Evaluation of Degree-Day and Julian-Day Logistic Models in Predicting Cabbage Maggot (Diptera: Anthomyiidae) Emergence and Flight in Upstate New York

A 2 yr (1999–2000) study using water-pan traps in the field indicated four generations, including the spring generation, of cabbage maggot adults, Delia radicum (L.), in upstate New York. On average over the 2 yrs, an accumulation of 160.7 ± 8.1 degree-days and 120 ± 3 Julian-days was required for the first adult emergence of flies from overwintered puparia (spring generation). The emergence of 10% of the population required a mean accumulation of 176.6 ± 3.8 degree days and 122.0 + 1.0 Julian days, 25% emergence required 204.2 ± 2.3 degree days and 125.0 ± 1.0 Julian days, 50% emergence required 251.3 ± 3.5 degree-days and 129.3 ± 1.5 Julian days, 75% emergence required 297.6 ± 30.4 degree-days and 132.0 ± 0.0 Julian days, and 95% emergence required 390.9 ± 10.1 degree days and 141.0 ± 3.0 Julian days. From the emergence of the first adult flies, the population required a mean accumulation of 449.2 ± 1.4 degree days to complete the spring emergence. For complete emergence of flies, the F1 generation required a mean accumulation of 508.4 ± 32.9 degree days, the F2 generation required 465.3 ± 21.5 degree days and the F3 generation required 399.1 ± 3.1 degree days. With the help of a degree-days model, it is possible to predict fly emergence in the spring and succeeding generations. This model can help growers minimize insecticide use through better timing of treatments or adjustment of planting dates. In addition, this model will be useful in developing sampling plans and control strategies for immature stages of cabbage maggot.