XENIA — Warmer than average winters often bring predictions of higher than normal insect populations developing in the spring, and whether this is true or not, is a topic of much confusion among community members.
Though, for some insects, this prediction does fair true, for others, a complex of environmental factors dictate the population size and winter survival of insects.
Many insects over-winter as eggs, like the praying mantis (Mantis religiosa) and bagworms (Psychidae spp.), are generally on branches in highly exposed places and are sensitive to warmer temperatures causing pre-mature hatching and use of resources, in the case of the mantid. The bagworm, being more southern in origin hatches based on other environmental triggers making mild winter a suitable over-wintering environment.
The woolly bear caterpillar (Pyrrharctia Isabella) also temperature dependent indicating the warmer winter days could cause pre-mature activity forcing them to use stored fats they depend on to survive until spring. Without available food or stored fat, the woolly bear caterpillar would starve, potentially impacting the spring population negatively.
Insects that overwinter above the ground like the bean leaf beetle (Cerotoma trifurcate) do so in the adult stage and many are more likely to survive in the warmer temperatures. But if there is below freezing temperatures without snow cover, there could be less bean leaf beetles adults than during years with heavy snows to insulate them.
Japanese beetle grubs (Popillia japonica) overwinter below the ground where the soil temperature is more consistent. They may not be affected by the mild winter, although an argument can be made that the lack snow insulating them could lessen their chances of survival. But the temperatures may not have been cold enough, long enough to penetrate very deeply into the soil so the insulating snow would not be needed.
Remember all of the conditions discussed above also affect the population of beneficial insects, diseases and parasites. This in turn, will impact the pest population during the summer time.
When spring does arrive, the weather conditions then can have the greatest effect on the insect population. Insects need food to survive when they emerge and any delay of their food source will have more of an effect on the insect population than the weather conditions during the dormant winter months.
When everything is considered, winter temperatures are not the only factor influencing the insect population for the upcoming summer. It is more complicated and inter dependent on many factors. So in the end, we will have to wait and see!
For more information contact: Kim Hupman, Horticulture Program Assistant OSU Extension Greene County, 937-372-9971 ext. 128 or [email protected]