1975 Volume 19 Issue 3 Pages 144-148
Diapause in Oligonychus ununguis (JACOBI) at Hiratsuka, Kanagawa Prefecture, was broken by chilling the eggs at 10°C for 75-100 days, at 15°C for 100-120 days, at 4.5°C for about 120 days, or at 0°C for over 120 days. Winter eggs of this mite were collected from a chestnut orchard of the Fruit Tree Research Station at 15- or 30-day intervals from early November to mid-March and incubated at 25°C. It was found that most winter eggs failed to hatch before January, but their hatchability increased in the later season and reached the maximum between late February and early March. From these results, it was assumed that diapause in O. ununguis is terminated by early March. The relation between temperature and velocity of development of the eggs was linear between 15 and 27°C after the termination of diapause. Based on this relation, the threshold of development was estimated at 5.6°C and the total effective temperature for development from the termination of diapause to hatch was 270.3 degree-days. The hatching time of the winter eggs, predicted by the sum of effective temperature above 5.6°C from March 1 at Hiratsuka, coincided well with the observed dates of 50% egg hatch, April 27 in 1969 and May 2 in 1970.
