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A Special Issue Published on the Use of Symbiotic Bacteria to Enhance the Effectiveness and Efficiency of the Sterile Insect Technique

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Different sections of the alimentary tract in the head of a fruit fly. The colonies of symbiont bacteria species which contribute to regulate the physiology of the fruit fly typically congregate in this area. (Photo: Kala Bhandari, University of Adelaide.)

Insects are, in many ways, the dominant multicellular lifeform on land. They are successful across multiple ecosystems and maintain intricate and complex interactions with the other organisms in their habitats. Many of the interactions between insects and plants, and insects and vertebrates have been extensively studied, but the associations between insects and microorganisms, while pervasive and of paramount ecological and evolutionary importance, are only gradually being understood. Insects depend on symbiotic associations with a variety of microorganisms, which affect many aspects of the hosts’ biology and physiology including their nutrition, mating behaviours, immunities and reproductive success.

Tephritid fruit flies are no exception and maintain intricate interactions with multiple micro-organisms. It is these complex relationships that are being explored by the IAEA, in partnership with the Food and Agriculture Organization of the United Nations (FAO), to help develop sustainable methods to reduce the spread of these destructive insect species.

The sterile insect technique (SIT) has been effectively deployed to reduce fruit fly populations for over 60 years. SIT is a species-specific and environment-friendly technology which is often used as a component of area-wide integrated pest management (AW-IPM) programmes. Experience has shown that the efficiency of SIT can be hampered by the quality of the mass-reared and sterilised male insects, that must remain competitive with wild males on release, and the cost effectiveness of mass-rearing the billions of insects required for a sustainable operational project. Research efforts focussed on ways to improve these processes have recognised the symbiotic relationships between tephritids and particular species of bacteria as potential targets for improving the quality of the sterilized males and reducing costs of production,

This area of research has been further explored in an IAEA Coordinated Research Project (CRP) on the ‘Use of Symbiotic Bacteria to Reduce Mass-Rearing Costs and Increase Mating Success in Selected Fruit Pests in Support of SIT Application.’ The CRP was initiated in 2012 under the auspices of the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture with four main objectives: To determine the effect of radiation on the symbiotic communities in target species; to develop methods of using beneficial bacteria to replace costly ingredients in larval diets; to explore the use of symbionts as probiotics provided to adult sterile males before their release to significantly improve their performance; and, to harness symbiotic microorganisms as reproductive manipulators and determine their ability to suppress target populations.

The CRP has illustrated the utility of harnessing symbiotic associations towards the reproductive manipulation and suppression of target populations. Specifically, the effect of Wolbachia infection on Ceratitis capitata has been studied, revealing the practical potential for introducing this bacterium into mass reared and wild populations. In addition, the bacteria associated with most of the tephritid pests have been identified for the first time and the role of bacteria in mass rearing facilities has been elucidated for several key pest species.

The research studied and documented the effect of sterilizing radiation on the microbiota of several mass-reared species. The use of symbionts as probiotic supplements to improve larval rearing and adult quality was also studied in several species of Anastrepha, Bactrocera, and Ceratitis capitata.

All the major achievements of the CRP were published in a dedicated Special Issue, with 19 papers, in a Cross-Journal Supplement of BMC Microbiology and BMC Biotechnology. This Special Issue provides an important contribution to our knowledge on tephritid fruit flies and their symbionts, and the related potential for enhancing applied SIT technology in the field.

In addition, an online tool for calculating distribution of operational taxonomic units generated from new generation sequencing approaches has been developed. And a compilation of all the microorganisms identified before and during the CRP was produced and included in the final report of the CRP.

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