As of May 31, 2020, model output indicates that hatch is well underway and both first and second instar larvae may be occurring in alfalfa fields across southern Manitoba and Saskatchewan (Table 1). The following graphs compare development for Winnipeg (Fig. 1) and Swift Current (Fig. 2). At Winnipeg (Fig. 1), AAW populations are predicted to be primarily in the second instar. Weevil populations near Swift Current (Fig. 2) are expected to consist mostly of first instar larvae. If present, the model predicts that populations in the southern Peace River region would primarily still be in the egg stage (Table 1).
Table 1. Predictive model output estimates for Hypera postica populations at selected sites across the Canadian prairie as of May 31, 2020.
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| Figure 1. Predicted alfalfa weevil (Hypera postica) phenology at Winnipeg MB. Values are based on model simulations (April 1-May 31, 2020). |
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| Figure 2. Predicted alfalfa weevil (Hypera postica) phenology at Swift Current SK. Values are based on model simulations (April 1-May 31, 2020). |
The map below (Fig. 3) indicates areas where populations should have second instar larvae (% of total population).
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| Figure 3. Predicted development of populations of alfalfa weevil (Hypera postica) across
the Canadian prairies as of May 31, 2020.
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Monitoring
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. 3, upper right).
