Will Our Warm Winter Weather Increase Insect Problems Next Spring?
Will our warm winter weather increase insect problems next spring? This is a common question many have asked because of the mild winter. I’ve also been asked the question in other years when we have had extreme cold winters, how will it affect insects the following spring and summer?
The answer to both of these questions is the same. Winter weather has very little influence on insect population the following spring.
The reason winter weather has little influence over subsequent insect populations is that insects have developed excellent strategies to survive. These strategies are grouped into two categories – freeze tolerant and freeze avoiding.
Freeze avoiding insects just don’t hang around or expose themselves to cold conditions. The classic example is the monarch butterfly. Monarchs migrate to Mexico in the fall. They avoid the cold weather and take advantage of the cheap pina coladas. While in Mexico, they reproduce, and that new generation migrates back north. Many of our significant insect pests such as armyworms, earworms, potato leafhoppers, and some aphids do not survive over the winter. These insects continuously reproduce in tropical and subtropical places and return with warmer weather.
Freeze tolerant insects are able to withstand freezing conditions. These insects accumulate biological antifreeze in their cells prior to winter. Insects use specialized carbohydrates as biological antifreeze. These compounds lower the freezing point of their body fluids. This prevents ice crystals from forming inside the insects’ cells. If ice crystals form, they will poke thousands of tiny holes in insects’ cell membranes. These tiny holes allow the highly organized cellular contents to get all mixed up and cause death. However, by lowering the freezing point of their cellular fluids, the insects can withstand freezing conditions down to -4 Fahrenheit without ice crystals forming.
We are familiar with many of these biological antifreezes, or sometimes called cryoprotectants. The two most common compounds are mannitol and glycerol. Mannitol is in many brands of chewing gum and is also used as a coating on the outside of hard candies. Glycerol is also common in our lives. It is in many soaps and lotions.
Some insects leave to avoid freezing conditions, and some adapt to the freezing conditions. And some insects tap into the geothermal heat to keep from freezing. Insects such as japanese beetles, june bugs, and dung beetles don’t leave, but they avoid freezing temperatures by burrowing into the ground.
Tunneling dung beetles like Onthophagus taurus burrow below the frost line in the soil and are thus not exposed to freezing conditions. The beetles emerge the following May when the threat of freezing temperatures are gone.
The best predictor of insect survival is the conditions during insect emergence. Insects are like us. They need food to survive. When they emerge from the winter, they need energy, they need food. For example, sometimes weather delays corn planting. This delay is detrimental to emerging corn rootworm larvae. They do not have a food source. This causes the first generation of the season to be greatly reduced. However, reductions of pest populations also limit the food supply for beneficial insects which feed on pest insects.
Really, insects are part of an interconnected web we call the ecosystem. We cannot look at just one parameter to predict how this interconnected system will respond to changes. However, our current conditions have very little influence on the upcoming spring and summer insect populations.