Thursday, 8 June 2017

Weekly Update (Jun 8, 2017; Wk 06) - Alfalfa weevil

Alfalfa Weevil (Hypera postica) – Reminder - Biological information and photos of all life stages of this insect can reviewed on the Week 4 post.  The larval stage of this weevil feeds on alfalfa leaves in a manner that characterizes the pest as a “skeletonizer”.  

Degree-day maps of base 9°C are now being produced by Soroka, Olfert, and Giffen (2016) using the Harcourt/North Dakota models.  Models predicting the development of Alfalfa weevil across the prairies are updated weekly to help growers time their in-field scouting for second-instar larvae.  Compare the following predicted development stages and degree-day values from Soroka (2015) to the map below.

As of June 4, 2017, the recent warm weather has resulted in rapid development, indicating that 80% of the hatch is probably complete (less than 20% last week). Larval populations should be predominantly in the first and second instars (less than 10% are predicted to be third instars). 

Figure 1.  Heat units accumulated necessary for the development of Alfalfa weevil 
(Hypera posticaacross the Canadian prairies (April 1-June 4, 2017).

Remember - Use the photo below as a visual reference to identify alfalfa weevil larvae.  Note the white dorsal line, the tapered shape of the abdomen and the dark head capsule.

Alfalfa growers are encouraged to check the Alfalfa Weevil Fact Sheet prepared by Dr. Julie Soroka (AAFC-Saskatoon) and additional information can be accessed by reviewing the Alfalfa Weevil Page extracted from the "Field crop and forage pests and their natural enemies in western Canada - Identification and management field guide" (Philip et al. 2015).  That guide is available in both a free English-enhanced or French-enhanced version.