Validation of degree day threshold for Delia platura first emergence in New York State

Seedcorn maggot (Delia platura) is a globally distributed agricultural pest that feeds on the germinating seeds of economically important crops, including corn and beans. The larvae cause underground damage, which can lead to stand loss. For decades, D. platura has been managed using insecticide-coated seeds, but following the ban on neonicotinoid-coated corn, soy, and wheat seeds in New York State, this practice will no longer be available. Degree day models have been used to predict the emergence of the overwintering generation of agricultural pests since the late 1900s. However, the terminology used in the literature to distinguish degree day thresholds for first emergence and peak emergence is unclear, and previous reports of a 360 degree day emergence threshold did not align with field observations. In 2023, we captured the first emergence at four sites, and in 2024, we monitored adult D. platura at 25 sites in New York State. We observed the first adult emergence between 52 and 197 accumulated degree days (98 ± 7 degree days, mean ± 1 SE) using a biofix of January 1st, confirming that in New York State, D. platura emergence is earlier than previously reported values. Additionally, we note adult activity during December 2023 and January 2024, suggesting that warming winters may impact our ability to predict pest emergence. We propose future models should incorporate both degree day information and other regionally specific factors known to impact pests, including farm management, soil conditions, and landscape composition, for more accurate predictions. • Delia platura is a widely distributed detritivore that damages the germinating seeds of crops, including corn and soy. • Following the ban on neonicotinoid-coated seeds in New York, predicting pest emergence will be informative for management. • Previous models report D. platura emergence at 360 degree days, but with no measures of variation. • Our data show the first emergence of D. platura in New York occurs between 52 and 197 degree days.