COLONISATION, DOMESTICATION AND POPULATION CONTROL IN PEST INSECTS

Safeguarding world food supplies is a grand challenge. It is therefore of great importance to develop safe, environmentally friendly and effective new techniques for tackling pests of agriculturally important crops. An existing method that has been very important is the sterile insect technique (SIT), in which insects are mass reared, sterilised by irradiation and released in large numbers. Sterile released males mate with wild females, and because these matings produce no offspring, the size of the pest population is reduced.

SIT has been applied with some great successes - but also notable failures. To circumvent known problems (for example, the loss in health that results from sterilizing males with irradiation) there is increasing interest in the application of Genetic Modification (GM) technologies. One of these is known as the Release of Insects with a Dominant Lethal (RIDL), invented by the Project Partner (Oxitec). In this, males can be released without sterilization, and the released individuals are easy to track in the field via fluorescent markers. RIDL works because the released males carry a transgene that causes daughters that inherit it to die during development, an effect that can persist for several generations. The lethality is focused on females because they spoil crops and fruits when laying eggs.

However, one potentially significant hurdle remains. To release large numbers, pest insects are domesticated and mass reared in laboratory facilities. This inevitably selects for individuals that are highly successful in the laboratory, rather than in the field (the released males must locate and mate with wild females for the technique to work). Unsurprisingly, there are several examples of poor field performance of SIT males and/or wild females preferring not to mate with them.

Despite widespread knowledge of these drawbacks, there has been no study of adaptation to laboratory conditions for pest insects used for SIT-based approaches in real time, in order to understand, and hence minimize, unwanted changes in key life history traits.

In addition, it is increasingly clear that a significant contribution to health comes from associations with gut bacteria. In insects, gut bacteria have widespread and surprising effects, e.g. they can alter host lifespan, mate choice, reproductive physiology, development and metabolism. Such effects also often depend upon diet, and the diversity of gut bacteria is diminished when insects are brought into the laboratory and eat less varied foods. However, there has also been no systematic study of changes in gut bacteria during domestication and hence the knock-on effects on hosts, e.g. on their ability to suppress pest population size. Changes to gut bacteria are therefore an important component of laboratory adaptation. They are of particular interest in the context of RIDL, in which the expression of female lethality is controlled by use of a dietary antibiotic. This will - as a side effect - also alter the effects and diversity of gut microbes.

We therefore need to understand how hosts and their gut bacteria adapt to laboratory mass rearing conditions. With this knowledge, undesirable effects of such adaptation can be slowed or reversed. The main objective is therefore to use the medfly (an agricultural pest of world-wide importance) to document changes in life history, gut bacteria, and their interaction, upon colonization to the laboratory and the ability to achieve population suppression.

The specific aims are:
1. Test the performance of wild individuals subject to 30 generations of colonization to the laboratory, under variable food regimes.
2. Test associated changes in the gut bacteria of the individuals under 1.
3. Test for differences in the effects of manipulating gut bacteria on individuals maintained under either stable or variable dietary regimes.
4. To assess the feasibility of probiotics to restore bacteria lost during colonization.

Insects destroy millions of tons of crops each year. At a time when safeguarding world food supplies is a grand challenge, this provides an urgent stimulus to develop new methods to tackle pests of agricultural importance.

There is increasing interest in Genetic Modification technologies such as the 'Release of Insects with a Dominant Lethal' (RIDL) invented by the Project Partner. RIDL offers potentially significant improvements over existing methods such as the sterile Insect technique (SIT) - e.g., removes the need for sterilization using damaging levels of irradiation. However, as with SIT, RIDL insects are generated from mass-reared, captive-bred individuals whose life history is very different from that of the wild population. Unsurprisingly here are numerous examples of poor field performance and/or mating discrimination against SIT males. A significant contribution to host fitness comes from from their associations with commensal gut bacteria. This is of particular interest for RIDL strains that utilize gene promoters controlled by dietary tetracycline. Such antibiotics will, as a side-effect, reduce gut bacteria - hence the maintenance of RIDL strains is necessarily associated with altered, potentially reduced, gut microbe diversity.

In order to investigate a fundamental component of successful population suppression using techniques such as SIT and next generation RIDL, it is therefore essential to understand how hosts and their gut microbiota (co-) adapt to mass rearing conditions in the laboratory. Armed with this knowledge, the undesirable effects of such adaptation can be slowed or reversed - producing flies for release that are more similar to their wild counterparts.

The main objective is to use the medfly (a global agricultural pest) to document effects on life history, and its interaction with gut bacteria, of colonization to the laboratory under different nutritional regimes, and ultimately the ability to achieve population suppression.

The School of Biological Sciences at UEA is committed to raising the economic and societal impact of its research. Co-I Hutchings was recently appointed Director of Enterprise for the School of Biological Sciences. Hence we are well placed to identify and maximise enterprise opportunities of this research.

1. WHO WILL BENEFIT FROM THIS RESEARCH

We anticipate 4 main areas for potential impact:
(i) Domestication: the evolutionary trajectory of changes that occur upon domestication is of broad interest across many different fields.
(ii) (Co-) adaptation of hosts and gut bacteria to novel regimes: We do not expect coevolution in the loose associations between between hosts with low food specialization and their commensal gut bacteria. Yet, a substantial body of research shows significant effects of gut bacteria on hosts even in such flexible associations - does this occur through previously ignored co-evolutionary mechanisms, or is it a side effect? In contrast to the well-known work on insects and their bacterial endosymbionts, the proposed work therefore offers a new opportunity for testing these highly important relationships between insects and microbiota. The work is therefore of considerable interest in evolution and microbial ecology.
(iii) Husbandry practices for insect control: There is a strong applied context in terms of increasing the reproductive performance of insect pests that are mass reared for control. This will therefore be of interest to workers in the pest industry.
(iv) Microbial ecology: there is much interest in describing new niches and bacterial communities and this work would contribute significantly to that.
(v) Probiotics: there is intense interest in the possibility of improving health by supplementing diets with beneficial bacteria. This work will provide data on whether this approach is useful for restoring bacteria lost during transitions to domestication. This is also a topic of significant public interest.

The main beneficiaries with whom we aim to maximise the impacts of the research above are:
1. Academia: we aim to maximise impact of the research described above through open access papers, reviews, commentaries, lab research web sites etc. For this project, we plan a research blog to which the research team and particularly the PDRA would contribute.
2. Private sector: we have already developed contacts in the private sector in a NERC-funded CASE studentship together with the Project Partner Oxford Insect Technologies (Oxitec). The contribution of the Project Partner to this project is invaluable in this respect. We plan to further increase impact by attending the next Fruit flies of Economic Importance conference in 2014 (in Bangkok, Thailand) and offer a talk (TC) and poster (PL).
3. General public, schools: We have recently devised new exhibition materials using pest insects for open days at UEA. We plan to develop these following further 'road testing', at the Royal Society exhibition in the summer of 2013, in order to develop teaching resources for use in the Teacher Scientist Network (TSN) scheme co-ordinated by colleagues at the John Innes Centre. Together with our Engagement Director, we are tailoring these resources to the National Science Curriculum.

2. HOW WILL THEY BENEFIT FROM THIS RESEARCH

The beneficiaries named above will benefit through:
(i) Increased economic competitiveness of UK plc through increased visibility of research outputs and increased engagement with applied research in the private sector.
(ii) The impacts are likely to be primarily of academic and public interest. Here the beneficiaries will gain through enhanced effectiveness in the transmission of research findings.
(iii) Increased learning and awareness (through school visits) of the opportunities, relevance and range career choices available through academia.
(iv) An increased range of career options to the staff employed through training in media, communication and business.