Biological controls: bud-galling wasp assessed

Establishment of T. acaciaelongifoliaein Portugal would be likely because: host plants are present; the organism A living thing such as humans, animals, plants and microbes (e.g. bacteria, viruses) has been successfully established in South Africa; and environmental conditions in the proposed release area are similar to those in its native home of Australia. However, there is some uncertainty Scientific concept used in risk assessment to describe all types of limitations in available knowledge at the time an assessment is conducted, with the agreed resources, that affect the probability of possible outcomes to the assessment as there is no record of the wasp having ever established in the northern hemisphere.

Once established, the wasp would have a “massive” effect on invasive A. longifolia, reducing the growth, reproductive potential and ultimately population Community of humans, animals or plants from the same species density of the plant, EFSA’s plant health experts concluded. It would also significantly reduce the negative effects of A. longifolia on biodiversity A term used to describe the variety of living organisms existing in a specific environment in the targeted area.

It is possible that the wasp could spread outside the target area through trade in ornamental A. longifolia and A. floribunda. However, these species are grown in a limited number of nurseries in Europe compared to acacia species which are not hosts of T. acaciaelongifoliae.

There would be little impact on populations of other invasive or ornamental acaciaspecies because of the wasp’s high degree of specificity – it survives and reproduces only in A. longifolia and the closely related A. floribunda – although there may be short-lived spill-overs to other species. One native wild species – the broom Cytisus striatus – and one ornamental species – Acacia retinodes – need to be further investigated because the currently available data on their host status for the wasp are inconclusive.

As with the release of other biological control agents, there would be no way of preventing the spread of T. acaciaelongifoliae to other areas. However, spread would be limited by a number of factors, such as the fragmented nature of host populations outside Portugal, and the fact that the female wasps die unless they find a host plant A plant on which a pest lives or by which it is nourished within three days of hatching.

EFSA was asked to carry out an assessment of the risk of establishment and spread of  T. acaciaelongifoliae in the EUafter Portugal informed the European Commission that it was considering using the organismto control the spread of A. longifolia in coastal sand dune areas. The wasp, which is native to Australia, was released intentionally in South Africa in 1982-1983 to control A. longifolia and has successfully established and spread there. Seed set on affected hosts has subsequently fallen by up to 95%.

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