Submitted to: Plant Species Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/29/2010
Publication Date: 1/1/2011
Citation: Pan, X., Jia, X., Zeng, J., Sosa, A.J., Li, B., Chen, J. 2011. Stem tissue mass density is linked to growth and resistance to a stem-boring insect in Alternanthera philoxeroides. Plant Species Biology. 26:58-65. Interpretive Summary: On this work we wanted to investigate the effect of anatomical structure of an invasive plant and its relation to its specialized insect. For that purpose we use alligator weed, an aquatic and terrestrial weed, and a flea beetle whose larvae bore the plant stem. This flea beetle is widely used as biological control of this weed, with ambiguous results, from tremendous success in aquatic situations to poor control in terrestrial ones. On a common garden experiment we measured growth rate of the plant and anatomical features (stem thickness, vascular bundle density) and its correlation with insect performance in six different populations of alligator weed. We found that thick plants seem to be resistant to this insect, pupation rate was the lowest. Moreover, this kind of plant had the lowest growth rate. This would imply that plants with low growth rate invest in producing tough stems to resist the attack of the insect, and that different populations of alligator weed have different levels of resistance to the insects.
Technical Abstract: To 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 analyzed 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.