Issue 3, May 9, 2011

Weather Effects on Insect Pests

The cool weather that we have had over the past week have kept insects somewhat at a standstill. Most insects do not develop at temperatures below 50 degrees F. They just sit as in suspended animation, not feeding or growing. Although they do feed and develop at temperatures in the 50's, they do so much slower than when temperatures are in the 70's and 80's. Meanwhile, plants tend to grow at temperatures above 39 degrees F or so, allowing them to get ahead of their insect pests when temperatures tend to hang in the 40's and low 50's. Two or three weeks of this type of weather, commonly called a blackberry winter, can greatly reduce the impact of serious spring pests. Not only do the plants develop past the growth stage when insects cause serious effects, but insects are vulnerable to fungal disease and predation longer, resulting in fewer insects surviving.

Although freezing temperatures can have serious effects on many plants, they have little effect on spring-occurring insects. Plants and insects are damaged by freezing temperatures when ice crystals form within cells, puncturing cell walls. Insects respond to cool temperatures by reducing the amount of water in their cells, resulting in increases in the relative percentage of sugars and other materials, reducing the freezing point of the mixture. This is why ice cream is soft enough to dip when ice cubes taken out of the same freezer are very hard. The ice cream has a higher concentration of solutes which reduces the freezing point. In addition, insects produce long chain alcohols under cooling conditions including glycerol and ethylene glycol. Ethylene glycol is used as anti-freeze in car radiators. These alcohols also lower the freezing point of cell contents. Freezing temperatures during the summer will kill insects because they have not modified their physiologies.

In summary, the insect recommendations listed in last week's issue of this newsletter are appropriate for the coming week due to the lack of insect development. (Phil Nixon)

Phil Nixon

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