Integrated Pest Management of Pea Leaf Weevil in North Dakota

Photo Credit:

H. Goulet, retired, Agriculture and Agri-Food, Canada, Ottawa

Pea leaf weevil

Pea leaf weevil (PLW), Sitona lineatus Linnaeus, (Coleoptera: Curculionidae) is an invasive insect pest that first was detected in southwestern North Dakota on field peas in Golden Valley County during the fall of 2016. Pea leaf weevil is a significant insect pest of field peas and faba beans, and can reduce yields severely.

Pea leaf weevil infests cultivated and wild legume species, including field peas, faba beans, alfalfa and dry beans. However, economic damage only occurs on field peas and faba beans. Clover and alfalfa serve as secondary hosts, but larvae do not develop fully on these crops. Pea leaf weevil also feeds on foliage of dry bean, lentils, lupins and vetch, but does not cause economic damage. Chickpeas are not known to be a host of PLW.

Field peas

Pea leaf weevil, native to Europe and North Africa, was first reported in North America during the 1920s. Since then, it has become an established pest in parts of Florida, Virginia, Texas, the Pacific Northwest (Idaho, Washington), Montana and Canada (British Columbia, Alberta and Saskatchewan).

In the last decade, PLW populations have been moving eastward, affecting increased field pea acreage. Pea leaf weevil is a common insect pest where field peas or faba beans are grown in western North Dakota. It is most prevalent in the southwest (Dunn, Golden Valley and Stark counties), north-central (Mountrail and Ward counties) and northwest (Divide County).

Egg (Figure 1) – Small and white when laid; gradually turn black before hatching

Photo Credit:

M. Dolinski, Canada

Figure 1. Adult pea leaf weevil and eggs on soil.

Larva (Figure 2) – Legless and white, with a dark brown head capsule; range from ⅛ to ¼ inch long; curls into a C-shape when disturbed

Photo Credit:

M. Dolinski, Canada

Figure 2. Larva of pea leaf weevil.

Pupa (Figure 3) – Resting stage

Figure 3. Pupa of pea leaf weevil

Adult (Figure 4) – Adult weevils are about 3/16 inch long, slender and grayish brown with a broad snout PLW is similar in appearance to the sweet clover weevil (Sitona cylindricollis Fåhraeus) (Figure 5) and other Sitona weevils. Adult PLW can be separated by the appearance of three light stripes on the thorax that extend to the wing covers on young adults. An experienced entomologist can assist in making a positive identification.

Photo Credit:

Natasha Wright, Cook's Pest Control, www.bugwood.org

Figure 4. Adult pea leaf weevil

Photo Credit:

Pest and Diseases Image Library, www.bugwood.org

Figure 5. Adult sweet clover weevil.

Adult PLW will overwinter in alfalfa and other perennial legumes, roadside ditches and shelterbelts. Adults will emerge in the spring as temperatures rise above 55 to 63 F and begin flying into spring-seeded field peas or faba beans. Adult PLW feed on leaves, causing a half moon, notched appearance along the leaf margins.

Adults mate and females lay eggs singly near the soil surface near developing host plants from May to June. Each female can lay between 1,000 to a maximum of 3,299 eggs in field peas.

After two to three weeks, eggs will hatch. Newly hatched larvae burrow into the soil to find and feed on nitrogen-fixing root nodules of its host plant. Larvae will develop through five instar stages in four to eight weeks.

Mature larva pupate in the soil. The pupal stage is a nonfeeding developmental stage without plant damage. The new generation of adults emerge during late July and into August. Adults will search out pulse or related forage crops and feed on the vegetation before seeking overwintering sites in late fall.

Adults feed on the early clam leaves, causing a symmetrical pattern of half-moon notches (Figure 6). Leaf feeding by adults typically does not result in yield loss because the crop usually compensates and recovers.

Photo Credit:

P. Beauzay, NDSU

Figure 6. Leaf-feeding notches from adult.

However, larva feed on the nitrogen-fixing bacteria within root nodules, causing significant damage to nodules (Figure 7). This damage also reduces soil- and plantavailable nitrogen for the current and future crops, which results in poor plant growth and lower crop yields.

Photo Credit:

P. Beauzay, NDSU

Figure 7. Larva feeding on nitrogen-fixing bacteria within root nodules.

Scouting should occur when crops have just emerged in the spring (Figure 8), especially when PLW populations are high. Look for the halfmoon leaf notches on the lowest leaves of the plant along field edges first (Figure 6).

To establish an average number of plants with leaf notches, scout fields and sample 10 seedlings per 10 sampling sites in the field: five sampling sites near the field edge and five sampling sites about 35 yards into the field (Figure 8). Space sampling sites in fields about 25 yards apart. Later in the growing season (late June and July) during flowering, dig up plants and examine root nodules for larvae or feeding injury (Figure 9) using a hand-held 10x lens.

Figure 8. Scouting for leaf feeding injury from pea leaf weevils in field peas

Photo Credit:

P. Beauzay, NDSU

Figure 9. Larva of pea leaf weevil excised from root nodule.

During the summer, scout for newly emerged adult PLW in late July. Adult weevils are difficult to scout for because they can drop readily to the soil surface and are cryptic.

As pea harvest begins, adult PLW will migrate out of the field to feed on nearby legumes, such as alfalfa and sweet clover. These secondary hosts may harbor other weevils, such as the sweet clover weevil (Figure 5), that look similar to PLW.