ABSTRACT
356Exposure to ionizing radiation is currently the method of choice for rendering insects reproductively sterile for area-wide integrated pest management (AW-IPM) programmes that integrate the sterile insect technique (SIT). Gamma radiation from isotopic sources (mainly cobalt-60 or decreasingly caesium-137) is commonly used, but high-energy electrons and X-rays are other practical options. Recently, the development of self-contained low-energy X-ray irradiators for insect sterilization is being encouraged because they only require access to electricity and cooling water, and avoid the complex and costly shipment of radioactive sources across international borders. Insect irradiation is safe and reliable when established safety and quality-assurance guidelines are followed. The key processing parameter is absorbed dose, which must be tightly controlled to ensure that treated insects are sufficiently sterile in their reproductive cells and yet able to compete for mates with wild insects. To that end, accurate dosimetry (measurement of absorbed dose) is critical. Data from more than 5300 studies on irradiation since the 1950s, covering more than 360 arthropod species (IDIDAS database), indicate that the dose needed for sterilization of arthropods varies from less than 5 Gy for the acridid Schi stocerca gregaria (ForskM) to 400 Gy or more for some lyonetiid, noctuid, and pyralid moths. Factors such as oxygen level, insect age and stage during irradiation, and many others, influence both the absorbed dose required for sterilization and the viability of irradiated insects. Consideration of these factors in the design of irradiation protocols can help to find a balance between the sterility and competitiveness of insects produced for programmes that release sterile insects. Some programmes prefer to apply “precautionary” radiation doses to increase the security margin of sterilization, but this overdosing often lowers competitiveness to the point where the overall induced sterility in the wild population is reduced significantly.
