Inherited sterility

Moth pests can be rendered sterile through high doses of radiation. However, much lower and less debilitating doses induce inherited sterility in the moths' offspring. Released males with inherited sterility suppress wild populations to a greater extent than an equal number of fully sterile males.

Similar to the sterile insect technique, inherited sterility involves the mass rearing and release of irradiated insects to ensure that when mating occurs in the field, a significant proportion of matings will involve a sterilized insect. The target insects are irradiated with gamma rays and X-rays, which induce inherited sterility. Research has shown that the offspring of those target insects are more sterile than their parental generation.

The technique is mainly used with Lepidopteran pests, an order of insects that includes moths and butterflies. Some of these pests have a high radio-resistance, which describes the level of ionizing radiation that organisms are able to withstand. Studies on the codling moth (Cydia pomonella) have shown that male moths treated with sub-sterilizing doses of radiation, which are then mated with virgin fertile females, will produce fewer offspring, most of whom will be completely sterile.Jointly with the FAO, the IAEA helps Member States develop and adopt nuclear-based technologies to optimise such agricultural insect pest management practices that support the intensification of crop production and the preservation of natural resources.

Using a genetic phenomenon for pest control

Attributes that are common to inherited sterility in Lepidoptera are that:

  • Male and female offspring are more sterile than the irradiated parental generation.
  • More male than female offspring is produced.
  • The development time is longer and sperm quality of the offspring is reduced.

The unique genetic phenomena responsible for inherited sterility in Lepidoptera and some other arthropods, as compared with full sterility, provide advantages for pest control. Lepidopteran females generally are more sensitive to radiation than are males of the same species. This allows the dose of radiation to be adjusted so that treated females are completely sterile and males are partially sterile. When these partially sterile males mate with wild females, the radiation-induced harmful effects are inherited by the next generation. At the same time, the lower dose of radiation used to induce sterility increases the quality and competitiveness of the released insects.

Field programmes releasing irradiated moths under an SIT or inherited sterility approach have been in operation since the 1960s. The pink bollworm, Pectinophora gossypiella, has been successfully contained since 1969 in cotton areas of the San Joaquin Valley in California and is being successfully targeted for eradication from cotton areas in the south-western USA and north-western Mexico. Since the early 1990's, the codling moth has been successfully suppressed in apple and pear production areas in the Okanagan Valley in British Columbia, Canada, and countries such as Argentina, Brazil and South Africa have plans or programmes against this pest. New Zealand eradicated outbreaks of the Australian painted apple moth, Teia anartoides. Mexico eliminated outbreaks of the cactus moth, Cactoblastis cactorum, and the USA contains its advance along the Gulf of Mexico coast. South Africa has a programme to suppress the false codling moth, Thaumatotibia leucotreta, in citrus orchards.

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