm of soil. Adults appear in early August and
feed on host plants until the onset of cold weather. There is a single generation per year.

Pest management:

crop rotation is of some benefit in reducing losses from the sweetclover weevil. If chemical controls are necessary, contact your provincial department of agriculture for those best suited.