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ARS Home Office of International Research Engagement and Cooperation France and Greece EBCL





- Research Highlights
- Allium Leaf Miner Project
- Asian Longhorned Tick
- Bagrada Project
- Cattle Fever Tick Project
- Diamondback Moth Project
- French Broom Project
- Olive Fruit Fly Project
- Tree of Heaven Project
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Diamondback Moth Project Research leaders: Gaylord Desurmont, Marie-Claude Bon, Javid Kashefi **Presentation & Context** The Diamondback moth *Plutella xylostella* (DBM) is a major pest of cultivated crucifers, particularly *Brassica* crops (cabbage, brussels sprouts, broccoli, kale, canola...). This true cosmopolitan pest causes problems for Brassica growers worldwide, with an estimated annual cost of 4-5 billion $US for growers. Chemical control has been the main management strategy to regulate DBM populations, but the pest has developed resistance to the main classes of synthetic insecticides that are used for its control. Resistance problems have led to an increase in the quantities of insecticides applied, which in turn have given rise to even higher insecticide resistance, higher levels of crop damage, and increased concerns about pesticide residues and their impact on human health and the environment. The limitations of chemical control have urged growers to find alternative pest control solutions, including biological control and integrated pest management. *Young diamondback moth larvae feeding on a mustard leaf* *Collection of diamondback moth larvae and pupae in an organic cabbage field in the south of France* Biological control relies on the natural regulation of pest populations by their natural enemies. These natural enemies can be generalist predators such as ladybeetles, or parasitoids, which are in general more specialized, or even entomopathogens (bacteria, fungi, nematodes or viruses specific to insects). Classical biological control programs rely on the introduction of natural enemies originating from the native range of the target pest to its invasive range in order to re-establish a natural equilibrium that was lost in the invasion process. DBM is a particularly promising target for classical biological control because many natural enemies are known to attack its different life stages worldwide. However, several challenges remain. First, there is no clear consensus on the origin of DBM. Populations of DBM from different geographical areas have considerably mixed over time and adapted to their local environments, making the extent of the native range of this pest difficult to delimit. Secondly, the existence of many natural enemies worldwide does not guarantee that one of them could be introduced and used as a biological control agent in the USA. Prospective biological control agents must meet several critical conditions to be considered adequate for introduction, including: 1) high impact on the target pest, 2) high specificity (the agent must not impact non-target species), and 3) high level of adaptation to the environmental conditions of its area of introduction. Research Components In 2022, EBCL USDA ARS started a research project on the biological control of DBM in California. This project is a collaboration between the Californian Department of Food and Agriculture biological control program (CDFA),University of California, Riverside (UC Riverside), University of California, Davis (UC Davis), USDA-ARSCrop Improvement and Protection Research Unit Salinas, and Driscoll's Inc. The EBCL participation has the following objectives: To genetically characterize DBM populations and their natural enemies in different parts of Europe and Africa.
To select a population of *Diadegma semiclausum* (Hymenoptera: Braconidae, a parasitic wasp that attacks DBM larvae) that is well adapted to the current Californian DBM populations. The parasitoid *D. semiclausum* is a particularly promising natural enemy of DBM because of its high impact on DBM populations and high level of specificity. It has been successfully introduced and used as a biocontrol agent in several areas of the world. In the USA, another closely related species of *D. semiclausum*, *Diadegma insulare* is one of the main natural enemies of DBM. /ARSUserFiles/oirp/EBCL/DBM3a.jpgDiadegma semiclausum,*a natural enemy of diamondback moth* As of January 2023, a total of eight species of parasitoids of DBM have been collected by EBCL, mainly from cabbage fields located in France and Greece. The impact of these parasitoids on local DBM populations was high, exceeding 50% in some locations. A rearing of six populations of DBM (origins: France, the Netherlands, Greece, and the USA (x3)) and two populations of the parasitoid *D. semiclausum* (origins: The Netherlands and Greece) were initiated and are currently maintained at EBCL. In 2023, these populations of *D. semiclausum* are being evaluated against their original DBM population and DBM populations from California, including populations that show insecticide resistance, under quarantine conditions. Several parameters of parasitoid performance will be measured to select the most suitable *D. semiclausum* population for use in California. Additional experiments will investigate the effects of host plant on parasitism success and the competitive interactions between *D. semiclausum* and *D. insulare*. *Device designed to collect diamondback moth eggs and facilitate rearing under laboratory conditions. A cabbage leaf is placed underneath a striated plastic cover.**The right picture is a close-up of the device showing the eggs being laid along the streaks of the plastic cover*. The full list of parasitoids of DBM collected by EBCL in 2022 is as follows: France -*Diadegma semiclausum* (Ichneumonidae) -*Diadegma fenestrale* (Ichneumonidae) -*Diadromus collaris* (Ichneumonidae) -*Cotesia vestalis* (Braconidae: Microgastrinae) -*Dolichogenidea sicaria* (Braconidae: Microgastrinae) -*Diolcogaster claritibia* (Braconidae: Microgastrinae) Greece -*Diadegma semiclausum* (Ichneumonidae) -*Oomyzus Sokolowski* (Chalcidoidea: Eulophidae) -*Dolichogenidea appellator* (Braconidae: Microgastrinae)  *Overview of the eight parasitoid species of Diamondback moth collected by EBCL USDA ARS in 2022, as well as two species of hyperparasitoids (right pictures)*


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