A New Perspective to Understand the Late Season Abundance of Delia antiqua (Diptera: Anthomyiidae): A Modeling Approach for the Hot Summer Effect

SIMPLE SUMMARY: The onion maggot, Delia antiqua, is an important pest of crops belonging to the Allium genus worldwide. It is known that high temperature has a significant effect on the development of this pest, but how temperature conditions affect population abundances in the field environment has not been fully understood. Our model, which incorporated the hot summer effect into the model of summer diapause termination, showed that high temperatures in summer clearly delayed or suppressed the late season occurrence. This phenomenon was observed largely in the Jinju and Jeju regions of Korea, while it was not obvious in regions with cooler summers such as the United States, Canada, and Germany, where the occurrence peaks were overlapped or slightly separated between the generations before and after summer. Thus, our results provide a new perspective from which to understand the late season abundance of D. antiqua. ABSTRACT: The onion maggot, Delia antiqua (Meigen), is one of the most important insect pests to agricultural crops within Allium genus, such as onions and garlic, worldwide. This study was conducted to understand the seasonal abundance of this pest, with special reference to the hot summer effect (HSE), which was incorporated into the model of summer diapause termination (SDT). We assumed that hot summer temperatures arrested the development of pupae during summer diapause. The estimated SDT curve showed that it occurred below a high-temperature limit of 22.1 °C and peaked at 16 °C. Accordingly, HSE resulted in delaying the late season fly abundance after summer, namely impacting the third generation. In Jinju, South Korea, the activity of D. antiqua was observed to cease for more than two months in the hot summer and this pattern was well described by model outputs. In the warmer Jeju Island region, Korea, the late season emergence was predicted to be greatly delayed, and D. antiqua did not exhibit a specific peak in the late season in the field. The abundance patterns observed in Korea were very different from those in countries such as the United States, Canada, and Germany. These regions are located at a much higher latitude (42° N to 53° N) than Korea (33° N to 35° N), and their HSE was less intense, showing overlapped or slightly separated second and third generation peaks. Consequently, our modeling approach for the summer diapause termination effectively explained the abundance patterns of D. antiqua in the late season. Also, the model will be useful for determining spray timing for emerging adults in late summer as onion and garlic are sown in the autumn in Korea.