Modelling the potential for the biological control of Alternanthera philoxeroides
Alternanthera philoxeroides (Amaranthaceae, EPPO A2 List) is an emergent aquatic plant that can be found growing in both aquatic and terrestrial habitats. The species originates from South America and it is invasive in Australia, the USA, New Zealand and numerous countries of Asia (e.g. India, Thailand). In the EPPO region it has a limited distribution and is only recorded in Italy, France, and Spain where it has recently been found in the northwest of the country. A. philoxeroides can have several negative impacts including outcompeting native plant species and negatively affecting ecosystem services. Globally, in regions where the species is invasive, classical biological control has been utilised as a management tool using the specialist insect Agasicles hygrophila (Coleoptera: Chrysomelidae). However, two factors limit the effectiveness of the biocontrol agent: temperature and plant ecotype (the terrestrial form lacks the hollow stem necessary for A. hygrophila to complete its lifecycle). A model was built that included growth parameters of A. philoxeroides along with population dynamics of A. hygrophila. Modelling of climatic variables was based on the climate where the species is present in Spain. The model simulation period was 10 years. Without biocontrol, the model predicts that the population of A. philoxeroides will increase to 600 % of its initial surface area after 10 years. With the introduction of the biocontrol agent, the model predicts that control of A. philoxeroides is possible, if several releases of the biocontrol agent are made over time. The model also predicts that the optimal time of year for releasing the biocontrol agent is April as before this period, eggs may die due to low temperatures. The authors considered that the proposed model is a dynamic tool which can be adjusted to different contexts and in particular to different local management specificities. Hence, this approach could be used to guide eradication efforts of new invasive species, to improve the applicability of biocontrol, and to support decision-making by testing several alternative management scenarios.
Portela R, Vicente JR, Roiloa SR, Cabral JA (2020) A dynamic model-based framework to test the effectiveness of biocontrol targeting a new plant invader– the case of Alternanthera philoxeroides in the Iberian Peninsula. Journal of Environmental Management 264, 110349. https://doi.org/10.1016/j.jenvman.2020.110349