|scientific name Sitona cylindricollis |
common name Sweet Clover Weevil
Forage crops where sweet clover, alsike clover, and alfalfa are grown (Davidson and Lyon 1979).
Migration extends over a three week period begining in late April (Campbell et al. 1989).
Body length ranges from 3.0 to 5.0 mm. Integument ranges from black to light brown, tibia, tarsi and antennae are generally reddish brown. Rostrum surface is flat, lower third slightly bisulcate. Median carnia is distinct, but weakly indicated, located between the apical concavities. Rostrum covered with recumbent and abundant brown and white scales, with intermixed brown setae that range from recumbent to slightly erect. Eyes are convex, described as moderately prominent. Pronotum is widest at the middle, evenly arcuate. Pronotal surface is smooth and shiny, with deeply impressed mid-sized and numerous punctures. Prosternal groove is intermediate between the fore-coxal cavities and the anterior of the prosternum. Elytra are broadly arcuate, strial punctures are small and weakly impressed. Each strial puncture bears a minute seta. Interstriae are 5 to 6 times wider than striae, are weakly convex, with finely punctured surfaces. Vestiture of elytra with many small, light brown to white scales that are recumbent and intermixed with numerous recumbent setae. (Adapted from Bright 1994, Bright and Bouchard 2008)
Adult sweet clover weevils may be identified from their close relatives by the elytral vestiture. The elytral vestiture consists of recumbent scales that are very abundant and interspersed by short recumbent setae. There are no erect scales or setae on the elytra. In the spring, the sweet clover weevil may be mistaken for the pea leaf weevil; overwintered pea leaf weevils are often without scales on the elytra and pronotum. The two can be distinguished by the distance between the coxa and a groove on the ventral surface of the pronotum. The distance between these two structures is non-existent in the pea leaf weevil. (Adapted from Bright 1994, Bright and Bouchard 2008).
Adult weevils that are sexually immature overwinter in the upper inch of soil, or on the soil surface beneath debris (Campbell et al. 1989). When temperatures rise in the spring, to mean temperatures of 15° C, emergence from overwintering habitats begins (Campbell et al. 1989). After emergence, weevils migrate from second-year clover fields to first year clover fields, via flight and walking. Migration, feeding and mating periods overlap, as mating begins after feeding begins and continues until weevils die (Davidson and Lyon 1979). Males are very aggressive in their search for mates (Herron 1953). Female weevils deposit eggs while feeding or at rest, with no active egg placement (Herron 1953, Campbell et al. 1989). Each female weevil produces between 1600 and 1800 eggs (Davidson and Lyon 1979, Campbell et al. 1989). Larvae consume root nodules of sweet clover, and pass through four instars before pupating in the soil (Herron 1953). In Ohio, larval development required 30 to 40 days, in Manitoba, development of the last two instars required 30 days (Herron 1953). Pupation in Ohio required 7 to 12 days (Herron 1953). New generation weevils begin emerging in mid summer, beginning in late June (Herron 1953). The timing of the life history of the weevil depends heavily on regional conditions, as the new generation does not emerge in Manitoba until late July (Herron 1953). Un-colonized seedlings are sought when the new generation emerges and are consumed (Campbell et al. 1989). Feeding activity continues until temperatures drop. Migration to new plants in summer and fall is achieved strictly via walking (Campbell et al. 1989). The sweet clover weevil is univoltine, completing one generation per year (Herron 1953, Hans 1961, Campbell et al.1989).
Abundance of this pest species is variable over time and space (Campbell et al. 1989).
Sitona cylindricollis larvae feed primarily upon Melilotus species (sweet clover) (Herron 1953, Campbell et al.1989). Adult weevils will feed upon Trifolium hybridium L. (alsike clover), Medicago lupulina L. (black medic) and Medicago sativa L. (alfalfa) in the absence of sweet clover (Herron 1953).
According to Bright and Bouchard (2008), the sweet clover weevil occurs in all Canadian provinces and territories, with the exception of Newfoundland and is expected to occur in all of the mainland States. The weevil occurs commonly in Europe and western Asia, and was likely introduced to North America from one of those continents (Campbell et al.1989, Bright and Bouchard 2008).
Adults are nocturnal feeders (Campbell et al.1989). Larval feeding on the roots is believed to vector root rot diseases (Campbell et al.1989). Adult feeding is characterized by crescent shaped notches along the leaf margins (Herron 1953, Bright and Bouchard 2008). Developing sweet clover seeds may be fed upon when foliage is unavailable (Campbell et al.1989). The sweet clover weevil is controlled by plowing under infested clover crops; the timing of the plowing is crucial, and can destroy up to 85% of eggs and new generation larvae (White 1983).
Hector Carcamo (2012-01-27)
Should also mention that this is a major pest of clovers and likely the reason why alfalfa is the main forage crop in Canada. Some have suggested using this species as a biocontrol of clovers in Alaska.
Felix Sperling (2012-01-28)
Hi Hector, Thanks for your comments. Could you please provide some exact wording on how the text should be revised, plus published references to back it up? Danny can then revise the page and list you as a reviser under Authorship, below Meghan Vankosky.
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