Stem tissue mass density is linked to growth and resistance to a stem‐boring insect in Alternanthera philoxeroides

Abstract

AbstractTo investigate how stem anatomical structure is linked to growth and resistance to stem‐boring insects in a herbaceous species, six populations of alligatorweed (Alternanthera philoxeroides) were grown in a common garden. Stem growth rate (GR) of A. philoxeroides and pupation rate as an estimate of resistance to a stem‐boring insect (Agasicles hygrophila) were quantified. Stem tissue mass density (TMD) was measured and stem anatomical traits were analysed on cross‐sectional areas (CSA). Stem TMD was positively correlated with resistance (i.e. negatively correlated with pupation rate) and negatively correlated with GR. Stem cortex CSA (%) and vascular bundle (VB) density (no./mm2) were positively related to stem TMD and negatively related to pupation rate. The GR was positively related to VB CSA (%) and negatively related to VB density. These results suggest that stem TMD, which results from a high fraction in cortex CSA and high VB density, is a key determinant of resistance to a stem‐boring specialist in A. philoxeroides. The high resistance of plants with higher stem TMD may partially impose a cost to plant growth.