Notes on the laboratory rearing and biology of the wheat bulb fly, Leptohylemyia coarctata (Fall.)

The laboratory rearing of all stages in the life-history of the Wheat Bulb Fly, Leptohylemyia coarctata, (Fall.), is described. The object of this work was to provide suitable material, in particular eggs and larvae, for insecticide experiments. Details of a container suitable for ovipositing adults are given. Several diets for the adults were compared and it was found that the greatest number of eggs was produced when the flies were fed on beef blood and a mixture of sweetened condensed milk and honey. Females were found to lay up to 244 eggs each; egg-laying commences 9–15 days after emergence and continues almost as long as the females live, but reaches a peak 3–5 weeks after emergence. Some females survived from late June until early November. In a small laboratory population, the average number of eggs laid by each female was 29·9 and mean length of life was 26·3 days for males and 41·6 days for females.The eggs have a long obligatory diapause period. They have no effective water-proofing mechanism, but can recover from considerable temporary desiccation. A method of storage during diapause is described. The eggs normally hatch in late January or early February, but hatching can be delayed until much later in the year by storage below 0°C.The effects of temperature on larval and pupal development are described. Larvae will grow at 20°C., but pupating larvae or young pupae are rendered sterile unless kept at temperatures of 15°C. or below. It is shown how a combination of delayed hatching and rapid larval and pupal development can produce fertile flies at unusual times of the year in the laboratory. It is suggested that this may make it possible to produce young larvae in the autumn for insecticide experiments.In conclusion, some parasites and predators encountered in the field and the laboratory are mentioned.