FIELD STUDIES ON THE INFLUENCE OF WEATHER ON EGG-LAYING BY THE CABBAGE ROOT FLY, ERIOISCHIA BRASSICAE BCHÉ. II

Observations on the intensity and duration of egg-laying by Erioischia brassicae Bché were continued in 1953 on the same site as in 1952. Eggs were first observed on 31 April and the spring peak period of egg-laying lasted from 3 to 30 May with a daily average of 40 eggs/plant. The mean total in spring 1953 was 1287 eggs/plant. Summer peaks occurred on 1–20 July (average 17 eggs/day/plant) and 5–11 August (average 21 eggs/day/plant).
In the field the threshold of reproduction was approximately 60° F. The rate of egg-laying was highest at 65–70° F. and it declined during prolonged periods of higher temperatures.
The annual cycle of generations, as shown by egg counts and confirmed by the examination of puparia, consisted of two generations and a partial third. The spring generation developed without a prolonged diapause, and there was complete emergence during the summer. The overwintering puparia came from the second and third generations of larvae.