A bias-controlled statistical procedure to highlight host-plant preferences and the resulting prevalences in phytophagous insects: illustrative case study with leaf-miners on Lamiaceae

Abstract

Summary. Quantitative, rigorously derived and statistically validated information regarding the relative preferences/relative prevalences of phytophagous insects for/upon their different host plant species is too rarely made available in the literature, at least for wild host plant species, which are usually lacking economic interest. This seems likely to be due (i) in part to the usual lack of field samplings sufficiently wide (both numerically and spatially) to ensure the statistical significance of results; and (ii) to the current unavailability of a dedicated procedure for appropriately dealing with the unavoidable sources of biases affecting raw field data. Accordingly, a new methodological approach is proposed to overcome both kinds of difficulties, involving in particular: a procedure of evaluation of the relative preferences for hosts and relative prevalences on hosts, making them insensitive to the biases inevitably linked to the unavoidable large disparities among the respective abundances of the focused phytophagous insects on the one hand, and to the hardly controllable heterogeneities in sampling intensities of the different host plant species, on the other hand; an appropriately modified version of the standard Chi-2 testing procedure, applied to control the degree of statistical significance of the estimations of relative preferences and prevalences. The practical implementation of this newly derived approach is illustrated with a case study, dealing with leaf-mining insects upon host plant species belonging to Lamiaceae. From a purely descriptive point of view, more or less strong discrepancies turn out to single out the relative preference profiles, as well as the relative prevalence profiles of 10 leaf miners for four host-plant species (despite the relative phenotypic homogeneity of hosts within Lamiaceae). Highlighted, at a more speculative level, is the significant role played by phylogenetic affinities (between the exploiting species as well as between the exploited species) upon the arrangement of the food web that connects them.