The Iridoid Glucoside, Antirrhinoside, from Antirrhinum majus L. has Differential Effects on Two Generalist Insect Herbivores

Abstract

The iridoid glucoside, antirrhinoside, is constitutively distributed throughout Antirrhinum majus L. in a manner consistent with its possible role as an allelochemical, but there is no evidence that it has a defensive function with respect to insect herbivory. To address this question, two generalist herbivores, Lymantria dispar L. (gypsy moth) and Trichoplusia ni Hübner (cabbage looper) were chosen for feeding trials on excised whole leaves of A. majus and in artificial diet assays. In leaf excision feeding trials, fourth instar gypsy moth rejected, without sampling, the leaves of A. majus regardless of what node the leaf was excised from. In contrast, fourth instar cabbage looper readily fed on the excised leaves, and antirrhinoside was not found in their bodies or feces (frass) as determined by thin layer and high-pressure liquid chromatography. In the leaf and diet assays, a second major leaf iridoid in A. majus, antirrhide, was found in both cabbage looper and gypsy moth frass. In diet feeding assays, the growth of gypsy moth and cabbage looper were not inhibited by methanol extracts, iridoid fractions, or pure antirrhinoside at concentrations of 0.6% in diet, but cabbage looper growth was enhanced. At an antirrhinoside concentration of 3.3% in diet, gypsy moth growth was reduced, whereas cabbage looper growth again increased significantly relative to the control. It is likely that antirrhinoside functions as defense against herbivory for one generalist insect herbivore but also, at low concentrations, enhances the growth of another.

Soil nitrogen availability and herbivore attack influence the chemical defenses of an invasive plant (Linaria dalmatica; Plantaginaceae)

“…Quantitative variation in allelochemicals is likely to influence plant interactions with both generalist and specialist herbivores. High iridoid glycosides concentrations can have a greater negative effect on the growth and performance of generalist insect herbivores compared to low concentrations (e.g., Bowers and Puttick 1989;Biere et al 2004;Beninger et al 2008). In contrast, iridoid glycosides are often positively associated with the preference and performance of specialist insect herbivores (e.g., Bowers 1984;Pereyra and Bowers 1988;Bowers and Puttick 1989; Klockars et al 1993;Nieminen et al 2003;Harvey et al 2005;Prudic et al 2005;Saastamoinen et al 2007;Reudler Talsma et al 2008).…”

“…This species produces iridoid glycosides (Handjieva et al 1993;Franzyk et al 1999), which are a group of monoterpene-derived secondary metabolites found in more than 50 plant families (El-Naggar and Beal 1980;Stermitz 1990, 1991). Iridoid glycosides have been shown to act as chemical defenses against generalist insect herbivores and fungal pathogens as well as attractants and feeding stimulants for specialist herbivores (Bowers 1991;Marak et al 2002;Biere et al 2004;Beninger et al 2008;Reudler Talsma et al 2008). Moreover, quantitative variation in iridoid glycosides is known to influence plant interactions with generalist and specialist enemies; higher concentrations have been associated with greater negative effects on generalists and positive effects on specialists (e.g., Bowers and Puttick 1989;Biere et al 2004;Harvey et al 2005;Prudic et al 2005;Reudler Talsma et al 2008).…”

A Comparison of Antirrhinoside Distribution in the Organs of Two Related Plantaginaceae Species with Different Reproductive Strategies

“…We have shown that antirrhinoside reduces the growth of another generalist, gypsy moth, at concentrations in artificial diet well below those found in leaves (Beninger et al 2008). Antirrhinoside, therefore, can be classified as a defensive compound, and predictions can be made about its distribution and concentration within plants according to ODT.…”

“…Catalpol was found to be a more potent growth inhibitor of larval Spodoptera eridania (Stoll) than aucubin , and its high concentration in younger leaves is consistent with ODT. The structural similarity and defensive function of catalpol in P. lanceolata as compared to antirrhinoside of Antirrhinum majus L. has been described by Beninger et al (2008).…”

“…Whether they have biological activity at these concentrations is unknown. However, antirrhinoside, can be found in concentrations ranging from 5 to 23% dry weight of plant tissue in A. majus (Beninger et al 2007), and is known to inhibit growth of larval gypsy moth significantly at a concentration of only 3.3% in artificial diet (Beninger et al 2008).…”