As grasshoppers decimate fields throughout the province this year, the question of why echoes through the minds of many.
James Tansey, the provincial insect and vertebrate pest management specialist for the Ministry of Agriculture in Saskatchewan, explained that the grasshopper population each year is in direct relation to the weather conditions of the previous year.
“What we're seeing this year is a product of what we've seen in the weather this year, but more importantly, the weather we saw last year,” he stated. “We had significant grasshopper pressures in a number of parts of the province last year, primarily in the Southwest and South-Central regions. So, a lot of opportunities for boy-meets-girl, and they get a lot of eggs off into the ground.”
Grasshoppers thrive in dry, warm conditions, with a little bit of moisture and green plants to feed on.
When conditions remain dry throughout July and August, a significant amount of mating can occur, resulting in a lot of eggs being laid into the ground.
Tansey also noted that the late freeze last year allowed more grasshopper embryos to develop and survive over the winter.
“The warm temperatures allow those grasshopper embryos inside those eggs to speed along in their development,” he elaborated. “Much like you see with any embryo, they have to go through a developmental period, and it's all determined by temperature. If they get enough warmth during the course of the summer, especially late summer, then they can speed through their development and get to a point where they're really well along in their development and their success surviving the winter will be greater.”
In addition, the heat in early spring accelerated the development of grasshoppers within the province which resulted in an early hatch of the two striped grasshopper.
“Everything about them is determined by temperature,” Tansey explained. “So, their activity increases, their feeding increases, and their development is even faster.”
Typically, there are four predominant species of grasshopper within Saskatchewan. Those species are the Clearwing, Two-Striped, Packard’s, and a Species Concept (includes four species that are closely related).
“We're also seeing in northern regions a bit of an oddball with Bruner's grasshopper,” he noted. “This is occurring in northern and northeastern regions, and these are regions that are normally not terribly heavily influenced by grasshopper populations and they're starting to see some decent numbers of this species called Bruner grasshopper. So, in addition to our normal four, we've got this one present in northern regions as well.’
Looking forward, if dry, hot conditions persist, it is likely that many grasshopper eggs will be laid in the ground, meaning that continued grasshopper pressure is possible for next year. However, an early frost could impact how many develop.
“If we get an early frost the development of those embryos inside the eggs will be slowed, or it could stop entirely,” Tansey stated. “What they do is they go into a state called diapause, and it's a little bit like hibernation except that it's associated with Arrested Development. That embryonic development ceases when the temperature is too cold, and if it isn't far enough along, they won't survive the winter. So, if we do get an early, hard frost, that can have a negative impact on grasshopper populations for next year.”
Though not as influential as the weather, grasshopper populations can also be influenced by fungal pathogens, and a number of different predators such as the grasshopper mouse, Richardson's ground squirrels, and different species of bird.