Tuesday, 12 June 2018

Pea leaf weevil (Jun 14, 2018; Wk 06)

Pea Leaf Weevil (Sitona lineatus– The PLW model predicts that oviposition is nearly complete and PLW are primarily in the adult and egg stages (Fig. 1). Larvae should begin to appear later this week. 
Figure 1.  Predicted pea leaf weevil phenology at Red Deer AB.
Values are based on model simulations, for April 1-May 28, 2018 (projected to July 15, 2018).

Pea leaf weevils emerge in the spring primarily by flying (at temperatures above 17ºC) or they may walk short distances. Pea leaf weevil movement into peas and faba beans is achieved primarily through flight.  Adults are slender, greyish-brown measuring approximately 5 mm in length (view weevil adult photos here).

Adults 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. 4).  Females lay 1000 to 1500 eggs in the soil either near or on developing pea or faba bean plants from May to June.

Figure 4.  Scalloped notching along leaf margins of pea plant (Photo: L. Dosdall).

Larvae develop under the soil over a period of 30 to 60 days. They are “C” shaped with a dark brown head capsule. The rest of the body is a milky-white color (Fig. 5 A). Larvae develop through five instar stages. In the 5th instar, larvae range in length from 3.5 - 5.5 mm. First instar larvae bury into the soil after hatching, and search out root nodules on field pea and faba bean plants. Larvae enter and consume the microbial contents of the root nodules (Fig. 5 B). These root nodules are responsible for nitrogen-fixation, thus pea leaf weevil larval feeding can affect plant yield and the plant’s ability to input nitrogen into the soil. 

Figure 5.  Pea leaf weevil larva in soil (A) and field pea root nodules damaged by larval feeding (B).  Photos: 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.  A review of this insect was published in 2011 in Prairie Soils and Crops by Carcamo and Vankosky.