COLONISATION, DOMESTICATION AND POPULATION CONTROL IN PEST INSECTS

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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.