Ranking the host range of biological control agents with quantitative metrics of taxonomic specificity

• Published in: Biological control 2021-01, Vol.152, p.104427, Article 104427
• Main Authors: Abram, Paul K., Labbe, Roselyne M., Mason, Peter G.
• Format: Article
• Language: English
• Subjects: Aleurotrachelus trachoides; Host range; Lobesia botrana; Non-target risk; PSV; Specificity index; STD
• ISSN: 1049-9644; 1090-2112
• DOI: 10.1016/j.biocontrol.2020.104427

[Display omitted] •The specificity of biological control agents is usually described qualitatively.•Quantitative metrics of taxonomic host range could be used to rank agent specificity.•We describe two such metrics and apply them to two case studies of pest insects.•We discuss guidelines for use of these metrics and their limitations. The need to prevent negative impacts of importation biological control on native biodiversity has made evaluating the specificity (host range) of natural enemies a central issue for the application of biological control programs against pest organisms. Thus, when there are a number of candidate species being considered for introduction as biological control agents against a particular target pest, it is important to compare their relative host ranges. These comparisons are usually made informally using categorical terminology (e.g., generalist, specialist, oligophagous). However, relative differences in natural enemy host range are better expressed quantitatively, with both ecological (how many host species a natural enemy is capable of exploiting) and evolutionary (how the host species are related phylogenetically) components. We propose using two previously developed quantitative taxonomic and phylogenetic metrics (taxonomic host range – STD; phylogenetic species variability – PSV), in combination with the number of associated host species (host species richness), as heuristic tools to rank the relative host specificity of candidate biological control agents. We first show that although STD and PSV were developed independently, they are directly related mathematically and convey exactly the same information except on different numerical scales. We then apply the metrics to case studies regarding the host range of candidate biological control agents for: (i) an invasive whitefly in greenhouse crops, Aleurotrachelus trachoides (Hemiptera: Aleyrodidae), and (ii) an invasive pest of grapes, Lobesia botrana (Lepidoptera: Tortricidae). We also provide open source code to easily allow the calculation of these metrics for any natural enemy for which taxonomic host range information is available. Finally, we describe potential uses of these metrics in applied biological control as well as important caveats and limitations that require further theoretical work to address. We conclude that while these metrics should not be considered as absolute or infallible measurements of host range, their application should encourage biological co