Considering biology when inferring range-limiting stress mechanisms for agricultural pests: a case study of the beet armyworm

Abstract

Reliable niche models are a cornerstone of pest risk analyses, informing biosecurity policies and the management of biological invasions. Because species can invade and establish in areas with climates that are different from those that are found in their native range, it is important to accurately capture the range-limiting mechanisms in models that project climate suitability. We examined a published niche model for the beet armyworm, Spodoptera exigua, to assess its suitability for bioeconomic analyses of its pest threat, and identified issues with the model that rendered it unreliable for this purpose. Consequently, we refitted the CLIMEX model, paying close attention to the biology underpinning the stress mechanisms. This highlighted the necessity of carefully considering how the different stress mechanisms operate, and to select mechanisms which align with knowledge on the species’ biology. We also identified the important role of irrigation in modifying habitat suitability. The refitted model accords with both distribution data and our understanding of the biology of this species, including its seasonal range dynamics. The new model identifies establishment risks to South America, Africa, the Middle East and Asia, and highlights that under current climate, Europe is only climatically suitable during warm seasons when crops are available. The modelling exercise reinforced the importance of understanding the meaning of a location record (e.g. persistent versus ephemeral populations) and of carefully exploring the role of habitat-modifying factors, such as irrigation, in allowing species to persist in otherwise inclement localities.