The effects of sweetclover species, cultivars, and nitrate fertilizer on feeding by the sweetclover weevil, Sitona cylindricollis Fahraeus (Coleoptera: Curculionidae)

Sweetclover, Melilotus Miller, was planted in a field near Saskatoon, Saskatchewan, to determine the effects of species and cultivars on early season feeding by the sweetclover weevil, Sitona cylindricollis. The wild annual species M, infesta Cuss. was consumed less than were cultivars of M. alba (Desr.), which were generally consumed less than cultivars of M. officinalis (L.). The amount of feeding injury by the weevil among nine sweetclover entries was not significantly correlated with nitrate levels in cotyledons, unifoliolate, or first trifoliolate leaves. Weevils fed equally well On entries with high and low coumarin levels. Results from greenhouse cultivar trials generally paralleled those from the field. In an experiment in which different levels of ammonium nitrate fertilizer were broadcast prior to seeding of M. officinalis cultivar Norgold, levels of nitrate ion in the foliage were significantly correlated with fertilizer regime, but not with damage indices of the weevil. These experiments suggest that the nitrate ion in isolation is not the principal factor in the deterrence to sweetclover weevil feeding in M, infesta, and that elevating nitrate levels in sweetclover leaves would not confer resistance to this insect.