Ecological characteristics of the perilla rust mite, Shevtchenkella sp., that causes damage to Perilla frutescens (Lamiaceae) were studied under a range of temperatures. The mean generation times were 27.3, 15.4, 11.3, 8.8, and 7.8 days at 18, 21, 24, 27, and 30°C, respectively. The estimated lower thermal threshold was 12.8°C, and the thermal constant for egg-to-egg development was 133.5 degree-days. The intrinsic rate of natural increase (rm) was 0.1001, 0.1504, 0.2020, and 0.2146 at 21, 24, 27, and 30°C, respectively. The rm value was not calculated at 18°C as more than 70% of the mites failed to reach adulthood, and of those that did, only 2.6% laid eggs. Zero fecundity was estimated at 12.8°C based on regression analysis performed using the average number of eggs per female per day. Most females reared with a 13 h photoperiod at 21°Cin the laboratory were in diapause. The population of the perilla rust mite used in these tests in the laboratory was collected from Kochi Prefecture, Japan.
Fifty percent of the diapause females of the perilla rust mite collected from the field in Tokyo in 2015 were forecasted to appear in early October. The nymphs and adults were trapped outside two greenhouses on glass slides coated with high-vacuum silicone grease in Kochi Prefecture throughout the year, indicating that perilla rust mites disperse through air.
For the quantification of shiso rust mite (Shevtchenkella sp.) occurrence, which is difficult to be observed because of their tiny body size, a loop-mediated isothermal amplification (LAMP) assay was tested. Shiso rust mites on leaves were collected by rinses with ethanol. DNA was extracted from the washing solution and the LAMP assay was carried out using a specific primer set. This method enabled shiso rust mites detection from approximately 18% of the perilla mosaic diseased 116 strain. In addition, shiso rust mites in the air were collected using a wet trap. DNA was extracted from the trapping liquid and the LAMP reaction performed. The time during which turbidity increased was measured using a real-time turbidimeter, and it enabled to detect the peak of the occurrence of mites. Determination of the number of shiso rust mites scattered in the air revealed that they rapidly increase from July to September.