Sterile insect method to regulate rising world invasion of a Drosophilid fruit fly

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The Spotted Wing Drosophila (SWD), Drosophila suzukii, flies between rows of crops in a greenhouse and lands on flowering berries that attack the fresh produce and cause irreparable damage. Unlike other Drosophilidae, which live on harvested and decaying fruits, SWD has a preference for small fruits – blueberries, strawberries, and raspberries – and stone fruits such as cherries in open fields and in narrow greenhouses. SWD is a pest native to Southeast Asia and has landed across Europe, America and most recently in parts of Africa. Financial losses related to the stubborn pest infestation could reach millions of dollars annually – more than $ 500 million in the United States alone, according to a study published in Insects magazine.

The IAEA, in collaboration with the Food and Agriculture Organization of the United Nations (FAO), has the expertise and historical success in implementing sterile insect technology (SIT) to suppress or eradicate insect pests such as the Mediterranean fruit fly, screw worm flies, tsetse flies and various moths. Given the threat to fruit production from SWD around the world, several countries turned to the FAO and IAEA to assess the potential of SIT to suppress SWD in limited production systems such as greenhouses.

“To date, no environmentally friendly treatments have been developed to suppress this pest,” said Gustavo Taret of the Argentine Institute for Agricultural Health and Quality. “SIT would be the only environmentally friendly control method that enables use in greenhouses, reduces the use of insecticides and protects beneficial insects in the fight against other pests.”

How is the SIT package developed?
The first import of an SWD colony came from Italy in 2015 at the FAO / IAEA Laboratory for Insect Pest Control (IPCL) in Seibersdorf, Austria. Since then, the laboratory has investigated the radiation biology of the SWD, ie the effect of ionizing radiation on the induction of sterility. “For a new species, we need to evaluate different radiation doses from low to high to determine which radiation dose induces near 100 percent sterility,” said Carlos Caceres, a research entomologist on the joint FAO / IAEA program in nuclear food and agriculture.

To encourage the mass production of fruit flies for research purposes, scientists have developed egging systems and cages for adults. In the case of SWD, the developed egging or egg-laying system consists of plastic containers with holes that allow females to lay eggs. “The egg-laying system is a plate that consists of a fine mesh covering with wax. The females are attracted to a certain color of the egg-laying panel, ”explained Caceres. “Women lay eggs – or lay eggs – through the plate, then the eggs are collected on the outside of the cage.” Scientists have found that SWDs are attracted to black fields, which maximizes the number of eggs collected.

Once the eggs hatch into larvae, they are fed a diet of carrot powder, sugar, yeast, and water. Within a few days, the larvae transform into pupae. Once the pupae are ripe, they are collected and irradiated, rendering them sterile. After irradiation, the pupae are placed in holding cages in which sterile adult flies emerge. “The holding cages consist of an aluminum frame that is covered with a fine synthetic mesh. The cage has a supply of sugar and yeast as a source of nutrients and a water-soaked sponge to keep the flies hydrated, ”said Caceres. A cage measures 50 cm x 50 cm x 50 cm.

After three days in the holding cages, the adult flies become sexually mature and can be released in the target area to mate with fertile females, resulting in no offspring. This will consequently lead to a decline in the wild population with each generation.

Status of the SIT for SWD
Mass rearing protocols have been established for SWD, and handling and release protocols to ensure that the adult flies arrive healthy and competitive in the field are currently under review. “Stable and sufficient production of sterile insects is required in order to be able to conduct assessments in confined spaces or in greenhouses and to adjust the release rates and frequencies,” said Taret. So far, pilot tests have been carried out in greenhouses in Argentina, which produce 50,000 to 100,000 fruit flies per week. An additional pilot test is expected to be carried out in France this year.

The results of these pilot tests will enable the integration of SIT to control the SWD in the affected countries. “The basic technology for the SIT for SWD pilot test is in place, which would require about 2 million flies to be released per week in certain areas. However, adoption and use will depend on the phytosanitary authorities and fruit industry decision makers,” said Caceres.

The SIT package for SWD is expected to be completed in 2023. “The SIT can be integrated with other control methods, reducing crop losses, pesticide residues in food and the risk to workers,” said Caceres.

For more informations:
International Atomic Energy Agency
www.iaea.org

Mazzi D., Bravin E., Meraner M., Finger R., Kuske S. Economic effects of the introduction and establishment of Drosophila suzukii on sweet cherry production in Switzerland. Insects. 2017; 8 (1): Published 18, 2017 Feb 8. doi: 10.3390 / insects8010018