Impacts of Climate Change on Current and Future Crop Pests in Ontario

Tracey Baute, Field Crop Entomologist, OMAFRA

Climate change will have a direct impact on insect pests. Since insects are cold blooded, they are directly influenced by temperature. Those that feed on plants also rely on the availability of their host crops to survive. Though we have an idea of some of the impacts climate change will have on our pest populations, there are many unknowns that will make pest predictions more difficult. Here are just some of the factors we need to consider going forward:

1) Milder Winters

On average, our winters are getting milder. Yes, we still will have major storms that result in lots of snow. Looking at the average trends of winters over the last decade, we have experienced shorter and milder winter conditions. There are few extended periods of frigid temperatures that are harmful to overwintering species.

Milder winters increase the overwintering success of pests and will likely result in an increase in early season pests. Especially if we plant the crops they rely on earlier too. Many species of beetles overwinter in woodlots, leaf litter and the top 2 cm of crop residue. This includes pest species like bean leaf beetle, cereal leaf beetle, cabbage seedpod weevil and flea beetles which are predicted to be more of an issue in the future due to increased overwintering success.

Milder winters will also increase the likelihood that more insects can overwinter here. Pests that normally migrate in from warmer US states are already starting to overwinter successfully farther north. We know this to be true for black cutworm and true armyworm which are overwintering closer to us in Ohio, New York or Pennsylvania but models predict that corn earworm will also be able to successfully overwinter in the Great Lakes region due to climate change (Diffenbaugh et al. 2008). Stalk borer is another pest that may be able to expand its range to Ontario (Taylor et al. 2018).

2) Early and Longer Growing Season

Producers know first hand that crops are going in earlier and that the growing season is getting longer. Some of this is due to improvements in crop genetics and newer seed treatments that protect the seed and seedling in less ideal conditions. But earlier, ideal planting conditions are also resulting in host crops being planted earlier. This allows the early season pests that are successfully overwintering to easily find their food source and thrive.

Longer growing seasons are expected as temperatures increase. This will also speed up insect development, shortening the time it takes for them to go through their life stages from egg or nymph to adult. As a result, we could see some pests squeaking in an extra generation per year. Potato leafhopper, for example, is predicted to go through an extra generation per season here, especially if it arrives two to three weeks earlier than normal (Taylor et al. 2018).

Unfortunately, some natural enemies are more sensitive to changes in their environment, especially specialists that rely on one pest for a host. Parasitoids that rely on a specific life stage of their host may become out of sync with it, decreasing their chance of survival to the next generation. Higher temperatures and drier conditions can also be more detrimental to natural enemies than the pests. We may experience an imbalance in pests to natural enemies (Jeffs and Lewis, 2013).

An increase in pest pressure or generations per season could result in an increase in the number of pesticide applications per season. Hotter daily temperatures could negatively impact the effectiveness of some pesticides. Both can lead to pesticide resistance. We are also already starting to see resistant pest populations expand their ranges from the southern US into Ontario. This will lead to a greater need for new pesticides from different chemical families to rotate with. Increased use of pesticides could also negatively impact natural enemies, depending on which chemical families are used.

3) New Crops or Changes in Which Crops We Grow

Which pests will thrive most in a changing climate depends directly on what happens to their host crops. The more exclusive the pest is to one or two crops, the more vulnerable they are to any changes that occur to the crop. Bean leaf beetle, for example, is predicted to do well in Ontario’s future projected climate, but soybeans may only be able to be grown in limited regions, which significantly decreases the success rate for bean leaf beetle (Berzitis et al. 2014).

Invasive species are also predicted to be more of an issue as our climate shifts to be more like their host countries. We have already experienced several invasive insect introductions over the last two decades. Their chance of success increases if we also introduce their host plants as new crop opportunities. Change in consumer trends will have an influence. For example, the increased acreage and current demand for hemp, cannabis, and hops may influence European corn borer populations as more of its many host crops become more prevalent in Ontario’s crop landscape.

4) The Unpredictable – Extreme Events

Where it gets more difficult to predict future pest trends is with the extreme events. Climate change is not just about “global warming”. It is about extreme weather events like significant spring storms that bring record rainfall. Stronger wind events that flatten standing crops. Extreme heat waves with no rain in July and August. Record warm days in January or February that can kick an insect out of dormancy to find no food to feed on. Predicting the influences these will have becomes very difficult once you factor in multiple events in the same growing season.

As we learn more about each specific pest and their needs and limits, predictions will become accurate. What is clear is that careers in ecology, agronomy, entomology, pathology, plant science and climatic modeling are likely to still be essential for agriculture in the future.


Berzitis, E., J. Minigan, R. Hallett, and J. Newman. 2014. Climate and host plant availability impact the future distribution of the bean leaf beetle (Cerotoma trifurcata). Global change biology. 20. doi: 10.1111/gcb.12557.

Diffenbaugh, N. S., C. H. Krupke, M. A. White, and C. E. Alexander. 2008: Global warming presents new challenges for maize pest management. Environ. Res. Lett., 3, 044007, doi:10.1088/1748-9326/3/4/044007.

Jeffs, C. and O. Lewis. 2013. Effects of climate warming on host–parasitoid interactions. Ecological Entomology, 38(3), 209–218.

Taylor, R.A.J., D. A. Herms, J. Cardina, R.H. Moore. 2018. Climate change and pest management: Unanticipated consequences of trophic dislocation. Agronomy, 8, 7, doi:10.3390/agronomy8010007.