FACTORS AFFECTING THE BEHAVIOUR AND ACTIVITY OF THE CABBAGE ROOT FLY (ERIOISCHIA BRASSICAE BCHÉ)

The behaviour of cabbage root flies is governed by their need for food and shelter. Captive flies fed on sugar solution lived for periods up to 62 days, and a bred female laid 122 eggs.
Weather conditions determine the activity and the length of life of the flies. Feeding and egg-laying occur in warm sunny weather, and long periods of sunshine with temperatures of at least 60° F. in the latter half of April are associated with the onset of attack on the host plants. In cold or wet weather the flies shelter in soil or in thick herbage, and if they are immobilized for some time they die of starvation. In this way, the onset of cold weather checks the development of cabbage root fly attack. Details are given to show how the weather affected the activity of the flies in the springs of 1948–50 inclusive.
Eggs are laid in batches of varying size at irregular intervals during approximately 4 weeks. The position of the eggs about the host plants is affected by weather conditions. They are usually laid in the soil, but when the pressure of sunshine and drought is removed they are laid freely on aerial parts of the plants.
Knowledge of the influence of the weather on the activity of the flies enables attack to be anticipated with some degree of accuracy and control measures to be carefully timed.