Tuesday, October 28, 2008

Greenhouse - Temperatures and Insects

Growing cooler in the greenhouse can limit the development of some insect pests. However, the effects vary with insect type. The following are some common grenhouse insect pests and the effects of temperature.

Western flower thrips develop at temperatures above 50°F. At a temperature of 78°F to 82°F, the completed life-cycle from egg to adult is 12 to 14 days. As temperature decreases, time from egg to adult increases.

Green peach aphids can multiply in lower temperatures. A model has been designed for the development of green peach aphid, and we know that their development occurs when temperature is above 39°F and the rate of development increases until 89°F.

Twospotted spider mite development begins above 50°F. The optimum development temperature is between 85°F and 95°F, which explains why this pest is particularly a problem during warm weather and in hot greenhouses.

Greenhouse and silverleaf whitefly- - A model has been developed for the greenhouse whitefly, which states that development begins at a temperature above 47°F. Although the greenhouse whitefly and the silver leaf whitefly are different species, I believe the development temperatures are fairly close. There is a seven-day difference in time to development from egg to adult at 70°F in these two species.

The differences in the base temperature of each insect (the temperature at which development begins) enables us to determine the impact of lowering greenhouse temperature on insect populations. With a lower greenhouse temperature, insects with a lower base temperature would be impacted relatively less than insects with a higher base temperature. Therefore, populations of Western flower thrips and twospotted spider mites would increase at a slower pace at a lower greenhouse temperature compared to populations of green peach aphids. So, if you’re tempted to lower your greenhouse temperature, keep your eye out for aphids, as they will continue to develop relatively quickly compared to the other three insect pests.

Adapted from "How changing temperature influences greenhouse insect populations" by Jeanne Himmelein in the October, 2005 edition of the Greenhouse Alert Newsletter from Michigan State University.

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