Abstract
Plum pox virus (PPV), the pathogen of ringspot disease of the Japanese apricot, is transmitted by aphids. To identify the best periods for aphid control, we investigated the population dynamics of winged aphids in Inuyama City, Aichi Prefecture, where the ringspot disease of the Japanese apricot is common, and emergency control measures are in place between March 2015 and March 2018. The number of winged aphids in each field varied with the time of the year, increasing temporarily during the low-temperature period (January to March), and decreasing thereafter. In each field, the number of winged aphids tended to increase from May to June and from September to November, and decrease from July to August. The peak season occurred 3–5 times in 2015, 5 times in 2016, and 4–5 times in 2017. Furthermore, the estimated field values were determined using the state-space model for occurrence and development in each field was based on the number of winged aphids over the past three years. In the observed values, the peak of occurrence detected 2–5 times a year was smoothed to 2-4 times a year, and the emergence periods, which differed from field to field, nearly coincided. We also investigated the detection of PPV viruliferous winged aphids, using nested-RT-PCR, from March 2016 to October 2017. In a study involving a total of 1,002 individuals in each field, no positive specimens were confirmed. This suggests that the density of positive specimens at this survey site may have decreased due to the removal of infected plants for emergency control.
