The use of Sterile Insect Technique to increase the success of IPM in horticultural crops (HDC Studentship)

The tomato leafminer Liriomyza bryoniae (Kaltenbach) (Diptera: Agromyzidae) is an economically important pest of greenhouse tomato crops in the UK, which at high infestations can reduce the value of the crop by up to 20%. Sterile insect technique, SIT, is the release of sterile insects to overflood and mate with the pest population. Wild females that mate with sterile males lay eggs that contain dominant lethal mutations and are unable to develop into larvae. SIT has been proposed as a novel, alternative method of L.bryoniae pest suppression that could be used in conjunction with the current biological controls, such as Diglyphus isaea (Walker) (Hymenoptera: Eulophidae). This thesis presents information on the development of SIT against L.bryoniae and examines the feasibility and compatibility with existing pest management methods. Work was carried out that determined high quality, sterile adult L.bryoniae were produced when late stage pupae were irradiated with a dose of 160 Gy gamma radiation. Both male and female L.bryoniae were sterile after irradiation with 160 Gy, which is important given the current inability to separate pupae by sex. A multi-treatment cage experiment was used to compare bi-sex and male-only releases and showed that the release of sterile females did not have a detrimental effect and did not add to the pest problem. The multi-treatment cage experiment also compared the use of D.isaea with sterile male releases both separately and concurrently. Whilst the study conditions favoured the optimal environment for D.isaea oviposition and development, the concurrent release of sterile male L.bryoniae and D.isaea were compatible. SIT is a suitable method for L.bryoniae suppression; but further work to develop a more time and cost-efficient mass-rearing technique and greater knowledge of the market are required in order for it to become a financially viable pest management option. Overall, the irradiation of L.bryoniae pupae with 160 Gy produced sterile adults that have comparable fitness to wild-type adults, do not produce viable offspring and have the potential to suppress a L.bryoniae infestation.

The project will develop methods of incorporating the Sterile Insect Technique (SIT) into IPM programmes for UK horticultural crops. It is hypothesised that the use of this technique will slow down the initial population growth of specific pests, thus allowing natural enemies and/or released biological control agents more time to become established before pests reach critical economic damage thresholds. The choice of tomato / herbs / leafminer / Diglyphus isaea as the experimental system will ensure that the initial proof of concept studies will also have immediate benefit to the British horticultural industry by addressing an important current problem for both organic and conventional growers.

Work will consist of; the development of protocols for the sterilisation of the males to ensure both full sterility and competitiveness with wild males; determination of release ratios to effect control in experimental protected environments and preliminary full scale trials in a commercial greenhouse. The studies will build on previous work at Imperial College and overseas, which have indicated that SIT will have a very good chance of success in British crops