Friday, 19 June 2020

Predicted grasshopper development

Grasshopper Simulation Model Output – The grasshopper simulation model will be used to monitor grasshopper development across the prairies. Weekly temperature data collected across the prairies is incorporated into the simulation model which calculates estimates of grasshopper development stages based on biological parameters for Melanoplus sanguinipes (Migratory grasshopper). 

As of June 14, 2020, the simulation estimates that hatch varies between 14.5% at Grande Prairie and Lacombe to more than 85% at Winnipeg and Regina (Table 1; Fig. 1).  The prairie average, is 34% (20% last week) and well above the long term average of 10% (4.5% last week) for this point in the growing season (Fig. 1).  Across the prairies, populations are predicted to be 65, 18, 11 and 4% in egg, first, second, and third instars, respectively (Table 1).  

Table 1.  Predictive model output estimates for Melanoplus sanguinipes development (% of total population for each location) at selected sites across the Canadian prairie as of June 14, 2020.

Figure 1. Grasshopper hatch (%) based on model simulations using current environmental conditions (blue bars) compared to long-term normal (red bars) as of June 14, 2020.
*LTN = long term climate normals, used for comparison of current year development (OBS)

Grasshopper hatch is greatest in across the southern prairies; areas bound within the black line in the map below are those where 50% or more of eggs have hatched, according to the simulation model (Fig. 2).  
Figure 2. Predicted percent of grasshopper (Melanoplus sanguinipes) population at hatching stage across
the Canadian prairies (as of June 14, 2020). 

First instar grasshoppers are predicted to be present across the prairies, with first occurrence of hatchlings near Edmonton and southern Peace River region in the past week (Fig. 3).  Warmer conditions across southern regions of the prairies should result in appearance of third instar nymphs (Fig. 4).  

Figure 3. Predicted percent of grasshopper (Melanoplus sanguinipes) population at first instar stage across
the Canadian prairies (as of June 14, 2020). 

Figure 4. Predicted percent of grasshopper (Melanoplus sanguinipes) population at third instar stage across
the Canadian prairies (as of June 14, 2020). 

The two graphs compare development for Regina and Saskatoon.  The graphs illustrate that grasshopper populations near Saskatoon are predominantly in the first instar with relatively few grasshoppers in the second and third instars (Fig. 5).  Populations near Regina may be expected to have grasshoppers nymphs in first to fourth instar stages of development (Fig. 6).

Figure 5. Predicted grasshopper (Melanuplus sanguinipes) phenology at Saskatoon SK.
Values are based on model simulations (April 1-June 14, 2020).

Figure 6. Predicted grasshopper (Melanuplus sanguinipes) phenology at Regina SK.
Values are based on model simulations (April 1-June 14, 2020).

Biological and monitoring information related to grasshoppers in field crops is posted by Manitoba AgricultureSaskatchewan AgricultureAlberta Agriculture and Forestry, the BC Ministry of Agriculture and the Prairie Pest Monitoring Network.  Also refer to the grasshopper pages within the "Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and management field guide" (Philip et al. 2018) as an English-enhanced or French-enhanced version.