Insects and other arthropods are cold-blooded (or more technically, poikilothermic), which means that they don’t generate their own body heat like we do, but must rely on the environment for their heat. Each insect has its own developmental threshold, a temperature below which no development takes place. For many insects, such as codling moth, that threshold is about 50o F. So, whenever temperatures below that temperature, codling moth is not active and no development is occurring. Other insects have their own developmental thresholds. In general, the warmer the temperature, as long as it is above the developmental threshold, the more rapidly insects develop. Most insects have an upper limit, above which developmental rate doesn’t increase or may even slow down.
This reliance upon temperature for development is why we make our recommendations for management actions, whether putting out pheromone traps or making applications, based on the crop stage rather than on calendar date. While the developmental rate of the crop doesn’t exactly parallel all the pest insects, it gives a pretty good approximation that we can use to determine when to act. Obviously, this year, insect development just like plant development is way behind where we were at this time last year, so we have to adjust the timing of our pest management activities appropriately.