Effect of chilling on the spring emergence of overwintering Eurytoma maslovskii (Eurytomidae: Hymenoptera)

This study investigated the effect of chilling temperature and duration on diapause termination in Eurytoma maslovskii, a major apricot pest in Korea and China. The experimental insects were sampled in mid-autumn. Overwintering larvae were subjected to a temperature range at -16, -4, 2, 9, 13 °C for 12 wk (a temperature of 19 °C was used for nonchilled control), and then exposed to cold temperature (2 °C) for different durations (from 1 to 16, 19, and 22 wk) at different times (20 September and 30 November) to determine adult emergence, prolonged larval diapause, and development rate postchilling. The results demonstrated a strong association between chilling temperature and duration with the emergence of E. maslovskii. It was observed that diapause may be terminated after at least 6 wk in the cold. However, the rate only reached a higher significance after 10 wk or longer duration of chilling. The optimal chilling temperature ranged from 2 to 9 °C. Late autumn chilling (mid-September) did not differ from winter chilling (late November). The postdiapause development rate of E. maslovskii was determined to be affected by the chilling duration and could be described by a 3-parameter probability density Weibull function. These results suggest that winter conditions play a crucial role in the phenology of E. maslovskii in spring.