Mass-rearing high-quality insects for field applications

This is an exciting time for applied insect genetics and the control of pest insects. For decades, various genetic control strategies have been proposed to control insect vectors of plant, livestock and human disease. However recent developments in recombinant DNA and transgenesis technologies have opened the door to practical interventions that would have been impossible only a few years ago, and the first of these are approaching field use. Each of these strategies involves the release of large numbers of engineered insects into the environment, to mate with wild insects. The outcome from there depends on the strategy. In Oxitec's 'RIDL' technology, all the progeny (or all the female progeny) die, leading to population suppression if sufficient engineered insects are released for a sufficient period of time [1,2]. Some other approaches aim to introgress genes into the wild population to make wild insects less competent as disease vectors [3]. A key gap in all these strategies is the ability to rear and release sufficient insects to have an impact on the target population. Although different strategies need different numbers of insects, insect populations tend to be numerically large, so most strategies require the release of millions of insects to have the desired effect in a reasonable time, some require far larger numbers. Large-scale rearing of pest insects has been developed primarily for the Sterile Insect Technique, with production levels >2 billion per week for the Mediterranean fruit fly, and ~200m/week for a few other species [4]. The biggest gap in this respect is for mosquitoes. Though traditional small-scale rearing is adequate for most laboratory purposes, it is relatively space- and labour-intensive and would be prohibitively expensive if attempted at a large scale. The student will attempt to remedy this by developing a scalable, modular rearing system, adaptable to many species, based on methods and principles from agricultural SIT programs, together with Oxitec's preliminary work in this area. As well as the obvious input questions, e.g. how to rear larvae and adults at high densities, how to optimise egg production from adults, the student will also look at output measures. In particular, we are concerned about quality of insects, not just quantity. Measurements of quality will also be developed, both cheap proxy measures such as pupal size and weight, and more sophisticated assays, such as mating competitiveness. These correspond to 'routine' and 'periodic' tests in modern SIT practice [5]. The student will also consider, mainly on a theoretical basis, strategies to assure strain stability in mass-rearing, starting with the 'filter rearing system' developed for translocation-based genetic sexing strains of Medfly [4]. Since mass-rearing produces intense selective pressures, this is an important area, and one where genetic theory and modelling can play a valuable role, with relevant data likely to be forthcoming within the timescale of the project. This project is timely as the first GM insect strains (Oxitec's RIDL strains) are nearing field use. The academic partner is working with Wolbachia-infected (non-GM) strains, which face similar issues of scale-up, stability etc. These two strategies will likely be first into the field, and so the first where the lack of rearing technology will be felt. Conversely, it is likely that the student will be able to take some of their work beyond the laboratory to pilot-scale mass production and actual field programs, at least on a pilot scale. 1 Alphey, L, et al. In Transgenesis and the management of vector-borne disease Aksoy, S, Landes Bioscience 2007 2 Thomas, D. et al. Science 2000, 287, 2474-6 3 Sinkins, S.; Gould, F. Nature Reviews Genetics 2006, 7, 427-35 4 Sterile Insect Technique Dyck, V. et al., Springer, 2005 5 FAO/IAEA/USDA Manual for product quality control and shipping procedures for sterile mass-reared tephritid fruit flies v5.0, 2003