Biological control

Biological control involves the mass-production and release of natural enemies such as parasitoids and predators to control pest insects in an environmentally sound manner. Radiation is used to increase the applicability, cost-effectiveness and safety of rearing, shipping and deploying such natural enemies.

Augmentative biological control, involving the supplemental release of natural enemies of insect pests, can complement the sterile insect technique (SIT) in area-wide integrated pest management programmes. While under the SIT sterile males are predominantly released at the adult stage, many of their natural enemies attack them in immature stages. This means that using both control techniques at the same time can often produce mutually supporting enhanced results. Additionally, by-products from insect mass rearing facilities can be used in production processes related to augmentative biological control programmes.

Ionizing radiation, using gamma rays and X-rays, can alleviate a number of important constraints to the use of augmentative biological control, such as reducing the cost of production systems for biological control agents, preventing the emergence of adult pest insects from hosts used to mass rear parasitoids – parasites that kill their insect hosts – and assuring the sterility of accompanying pest organisms during their shipment. It is also effectively applied to eliminate the risk of shipping fertile host or prey pests, or other hitchhiking pests.

Jointly with the FAO, the IAEA assists Member States in developing and adopting nuclear-based technologies for optimising such biological insect pest management practices, supporting the intensification of crop production and the preservation of natural resources.

Applying biological control and SIT on the ground

The combined use of parasitoids and the SIT has been applied in several states in Mexico, to control populations of the Mexican fruit fly and the West Indies fruit fly. Release of both agents are carried out simultaneously, targeting with parasitoids the fruit fly larvae infesting fruit and the wild adults with sterilized released adults to prevent the wild population from reproducing. The parasitoids are mass-reared in fruit fly larvae that have been irradiated to prevent the emergence of adult flies from larvae that were not parasitized.

In Costa Rica, a similar application is being used for parasitoids of the stable fly. The parasitoids have been successfully reared in sterilized larvae of this fly, which is its natural host. This fly is a pest of economic significance for the livestock industry in Costa Rica and many other IAEA Member States.

Other contributions of nuclear and isotopic techniques

Radiation can be used to sterilize non-native biological control agents, thereby reducing the risk of their introduction, as part of classical biological control, into new environments where they could potentially become pests of non-target organisms. Ionizing radiation is also a useful tool in studying physiological host-parasitoid interactions, such as host immune responses, by suppressing defensive reactions of natural or factitious (unnatural) hosts.

Additionally, ionizing radiation can be applied to semi- or completely sterilize hosts or prey for deployment in the field to monitor natural enemy populations or to increase the initial survival and build-up of natural or released biological control agents in advance of seasonal pest population growth.