Letter: No seasonal northward migration and mass influx of grasshoppers from Montana
By Letter to the Editor on August 6, 2021.
Dear editor, An article in the Lethbridge Herald on Aug. 3 said that grasshoppers “move north as the season progresses, meaning that the adults are here in time to lay eggs”, and describes “a lot of grasshoppers showing up in the fall” from Montana. It doesn’t work that way with grasshoppers, although some insects like the Painted Lady butterfly and Monarch are famously mobile on a northward seasonal path. A few grasshoppers going back and forth across the border often remain in the area, and are not the current crop species anyway. We can be sure that what we see developing in May and June will be what matures in July. Sometimes enough are swept up into wind that, like beetles and aphids, they can be seen on radar, as was the case on the southern Saskatchewan border in the first week of July. But an invasion is local and not related to the general problem in Alberta crops. Grasshoppers that hatch in Alberta grow up in the same general area, mate, and lay eggs. Montana grasshoppers rarely show up here, certainly not in an annual northward seasonal exodus, and if they do, they simply would add some. The grasshoppers present in Alberta this year hatched here, as did their parents, grandparents, great-grandparents, and so on. There were some unusual documented cases in the 1930s in which a species (lesser migratory grasshopper) that is not the main one now was increased in Saskatchewan and Alberta with migrants from the USA. It is not a significant factor for southern Alberta now. Since 1983, I have monitored multiple species at selected sites through the year, whenever I can make time for a field trip, observing eggs at the end of winter, then hatching in spring, to maturity (with wings) in summer. I’m sure others who worked with me (such as Craig Andrews, on the same studies 1983-2002,and many country field personnel) agree that our grasshoppers are almost entirely home-grown. We have monitored and identified tens of thousands, and produced tens of thousands of eggs from them to study annual changes, geographic differences, and new rational control methods. Since 2003, a fall survey is supervised by provincial entomologists (I supervised it 1983-2002), and what they and Alberta Fieldmen are counting are the ones that hatched and went through their five immature stages right in place. There may be a mixture along the border, or an occasional weather phenomenon aloft, but there is no seasonal northward migration and mass influx of grasshoppers from Montana. The current dominant species, the two-striped grasshopper, does not walk or fly more than a kilometer during a typical lifetime, up to a few under unusual conditions. If continued warming results in movements of significant numbers of grasshoppers over larger distances, it will be worth documenting with field observations, determination of annual and seasonal changes, and perhaps stable isotopes and DNA analysis. Dan Johnson Lethbridge 11-10
