Legume Seedling Feeding Preferences of Adult Sitona hispidulus (F.) (Coleoptera: Curculionidae)

A greenhouse experiment was designed to evaluate a series of forage legume seedlings in the cotyledon stage for susceptibility to seeding damage from adult Sitona hispidulus (F.). Seedlings of a range of cultivars of white clover, Trifolium repens; alfalfa, Medicago sativa; red clover, Trifolium pratense; Lotus spp.; and crown vetch, Coronilla varia, were transplanted in the cotyledon stage into trays in a complete randomized block design. Adult weevils were added at a rate of one weevil per seedling. Feeding preferences of the weevils were assessed by visually estimating percentage defoliation of the seedlings 3 and 6–7 d later. A further experiment using cotyledon leaf discs randomly threaded onto an entomological pin further investigated weevil feeding preferences. Two similar whole seedling experiments and the leaf disc experiment indicated that white clover ‘Ladino’ was the most preferred species of the legume seedlings offered, followed by alfalfa ‘WL 318’ and two red clover cultivars, ‘Kura’ and ‘Arlington’. Lotus spp. and crown vetch were preferred least. Defoliation levels ranged from 32 to 93% after 6 to 7 d in the whole seedling experiments and from 11 to 46% after 4h in the leaf-disc experiment. Damage assessments of the unifoliate or first true leaflets indicated an order of feeding preference similar to that found for cotyledon leaves. Defoliation levels of whole seedlings were not linearly correlated with seedling size or fresh weight, and this, supported by the results with the leaf discs, suggest that in the whole seedling experiments, plant size did not determine the levels of defoliation.