Biology and integrated management of bean seed fly

Bean seed fly (Delia platura) is a common pest of a range of crops grown in the UK and more widely including peas, beans, onions and courgettes. Its effects can be devastating. Bean seed fly has been highlighted by UK growers as a major problem on several crops, with peas and beans being the highest priority because of a lack of effective pesticidal control measures. A recent meeting of growers, agronomists, seed treatment specialists, researchers and members of the Agriculture and Horticulture Development Board (AHDB) team led to the conclusion that there was a need to explore a range of approaches to management and control of bean seed fly, since insecticidal options are becoming very limited and effective ‘silver bullet’ replacements may not be found. The project will be funded by the University of Warwick, PGRO http://www.pgro.org/ and AHDB https://horticulture.ahdb.org.uk/ and will provide opportunities for working with members of all three organisations and with growers, on an economically important issue.
Background
In the UK, bean seed flies overwinter as pupae in the soil. In early spring (March-April), flies start to emerge and after feeding and mating, the female lays her eggs just below the soil surface, generally singly. Females may lay as many as 40 eggs in a day. There is generally a period of several days before a further batch of eggs is laid. In the absence of a suitable host plant, the larva is able to complete development by feeding on decomposing organic matter. The larvae pupate in the soil at varying depths. The rate of development, and therefore the number of generations, depends on the ambient temperature. Bean seed flies can complete between 3 and 6 generations during the year according to the climate. Females prefer to lay eggs in freshly disturbed soil, especially where there are residues of vegetable matter or where large amounts of farmyard manure have been applied. The presence of plants is not required for bean seed flies to lay eggs.
Description of PhD
The aim of this PhD is to increase knowledge about, and understanding of, bean seed fly biology to underpin the development of an integrated strategy for bean seed fly control so that in the absence of pesticidal treatments this very damaging pest can still be managed effectively.
The PhD will address the following approaches/questions:
Improved understanding of the bean seed fly life-cycle and the influence of temperature/weather conditions. This is particularly related to the overwintering stage (what induces it and what ends it) and is to improve our ability to forecast the periods when bean seed flies are laying many eggs. It requires establishment of a culture of bean seed fly and experimental work in the lab to determine the relationship between fly development and temperature. The student will also monitor bean seed flies and record temperature data in the field to develop and ‘test’ weather-based forecasts. Here the aim is to determine, using simple modelling approaches, whether, for example, soil temperatures provide a better forecast than air temperatures.
Improved understanding of the behaviour and spatial distribution of bean seed fly. This will involve monitoring flies and sampling for the eggs/larvae at experimental sites and in commercial crops, as well as liaising with growers who are reporting damage to crops.
Approaches to reducing the size of bean seed fly infestations in susceptible crops. This is likely to be through cultural control methods including the timing of cultivations. Equally important is to understand what increases bean seed fly infestations. This will be through field work – either in small plot trials or in collaboration with growers.