Features Insect Pests Top Crop Summit
Top Crop Summit speaker series: 2023 insect watch

Tyler Wist is a research scientist in field crop entomology with Agriculture and Agri-Food Canada in Saskatoon. Wist and his team develop integrated pest management tools and solutions to sustain the economic and environmental viability of farming systems in Western Canada.

The 2021 drought was hugely impactful on Prairie agriculture, and it had impacts on insect pests, as well. Some insects thrive in hot and dry conditions, while others suffer. In 2021, growing season temperatures were up to 3C higher than average, and precipitation was extremely low with some areas receiving four inches (100 mm) or less of rainfall. Many areas had a drought intensity of one in 25 or one in 50 years. 

Whether a pest insect thrives or dies depends on its lifecycle, its thermal tolerance and the response of its natural enemies to weather. 

Insects that don’t like drought include wheat midge, Swede midge, striped flea beetle, pea aphid, pollen beetle and cabbage seedpod weevil. Drought lovers include wheat stem sawfly, grasshoppers, crucifer flea beetle and lygus bugs.

During Top Crop Summit, Wist compared pea aphid populations in 2020 and 2021. In late-July 2020, almost 700 pea aphids per 10 sweeps were found in lentils at the Saskatoon Experimental Farm. In 2021, the number was one pea aphid per 10 sweeps on the same day one year apart.

Wheat midge development is tied to moisture, and the insect requires about one inch (25 mm) of rainfall in the spring for the cocoon to break dormancy and begin its development. As part of a research project in collaboration with SeCan, #midgebusters is trying to match the provincial forecast maps in Alberta and Saskatchewan to actual emergence and population counts on pheromone traps. Contact Wist if you would like to be part of the project in 2023.

Fall soil cores provide a forecast of predicted wheat midge infestations the following year. For 2021, predictions were for substantial wheat midge outbreaks across the Dark Brown and Black soil zones of Alberta and Saskatchewan. However, as it turned out in 2021, areas where wheat midge populations were high were those that received spring rainfall, such as Regina and southeast Saskatchewan, which had 2.5 inches of rain in May. Conversely, the Melfort area, where the forecast was for high populations, received little spring rain, and as a result, low midge numbers.

The wheat midge forecast for 2023 , along with other insect risk maps, can be found at the Prairie Pest Monitoring Network website, prairiepest.ca.

Wheat stem sawfly is a dry season pest. It has been around for 100 years as a pest in Western Canada. The economic threshold for growing solid-stemmed wheat varieties is if the previous year’s wheat crop had 10 to 15 per cent cutting at harvest.

Research by Weiss, Vankosky and Olfert (2022) looked at how climate change could impact wheat stem sawfly. Under the current climate, the southern Prairies, typically the Palliser Triangle, provides a very favourable climate. Using CSIRO Mark 3.0 modelling, by 2030, much of the Prairies would be very favourable, with northwest Alberta and the Peace River region being favourable to moderate. By 2070, even the Peace River region would provide a very favourable climate.

Alberta conducted a wheat stem sawfly survey in the fall from 1926 until the 1940s, and was resumed in 2003. The surveys can be found at the PPMN website. And, Sask Wheat is now funding a survey in Saskatchewan.

It won’t come as a surprise to many, but grasshoppers also like hot and dry conditions. Historically, grasshopper outbreaks have occurred during droughts because they develop faster and lay more eggs. Hot and dry conditions also negatively impact the fungal pathogen, Entomophaga grylli that helps control grasshoppers.

The migratory and two-striped grasshoppers were the two mains species of grasshopper pests last year. Many other species are not pests. The 2023 grasshopper forecast suggests pressure could be strong in the west central part of Saskatchewan.

Lygus bugs are another insect pest that likes dry and hot conditions. This complex of four species puncture plant tissue and suck plant juices, causing flower abortion and seed damage. They are pests of many different crops, including canola, alfalfa, hemp, sunflower, quinoa, faba bean and flax.

The oldest fourth and fifth instar and adult stages cause the most damage. Lygus needs about 110 growing degree days (GDD) to move from the first to fourth instar. By July 20, 2020, only 90 GDD had been reached in Saskatoon. In 2021, the drought and heat drove earlier populations of adult lygus bugs when GDDs had reached 157 by July 20.

The two main species of flea beetle that cause damage to canola crops are the striped and crucifer. Striped flea beetles prefer cooler and wetter conditions found more in the Black soil zones. Crucifer flea beetles prefer warmer and drier conditions. Research found that during the drier years of 2004 through 2010, crucifer flea beetles dominated the populations on the Prairies. Higher moisture conditions from 2011 to 2015 found a shift to a higher proportion of striped flea beetles. In 2021, at AAFC Saskatoon during the drought, striped flea beetle populations were negligible, while cruciferous populations spiked upwards to 1,200 beetles per two sweeps.

Wist encourages agronomists and farmers to sign up for the Prairie Pest Monitoring Network at prairiepest.ca to view forecast maps and pest status, and receive timely risk warnings.