Pea leaf weevil (Sitona lineatus)
Biology and life history: Adult pea leaf weevils are small (about 1/5 in), elongate beetles with brown body and subtle, light grey stripes running lengthwise. Adults are dormant or with minimal activity and feeding during the winter, preferring alfalfa fields or field margins with other perennial legumes. In spring, they fly to pea fields where mating occurs. Females lay over 1,000 eggs in the soil or on plants. The grub-like larvae burrow down to root nodules where they feed. Adults emerge in late July to late August and feed on pulse crops until winter. There is one generation per year.
Host plants and crop damage: Adults feed on many species in the pea family, including alfalfa, lentils, beans, and others, but larvae prefer faba beans and garden pea. Larvae feeding on root nodules disrupt nitrogen fixation, leading to potentially significant damage. Adult feeding results in characteristic U-shaped notches along the leaf margins. Heavy infestations may lead to complete defoliation.
Management: Damage from pea leaf weevil can be prevented with good growing conditions; fields with high soil nitrogen and vigorous plant growth are generally not as severely affected. Biological control with Beauveria bassiana (fungus) and entomopathogenic nematodes showed promise in laboratory and field studies. Broad-spectrum insecticides should be considered as last resort. Although seed treatment appears to be as effective as foliar application it may be unnecessary in years with low infestation levels.