Bionomics of the perilla leaf roller, Pyrausta phoenicealis HÜBNER

Abstract

The perilla leaf roller, Pyrausta phoenicealis HüBNER, is one of the injurious pests of perilla, Perilla ocymoides L. in Japan. The present paper deals with its developmental biology in relation to temperature and photoperiod and seasonal prevalence.
The larvae feeding on perilla leaves pass through four instars. The larval duration is about 2 weeks at 23°C. Threshold temperatures of development for the egg, larva and pupa were calculated as 10.9, 12.7 and 12.9°C, respectively, and effective thermal totals as 51, 156 and 89 day-degrees, respectively. Preovipositional period of the female moths is 3 days at 23°C. It is supposed, therefore, threshold temperatures and effective thermal totals for the successive developments during one generation are approximately 12°C and 328 day-degrees, respectively.
When they are reared from egg stage under short-day conditions, the larvae enter to diapause at the 4th stadium. The critical day-length for the induction of diapause is assumed as 13 to 14 hrs. The female moths survive for about 10 days and lay average 180 eggs at 23°C.
On the basis of these observations. it is suggested that the 4th instar larvae of the perilla leaf rollers hibernate in a state of diapause, and they have 3 or 4 generations a year in Taai region, central part of Japan.