Synthetic biology for genetic control of agricultural pest insects

The diamondback moth, Plutella xylostella, is the world’s major pest of brassica crops (e.g. cabbage, broccoli, cauliflower, pak choi, oilseed), with annual control costs and losses amounting to US$4-5 billion [1]. The damage is caused by larvae feeding on crop foliage, leading to yield losses or unmarketable produce. Present in all regions where brassica crops are grown, diamondback moth is difficult to control, largely due to its ability to rapidly develop resistance to insecticides. Implementing effective resistance management strategies can be difficult with a limited range of modes-of-action available, so new control tools are required.
Genetic technology has enabled the development of a method called RIDL (Release of Insects Carrying a Dominant Lethal) [4] as an alternative control method for pest insects. RIDL insects live as normal with a dietary antidote, but die as larvae without it. This allows for mass-production and mass-release of RIDL adult insects. After mating with wild counterparts in the field their progeny die, leading to population size reduction. A variant of RIDL, called fsRIDL, confers female-specific lethality so that large numbers of single-sex (male) moths can be efficiently produced; a process called ‘sexing’ [5]. Male-only releases improve per-male efficiency by focusing their mating efforts on wild females.
RIDL/fsRIDL is species-specific; offers effectiveness against difficult-to-reach and low-density target pests; and is also self-limiting in the wild. Survival of the male line also results in introgression of background genetics of the fsRIDL strain into the wild population. This has the potential to provide a powerful resistance management effect if the fsRIDL strain carries largely insecticide-susceptible alleles, essentially by diluting resistance genes in the wild population [6].
In current fsRIDL strains of diamondback moth, female-specific lethality is regulated by sex-alternate splicing sequences from the sex determination gene, doublesex [5]. Although mortality is highly specific to females and well-repressed by the chemical antidote in larval feed, females die as larvae, incurring costs through diet consumption.
This project will investigate alternative methods of engineering genetic sterility and female-specific lethality using custom-engineered restriction enzymes, going well beyond the present state of the art for insect synthetic biology. The project will build on the findings of a funded collaborative project between the University of Liverpool and Oxitec, which is working to identify sequences in the diamondback moth genome that might act as genome-editing targets for improved RIDL/fsRIDL. The student will continue analysis of the diamondback moth genome, and will develop constructs, develop transgenic strains of the moth and test for engineered phenotypes with potential value for genetic control. This is a project at the forefront of insect synthetic biology, and will expose the student to insect genomics, biotechnology, genetics, and population modelling approaches. Developing a new control tool in this major pest will provide proof-of-principle for new technologies for genetic control in Lepidoptera, with potential applicability to other important pest species, and significant potential value to sustainable agriculture.

Training:
The successful applicant will be based at the University of Liverpool and Oxitec, which is located in Milton Park, Oxfordshire. The student will gain expertise in synthetic biology, molecular biology, high-throughput sequencing and genomic analysis at the University of Liverpool, while will also benefit from the unique expertise of Oxitec in developing RIDL strains – Synthetic biology, microinjections, insect rearing and genetic manipulation.
Please direct informal enquires to Dr Alistair Darby ([Email Address Removed]) or Dr Ilik Saccheri ([Email Address Removed])