I achieved biofix today (May 9) in our orchard at the Meigs Farm near Lafayette. I have also talked to other growers who had also caught 3-5 moths or more in their pheromone traps. For me, I had caught one moth last week and caught three more over the weekend. This constitutes a sustained flight and thus we have biofix. The assumptions that go with biofix is that if we are catching male moths in the traps, female moths are also flying, are probably being mated, and are laying eggs. Because insects are cold-blooded, their development is primarily driven by heat. The warmer it is, the faster they develop. All insects have a developmental threshold, a temperature below which no development takes place. For codling moth, that temperature is 50o F. So if the temperature is less than 50o, no development takes place. Because growth of insects is temperature dependent, we measure their development in degree days rather than in days. A degree day is when the average temperature for the day is 1 degree above the threshold, so for codling moth, an average temperature of 51o means that that 1 degree day has been accumulated. When approximately 250 degree days have been accumulated after the egg was laid, it can be expected to hatch. Knowing the number of degree days helps to time your insecticide applications better. Please note the chart on page 29 of the Midwest Fruit Pest Management Guide (ID465). Insect growth regulators like Dimilin and Rimon should be applied at 50-75 degree days. Others, like Confirm and Intrepid should be put on at 100-200 degree days. A number of products should be applied at 150-250 degree days and the remainder should be applied at 250 degree days.
You can calculate degree days by taking the average of the high and low temperature for the day, dividing by 2, and subtracting 50. If the low is below 50 and the high is above 50, adjust the low to 50 and then divide by 2. If you are unsure about how to calculate degree days, follow me on Twitter at Rick Foster@PurdueFVInsect where I can be doing my calculation daily. Also, feel free to call or email if you have specific questions.