Following a request from the European Commission, the EFSA Panel on Plant Health has delivered a scientific opinion on the evaluation of the pest risk analysis on Pomacea insularum, the island apple snail, prepared by the Spanish Ministry of Environment and Rural and Marine Affairs.
For the evaluation of the Spanish PRA the Panel followed the EFSA guidance on evaluation of pest risk assessments and risk management options prepared to justify requests for phytosanitary measures under Council Directive 2000/29/EC (EFSA, 2009) and the guidance document on the harmonised framework for risk assessment (EFSA Panel on Plant Health (PLH), 2010a). The Panel has developed, for the purpose of this opinion, rating descriptors for the different components of the risk (entry, establishment, spread and potential consequences) and for the uncertainties. This is to provide transparent and clear justification when a rating different from that in the PRA is given. With regard to the risk management options, the Panel reviewed the document in terms of whether the options have been identified and evaluated for their effectiveness in reducing the risk.
The Panel considers the Spanish PRA to be clear and to provide appropriate supporting evidence.
However, unlike the Spanish PRA the Panel considers that it is scientifically more correct to include both species, P. insularum (d´Orbigny, 1835) and P. canaliculata (Lamarck, 1819), in the assessment. These two species are almost indistinguishable and have very similar impacts on invaded ecosystems.
Moreover the Panel highlights additional limitations of the Spanish PRA:
- The risks for habitats other than rice fields and natural wetlands, such as slow-flowing rivers and small water bodies, are not considered. These ecosystems may serve as reservoirs for the snails and as an infrastructure for spread. Understanding the movements of snail populations between rice fields and other aquatic ecosystems requires proper consideration of their population dynamics in natural environments.
- The contribution of the spread of eggs as a natural means of dispersal, particularly through slow-flowing rivers and the network of artificial canals, is insufficiently discussed.
- The environmental impact assessment is presented in very general terms, although detailed available information shows that environmental consequences in the risk assessment area could be massive under suitable environmental conditions. In particular, information is lacking on how snail population density could be the key variable in predicting the environmental consequences.
- The estimates for the potentially endangered area are probably too limited with regard to the climatic suitability of and host plant availability in the PRA area.
Based on the evidence provided in the pest categorization stage of the Spanish PRA, as well as on additional information collected, the Panel confirms that a full pest risk assessment for the canaliculata complex is justified.
The Panel finds the information on the consequences to cultivated and managed plants, as described in the Spanish PRA, adequate but believes that it omits essential information about the environmental consequences, and the Panel considers it insufficient to state that infestation by P. insularum in wetland areas could be very detrimental to the conservation of such areas without providing any predictions or scenarios. Studies on the effects of P. canaliculata on natural wetland ecosystems show strong negative and fairly predictable impacts on biodiversity, ecosystem functioning and ecosystem services.
To evaluate the probability of establishment of the organism in the risk assessment area, the Panel performed a simple climate-matching analysis. The results indicate that climate will not prevent further establishment and spread of Pomacea spp. in the risk assessment area. However, considerable uncertainty remains regarding the northern and altitudinal climatic limits for the establishment of the species. Other abiotic or biotic factors may limit the potential area of establishment to a narrower extent than the area determined by the climatic conditions of the risk assessment area alone. After an evaluation of the published information about the wide host plant range of Pomacea spp., the Panel concludes that establishment and spread will not be limited by food resources in the PRA area. The Spanish PRA concludes that the endangered area corresponds with the rice-growing areas and natural wetlands along the EU’s Mediterranean coast, but results from the climate-matching analysis conducted by the Panel indicate that climate is not a limiting factor for spread and further establishment in the PRA area. Large areas of Europe have climatic conditions very similar to those in the areas of native distribution of Pomacea spp. snails. Furthermore, the Panel concludes that suitable host plants are available within these zones. As the snails are currently intentionally imported into the PRA area, they are associated with the pathways mentioned in the Spanish PRA, and survival before, during and after transport is highly probable owing to the provision of suitable conditions during intentional transport. The Spanish PRA describes several ways in which the snails are transferred to a suitable host (intentional release, escape from outdoor aquaria and water gardens, and escape from outdoor aquaria rearing snails), but the Panel would like to add that specific characteristics of the snail (survival periods of several months during dry periods, survival on many different host plants) may enhance the probability of its transfer.
The Panel agrees with the Spanish PRA that the potential consequences of the organism for cultivated and managed plants are major with low uncertainty, but the Panel considers the effects on the environment to be massive instead of major with low uncertainty because of the very serious environmental effects observed in areas invaded previously. The Panel agrees with the Spanish PRA that the probability of establishment of the organism in the risk assessment area is very likely with low uncertainty. However, owing to the lack of biological data on the organism, the Panel considers the uncertainty high regarding the northernmost limit of distribution in the PRA area. The Panel also agrees with the rating for spread given in the Spanish PRA, which is “likely”. The Panel agrees with the conclusion in the PRA that the import of P. insularum for the pet/aquarium trade or for weed control is more relevant than the other pathways listed. However, the Panel considers the rating for the probability of entry of the organism into the Spanish PRA to be too low. The Panel ranks the probability of entry as high, rather than moderately likely, as in the Spanish PRA, based on the fact that the organism can currently be freely imported and released in the PRA area.
The Panel agrees with the final conclusion reached in the Spanish PRA regarding the introduction and spread of the organism in the PRA: likely with low levels of uncertainty.
Risk reduction options are well reviewed and described in the Spanish PRA. As pointed out in the PRA, no single risk reduction method is sufficient to halt the introduction and spread of Pomacea spp. snails in the PRA area, but legislation is intended to reduce the probability of entry, and the many risk reductions options listed will help to reduce the probability of spread within the PRA area. If legislation is considered, the Panel suggests that it should target the entire canaliculata complex, and not only P. insularum, as misidentification of species is likely and further import of P. insularum and P. canaliculata cannot be excluded. Likewise, if a ban on both breeding and trade of the organism is considered, the Panel suggests that such a ban should include the whole canaliculata complex. The Panel found that the risk reduction options listed in the Spanish PRA cover those that are used in integrated pest management of Pomacea spp. elsewhere in the world. The Panel identified some weak points that need further attention: (i) the effects on non-target organisms as a result of the mentioned risk reduction options are only superficially touched upon and need to be further developed; (ii) more attention should be given to early detection and control of the snail’s eggs to prevent further dispersal; and (iii) the issue of provision of information deserves more attention as knowledge of the snail problem at the level of stakeholders, environmental management professionals and the public is crucial to allow early detection, to prevent further spread and to generate rapid reports of its presence to the managing authorities.
The Panel recognises that the evaluation of the impact of Pomacea spp. on animal and human health falls outside its remit; however, it wishes to note that, owing to the seriousness of this potential impact, it should be assessed by the competent authorities.
As the Panel found essential information about the environmental consequences in the Spanish PRA lacking and available studies on the effects of Pomacea spp. on natural wetland ecosystems show strong negative and fairly predictable impacts on biodiversity, ecosystem functioning and ecosystem services, the Panel recommends that an appropriate environmental risk assessment is conducted according to the recently developed EFA PLH Guidance Document (EFSA Panel on Plant Health (PLH), 2011a: Guidance on the environmental risk assessment of plant pests) to give a better estimate of the potential effects of apple snails on biodiversity and ecosystem processes in the PRA area.
Further, the Panel recommends a detailed climatic study, which should not only give a clearer idea of the extent (particularly the northern limits) of the wetlands that are vulnerable but should also help to clarify the number of possible generations of Pomacea spp., their population density and the level of economic and environmental impacts that can be expected.
Because of the grave concern for rice production and wetland ecology in the EU, the Panel recommends to target research for the study of the biology of Pomacea spp. snails in the Ebro Delta to reduce important uncertainties highlighted in the PRA.
Finally, the Panel recommends exploring and testing new control techniques to improve those already used, because no single currently used risk reduction option has the potential to eradicate the snail from the area of infestation at present. Moreover, many of the currently used risk reduction options have negative effects on non-target organisms and the associated crop and natural wetland environment.