Publisher Summary This chapter describes sterile insect techniques (SIT). It is a biologically based method for the control of key insect pests. Wild female insects inseminated by released, radiation-sterilized males do not reproduce, and repeated releases of the sterilized insects lead to a reduction in pest population numbers. Effective control using sterile insects is achieved when they are used systematically as part of area-wide integrated pest management (AW-IPM) programs. SIT is species-specific, nonpolluting, and resistance-free. Since the original concept was developed in the United States in the 1940s, SIT has been used successfully for screwworm flies, tsetse flies, fruit flies, and moths. Technical progress in behavioral ecology, mass rearing, strain improvement, global information, positioning and monitoring systems, and aerial release, combined with economies of scale and a growing demand for pest-free and low-pesticide agricultural products in local and international trade, have increased the use of SIT in AW-IPM programs. These programs, by decreasing insecticide use, have also facilitated the use of biological control agents against secondary insect pests.

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Sterile Insect Technique

The sterile insect technique (SIT) depends greatly on the production of good quality sterile male insects that are released into target wild populations. Quality is assured through a system of bioassays of quality parameters that reflect the insect’s ability to survive, interact with its environment, and locate, mate and fertilize females of the target population. The system was developed by compartmentalizing the essential survival and mating behaviours of the species involved, and then developing a series of tests to confirm that these behavioural traits are present in the mass-reared insects. The system also has a feedback loop to correct problems in the production portion of the system before they become evident. Nevertheless, regular implementation of field or field-cage tests under semi-natural conditions, where sterile males have to compete with wild males for wild females, is required to provide the ultimate assurance that the sterile insects have the ability to fulfil their mission after release.

Sterile Insect Quality

Exposure 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 (cobalt-60 or caesium-137) is most often used, but high-energy electrons and X-rays are other practical options. 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. Irradiation data generated since the 1950s, covering over 300 arthropod species, indicate that the dose needed for sterilization of arthropods varies from less than 5 Gy for blaberid cockroaches to 300 Gy or more for some arctiid and pyralid moths. Factors such as oxygen level, and 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. Many programmes 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.

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Sterilizing Insects with Ionizing Radiation

In principle, the sterile insect technique (SIT) is applicable to controlling a wide variety of insect pests, but biological factors, interacting with socio-economic and political forces, restrict its practical use to a narrower set of pest species and situations. This chapter reviews how the biology and ecology of a given pest affect the feasibility and logistics of developing and using the SIT against that pest insect. The subjects of pest abundance, distribution, and population dynamics are discussed in relation to producing and delivering sufficient sterile insects to control target populations. Pest movement and distribution are considered as factors that influence the feasibility and design of SIT projects, including the need for population- or area-wide management approaches. Biological characteristics, that affect the ability of sterile insects to interact with wild populations, are presented, including the nature of mating systems of pests, behavioural and physiological consequences of mass production and sterilization, and mechanisms that males use to block a female’s acquisition and/or use of sperm from other males. An adequate knowledge of the biology of the pest species and potential target populations is needed, both for making sound decisions on whether integration of the SIT into an area-wide integrated pest management (AWIPM) programme is appropriate, and for the efficient and effective application of the technique.

Biological Basis of the Sterile Insect Technique

The purpose of the International Database on Insect Disinfestation and Sterilization (IDIDAS: http://www-ididas.iaea.org/ididas/) website is to collect and share information about radiation doses for disinfestation and reproductive sterilization of arthropods and to perform a comparative analysis and quality assurance check on existing data. IDIDAS was developed based on a literature review and analysis of >2,750 references, published during the past five decades. In total, 309 species of arthropods, mostly of economic importance, from 196 genera, 84 families, 9 insect orders, and 2 arachnid orders, have been subjected to irradiation studies for purposes of (1) research, such as sperm precedence determination and parasitoid-host interaction studies, (2) disinfestation for quarantine or phytosanitary purposes or (3) different pest control applications, including the sterile insect technique (SIT) and biological control programs. Sensitivity to radiation among families, and in particular orders, va...

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Fifty Years of Radiation Biology in Entomology: Lessons Learned from IDIDAS

Male and female codling moths, Cydia pomonella (L.), were treated with increasing doses of gamma radiation, and the moths were either inbred or outcrossed with fertile counterparts. Fecundity of untreated females mated with treated males declined slowly with increasing doses of radiation. However, fecundity of treated females declined almost linearly with dose at ≈22% per 100 Gy. The minimum dose at which treated females were found to be 100% sterile when mated to untreated males was 100 Gy. This dose was much lower than previously suggested. Fertility of treated males declined almost linearly to approach 0 near 400 Gy. Inherited effects resulting from irradiation of P1 males at selected doses were recorded for the F1 generation. As the dose of radiation increased, F1 fecundity and fertility decreased, mortality increased, and the F1 sex ratio shifted in favor of male progeny. The effect of releasing partially sterile codling moth males and fully sterile females at a 10:1 overflooding ratio in conjunction with untreated codling moths was examined in field cages each containing a single apple tree. Fruit damage was significantly reduced in all treatments when compared with controls, and production of F1 progeny were seen in cages containing moths treated with 100 Gy.

Inherited sterility in codling moth (Lepidoptera: Tortricidae): effect of substerilizing doses of radiation on insect fecundity, fertility, and control.

Environ. Entomol. 28(4): 669-674 (1999) In release-recapture tests conducted in apple orchards in Oroville, WA, a significant relationship was found between the dose of gamma radiation used to treat adult male codling moths, Cydia pomonella (L.), and the number of males recaptured in virgin female-baited sticky traps. Males treated with 100 Gy responded to calling virgin females in larger percentages than those treated with 200 and 250 Gy. However, the percentage of untreated (released) males captured was lower than the percentage of 100 Gy-treated males captured; a possible explanation for this is that untreated males were moving farther away and were less likely to be near the female-baited traps for recapture. Recapture was highest at days 4 and 5 after release, and significantly more males of all treatments were recaptured when dusk temperatures were at or above 16°C. Radiation also had a negative impact on codling moth mating competitiveness in the field. In mating table experiments, successful matings decreased as the dose of radiation increased. Untreated males were the most competitive among released codling moths.

S. Bloem

Papers

Inherited sterility in codling moth (Lepidoptera: Tortricidae): effect of substerilizing doses of radiation on insect fecundity, fertility, and control.

Inherited sterility in codling moth (Lepidoptera : Tortricidae) : Effect of substerilizing doses of radiation on field competitiveness

Incorporation of diapause into codling moth mass rearing: production advantages and insect quality issues.