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

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.

Keywords: Allium pests; forecasting model; hot temperature; phenology; summer diapause.

Figure 1

Hypothesized seasonal abundance patterns of D. antiqua by hot summer effect linked to the summer diapause behavior (i.e., aestivation). We hypothesized that the larger the hot summer effect, the more delayed the third generation.

Figure 2

Schematic diagram for the simulation process of the summer diapause termination and the emergence of pupae to adults in D. antiqua population. $r_s\left(T_{3di}\right)$ = completion rate model of summer-diapause termination, $r_p\left(T_i\right)$ = development rate model (1/days) of non-diapausing pupae, $f_P\left({px}_i\right)$= distribution model of pupal development time, ${px}_i$ = physiological age of pupae at i-th day, $f_s\left(x_i\right)$ = distribution model for the completion time of summer-diapause termination, $x_i$ = physiological age of pupae in summer-diapause at i-th day, and $T_{3di}$ = three-day moving average temperature.

Figure 3

Models describing the summer-diapause termination (SDT) in D. antiqua. The relationship between SDT development rate and temperature (A), distribution model of summer-diapause completion time by normalized time (B), and SDT density curves in relation to the days and temperature (C). The observed data sets were obtained from the published data of Ishikawa et al. [26].

Figure 4

Component models for the stage transition of non-diapausing pupae in D. antiqua. Development rate (1/mean development time in days) as a function of temperature (A), distribution model of development time (B), and predicted density curves of pupal stage transition in relation to age (day) and temperature (C) [7,25,26].

Figure 5

The predicted adults emergence of D. antiqua from summer diapausing cohorts (n = 1000) by the simulation model, comparing with the seasonal abundances. (A–C) in Jinju [51], (D) [50] in Naju and (E,F) in Jeju, Korea. The stage development is noted by the ✖ symbol: the first, second and third ✖ indicate the starting date of degree-day calculation at 10% adult emergence, the development until pupae (433.9 DD), and the completion of the egg–egg period (650.9 DD), respectively. The bent arrow on Figure (F) means backward tracking to the adult emergence from the late larval stage. The horizontal dotted lines indicate the critical temperature of 22.1 °C for SDT development.

Figure 6

Comparison of model outputs with actual observed data for predicting adult D. antiqua emergence. (A,B) are accumulated adult emergence curves from pupal cohorts in summer diapause in 1986 (n = 154) and 1987 (n = 155), respectively.