Cold spells might be hard to appreciate, but they are likely to help limit some pest populations.

A large amount of insect mortality occurs in winter.

Insects perish because of cold temperatures and natural diseases that attack them while they are in the resting stage.

Cold winters are known to restrict populations of some pest species, including bean leaf beetle, cereal leaf beetle and slugs.

If recent cold conditions persist, populations of these pest species are likely to be lower than usual come spring, but there is no guarantee.

Survival of slugs, for instance, is also influenced by the amount of snow on the ground because higher amounts of snow insulate slugs against colder temperatures.

The ultimate outcome will be difficult to predict.

For most pest species, however, the influence of cold winter temperatures and lots of snow is likely to be minor.

Grubs, for example, overwinter as larvae and many are killed by a pathogen that infects their outer skin, which desiccates (dries out) the body.

Some insects, which normally overwinter in surface residue (leaves, weeds, etc.) or soil don’t locate themselves deep enough in the soil to survive winter and can be killed by cold temperatures.

This winter, which has been so severely cold, may cause a decrease in the number of insects that overwinter and may bring decreased insect pressure this growing season.

On the other hand, if we have a period of mild weather, this forces some insects to start growing and then if the weather turns sharply cold, many insects will perish.

A lot depends on the temperatures in February, the particular insect, and if snowfall occurs.

Snow insulates the soil and lessens the mortality of insects.

Many pest species are well-adapted to living in our climate, whereas others visit only for the growing season and do not get to experience our winter.

For instance, many insect pest species that can cause economic damage in Pennsylvania, for example, potato leafhopper, black cutworm and armyworms, are migratory and come to Pennsylvania from southern states where they spend the winter.

The region’s weather, therefore, will not influence their survival at all; it is their local overwintering conditions further south that matter.

For pest species that have been established in the region more recently, we have a relatively poor understanding of the influence of winter temperatures on their populations.

Cold temperatures can knock back some pest species, but the outcome can be hard to predict.

When spring arrives, gardeners will need to rely on regular bouts of scouting to understand area pest populations and determine which species, if any, threaten our gardens.

But in the meantime, bundle up against the cold and hope that the cold weather continues to at least lower insect populations in the coming year.

“Growing Green” is contributed by Diane Dorn, Lehigh County Extension Office Staff, and Master Gardeners. Information: Lehigh County Extension Office, 610-391-9840; Northampton County Extension Office, 610-813-6613