Friday, 2 June 2017

Weekly Update (Jun 1, 2017; Wk 05) - Pea leaf weevil

Pea Leaf Weevil (Sitona lineatus– This week is our PLW Blitz featuring this pest with:
  -The Insect of the Week
  -Updated model outputs and phenological predictions for 2017 (as of May 29, 2017), and 
  - A NEWLY UPDATED Monitoring Protocol (Vankosky et al. 2017)!

The PLW model was run for Lethbridge AB and Saskatoon SK. Current weather data was used then extended by Long Term Normal climate data (May 30-Jun 30) in order to predict pea leaf weevil phenology.  Compared to last week, model output indicated that oviposition has been delayed by ~5-7 days.  As of May 29th, phenologies for eggs and larvae were predicted to be similar for both locations (Fig. 1-2)

Figure 1. Pea leaf weevil model predicting phenology for 2017 near Saskatoon SK.

Figure 2. Pea leaf weevil model predicting phenology for 2017 near Lethbridge AB.

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 (Fig. 3, Left).  

The 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.  

Figure 3.  Comparison images and descriptions of four Sitona species adults including pea leaf weevil (Left).

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.

Biological and monitoring information related to pea leaf weevil in field crops is posted by the province of Alberta and a NEWLY UPDATED PPMN monitoring protocol is available!

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.