Tag: Sitona lineatus

PEAS AND FABA BEANS BEWARE: THE PEA LEAF WEEVIL IS OUT AND ABOUT

This week’s “Insect of the Week” is the Pea Leaf Weevil. Larval hosts are field peas and faba beans. Adults can spread to other cultivated and wild legumes, such as alfalfa, beans and lentils. Each adult female lays up to 300 eggs in one summer! The eggs hatch in the soil near developing plants and larvae move to feed on nitrogen-fixing nodules. This results in partial or complete inhibition of nitrogen fixation by the plant, causing poor plant growth. Adults feed on leaves and growing points of seedlings, causing notches in leaf margins.

Adult pea leaf weevil damage, showing crescent shaped notches on the leaf margin (AAFC)

The pea leaf weevil is a slender greyish-brown insect measuring approximately 5 mm in length. These insects can be distinguished by three light-coloured stripes extending length-wise down the thorax and sometimes the abdomen. All species of Sitona, including the pea leaf weevil, have a short snout. Mature larva grow up to 3.5-5.5 mm long, and are legless and c-shaped with a brown head.

Biological and monitoring information related to pea leaf weevil in field crops is posted by the province of Alberta and in the PPMN monitoring protocol. Also access the Pea leaf weevil page from the Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Management field guide. (en français : Guide d’identification des ravageurs des grandes cultures et des cultures fourragères et de leurs ennemis naturels et mesures de lutte applicables à l’Ouest canadien).

Pea leaf weevil

The pea leaf weevil is a slender greyish-brown insect measuring approximately 5 mm in length (Fig. 1, Left image). Pea leaf weevil resembles the sweet clover weevil (Sitona cylindricollis) but the former is distinguished by three light-coloured stripes extending length-wise down thorax and sometimes the abdomen. All species of Sitona, including the pea leaf weevil, have a short snout.

Adults will feed upon the leaf margins and growing points of legume seedlings (alfalfa, clover, dry beans, faba beans, peas) and produce a characteristic, scalloped (notched) edge (Fig. 2). Females lay their eggs in the soil either near or on developing pea or faba bean plants from May to June.

Figure 2. Examples of adult pea leaf weevil damage on field pea seedlings, (A) seedling with notches on all nodes, (B) stereotypical crescent shaped notches on the leaf margin, (C) clam or terminal leaf of the pea seedling with arrows indicating the feeding notches.
All photos courtesy of Dr. L. Dosdall.

Larvae develop under the soil and are “C” shaped and milky-white with a dark-brown head capsule ranging in length from 3.5-5.5 mm (Figure 3). Larvae develop through five instar stages. After hatching, larvae seek and enter the roots of a pea plant. Larvae will enter and consume the contents of the nodules of the legume host plant. It is the nodules that are responsible for nitrogen-fixation which affect yield plus the plant’s ability to input nitrogen into the soil. Consumption of or damage to the nodules (Figure 4) results in partial or complete inhibition of nitrogen fixation by the plant and results in poor plant growth and low seed yields.

**Figure 4**. Damaged pea nodules (Photo: L. Dosdall).

Pea leaf weevil

Models runs predicting spring adult activity, oviposition and larval development for this pest are completed as of Week 9 (June 21, 2020). Use the following information to aid in-field scouting for larvae.

Adults will feed upon the leaf margins and growing points of legume seedlings (alfalfa, clover, dry beans, faba beans, peas) and produce a characteristic, scalloped (notched) edge. Females lay 1000 to 1500 eggs in the soil either near or on developing pea or faba bean plants from May to June.

Larvae develop under the soil and are “C” shaped and milky-white with a dark-brown head capsule ranging in length from 3.5-5.5 mm (Figure 2). Larvae develop through five instar stages. After hatching, larvae seek and enter the roots of a pea plant. Larvae will enter and consume the contents of the nodules of the legume host plant. It is the nodules that are responsible for nitrogen-fixation which affect yield plus the plant’s ability to input nitrogen into the soil. Consumption of or damage to the nodules (Figure 3) results in partial or complete inhibition of nitrogen fixation by the plant and results in poor plant growth and low seed yields.

**Figure 2**. Larva of pea leaf weevil in soil (Photo: L. Dosdall).

**Figure 3**. Damaged pea nodules (Photo: L. Dosdall).

Biological and monitoring information related to pea leaf weevil in field crops is posted by the province of Alberta and in the PPMN monitoring protocol.

Also refer to the pea leaf weevil page within the “Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide” – both English-enhanced or French-enhanced versions are available.