Risk Assessment: Predatory flies and parasitic wasps pose a low risk to Norwegian nature

Predatory flies and parasitic wasps are used to control dung flies in livestock production. The Norwegian Scientific Committee for Food and Environment (VKM) has assessed the potential negative environmental impacts of using these insects in Norwegian animal facilities.

The conclusion is that there is generally a low risk that any of the eight different insect species would cause harm to Norwegian biodiversity if released in stables and barns in Norway.

This assessment was commissioned by the Norwegian Environment Agency.

Background

Three species of flies, commonly referred to as dung flies, cause problems in Norwegian livestock production because they irritate animals, contaminate feed, and spread disease. As a result, they negatively affect both animal health and welfare.

These flies can be controlled using chemical and mechanical methods, but biological control is often also needed to keep their populations at an acceptable level. The Norwegian Environment Agency has received several applications for the import and release of both predatory flies and parasitic wasps for use in barns and stables.

Based on these applications, the Agency requested an assessment of which species are suitable for use in Norway and what risks their import and release might pose to biodiversity. In particular, the Agency wanted to know whether the species could establish populations in Norway under current climatic conditions and how climate change might affect the likelihood of establishment.

VKM's assessment

VKM investigated which species are currently used internationally and identified a total of eight species that may be relevant for use in Norway. These include one species of predatory fly, six species of parasitic wasps, and one beetle species; the latter primarily used in poultry production facilities.

VKM assessed whether each species could establish itself in Norwegian nature if individuals were to escape from production facilities.

“Several of the species are already present in Norway. However, it is unclear whether they are actually capable of surviving outdoors,” says Brett Sandercock, scientific coordinator of the assessment.

VKM also reviewed the available scientific literature and assessed the potential negative effects that the species could have should they establish themselves in Norwegian ecosystems. Five factors with the potential to negatively affect biodiversity were identified, and risk assessments were conducted for each:

• Predation on native species

• Competition with native species

• Parasitism of native species

• Hybridization with native species

• Transmission of diseases

In addition, VKM assessed cumulative ecosystem effects if several species were to establish simultaneously. Possible risk mitigation measures were also evaluated.

Results

VKM concludes that most of the species are unlikely to establish themselves in Norwegian nature because they require specific human-made habitats to survive. The assessment also finds a low risk associated with competition, hybridisation, and disease transmission for all evaluated species. For the predatory fly and the beetle species, both of which are predators, VKM concludes that there is also a low risk of negative impacts on Norwegian biodiversity through predation on native species.

No negative effects of the parasitic wasps on native species have been documented. However, the available knowledge base is limited. Therefore, the risk of negative impacts resulting from parasitism by the parasitic wasp species is assessed as moderate.

Should several species, particularly parasitic wasps, be established at the same time, VKM estimates a moderate risk of additive or synergistic effects on native species.

“These species are used on a large scale in other countries, and no specific cases of negative impacts have been documented elsewhere,” says Sandercock.

If the species are approved for import and use in livestock production, they would need to be released annually to maintain control of dung fly populations.

The risk assessment has been approved by VKM's Panel on Biodiversity.

VKM provides independent scientific assessments of issues relevant to the environment and the safety of food. VKM does not provide policy recommendations or decide how risks should be managed but may evaluate the consequences of different management options. It is therefore up to the commissioning authorities to determine which risk-reducing measures identified and assessed by VKM should be implemented.