Alfalfa weevil

Alfalfa Weevil (Hypera postica) – Degree-day maps of base 9 °C are produced to predict the development of Alfalfa weevil (AAW) across the prairies.  The model is updated weekly to help growers time their in-field scouting for second-instar larvae. 

Model output indicates that oviposition is well underway and initial hatch should occur over the next 7-10 days  (Fig. 1). Compared with long term normal weather data, egg development is 1 – 2 days later than average.  Based on the alfalfa weevil degree day model (Soroka et al. 2020), AAW development is most advanced across southern AB.

Figure 1. Predicted alfalfa weevil (Hypera postica) phenology at Saskatoon SK.
Values are based on model simulations (April 1-May 18, 2020).

Figure 2. Predicted development of populations of alfalfa weevil (Hypera postica) across

the Canadian prairies as of May 18, 2020. 

The larval stage of this weevil feeds on alfalfa leaves in a manner that characterizes the pest as a “skeletonizer” (Fig. 3, lower left).  The green larva featuring a dorsal, white line down the length of its body has a dark brown head capsule and will grow to 9 mm long (Fig. 33, upper right).  

Figure 3.  Developmental stages of the alfalfa weevil (Hypera postica); overwintered adult (upper row L-R), eggs, larvae, larva feeding or "skeletonizing" alfalfa leaf (lower row L-R), pupa within lacey cocoon, pupa, and newly emerged adult.

Alfalfa growers are encouraged to check the Alfalfa Weevil Fact Sheet prepared by Dr. Julie Soroka (AAFC-Saskatoon).  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. 2018). The guide is available as an English-enhanced or French-enhanced version.