Can Insects Survive in a Greenhouse Over Winter

Winter is a rough time to be an insect. Insect metabolisms deal poorly with cold temperatures, slowing to a crawl as the temperature drops and eventually stopping outright.

A harsh winter can put a serious damper on insect numbers, which is often a good thing for farmers and gardeners who struggle with insect damage. Greenhouses, however, provide a protected environment that stays warm during the winter and can thus allow insects to thrive even in the dead of winter.

The two kinds of greenhouses in use, unheated and heated greenhouses, both provide excellent opportunities for insect survival over winter.

Unheated greenhouses and hoop houses heat up quickly in the spring and cool down slowly in the fall. They are effective at trapping heat from the sun and insulating the plants within from the harshest winter temperatures, despite not being actively heated.

Though unheated greenhouses do cool off in the winter and cooler temperatures will reduce insect activity, the protection provided by an unheated greenhouse can still allow insects to overwinter more successfully and emerge earlier in the spring.

Heated greenhouses are even better at keeping winter insect numbers high, even those of invasive insects from warmer regions. Tropical species of insects are very much unable to survive outdoors in temperate regions but can thrive in heated human structures over winter, wreaking havoc all winter and even dispersing back into the environment when warm temperatures return.

Heated greenhouses are excellent at providing a safe, warm home for insect populations and usually have a ready source of food, that being the plants that are being grown in the greenhouse. To make things worse, plant growth is much quicker in the warm environment of a heated greenhouse and thus there is more food for the insects to consume.

Insect infestations of greenhouse crops tend to be more severe than those outside. This is because insect populations can remain active in greenhouses far longer than they would be able to outdoors, allowing for more generations in a shorter period of time.

In addition, the confines of a greenhouse also tend to exclude the natural predators of insects, meaning that there are no checks on insect population. This increase in the number of insects can lead to serious damage to plants grown in greenhouses, both through the physical damage caused by herbivory and through the spread of plant diseases vectored by the insects.

Because it is so easy for pest populations to build exponentially in greenhouses it is vital for greenhouse owners to have a solid pest control plan. Insect exclusion is the best defense: preventing insects from entering the greenhouse in the first place can prevent insect damage.

This is why it is important that all entry points into the greenhouse be protected with mesh and all plants put in the greenhouse are inspected thoroughly to prevent them from smuggling insects pests inside. Because it is nearly impossible to notice all insect activity, monitoring for pests is the next most important step.

Plants should be regularly inspected for damage and traps should be placed to determine how high insect numbers are. If insect populations begin to increase, then chemical controls can be used.