Not just a Citrus problem: The expanding threat of Scirtothrips aurantii and the importance of alternative host plants

Abstract: Scirtothrips aurantii is a polyphagous invasive pest of quarantine importance in
Europe, originally from South Africa. Its geographic range has been slowly expanding since its first introduction in Andalucia (Spain) in 2020 along both the Atlantic and Mediterranean coast of the Iberian peninsula. Initially a significant problem for protected berry crops, after reaching the citrus-growing belt of Spain it has also emerged as a key pest for citriculture. Feeding damage on young tissues and developing fruits can severely reduce plant vigour and
marketability across susceptible hosts. In Mediterranean systems, non-crop vegetation such as cover crops and surrounding spontaneous flora plays an increasingly important role in
conservation biological control. However, the establishment of S. aurantii introduces new
challenges for managing these vegetational components, particularly given the pest’s ability to exploit a plethora of hosts. After initial reports of this pest in the Valencia region in spring 2024, we initiated periodic surveys of more than 50 plant species present in citrus cover crops and adjacent natural habitats. Thrips communities were extracted using Berlese funnels and identified under a microscope. Our findings show that the suitability of non-crop plants as alternative hosts for S. aurantii varies markedly with plant family, species, and season. While most common plant species did not host the pest, several others, such as Rosaceae and Fabaceae shrubs, ornamental trees and perennials, served as seasonal reservoirs from late spring through autumn. This study provides foundational knowledge for developing ecologically based management strategies for S. aurantii through conservation biological control and cover crop management and offers insights relevant to protected horticulture systems in northern Europe, where the pest’s broad host range could pose significant risks if introduced.