Removal of Lichen Secondary Metabolites Affects Food Choice and Survival of Lichenivorous Moth Larvae

Abstract

Host use and selection by herbivores are often determined by host chemistry. Lichen secondary chemicals frequently have been assumed to have a defensive role against herbivores similar to that of higher plants, but thus far there is only circumstantial evidence of the adverse effect of lichen secondary chemicals on specialized lichen‐feeders. We studied the impact of lichen secondary metabolites on performance and host preference of lichenivorous larvae of the moth Eilema depressum using a recently developed manipulation method that allows the removal of a major part of lichen secondary metabolites from the extracellular space of the lichen thallus without harming their primary metabolism. All larvae died on intact thalli of Vulpicida pinastri and Hypogymnia physodes, whereas, after extraction of most of the lichens' secondary chemicals (e.g., pinastric and physodic acids, respectively), survival of neonate larvae ranged between 75% and 85%. In turn, atranorin, the major secondary metabolite in the cortical layer of Parmelia sulcata, merely retarded the growth of larvae during their first days, but had no long‐term impact on survival or performance of larvae. In preference experiments, treated thalli with lowered concentrations of lichen secondary metabolites, with the exception of Xanthoria parietina, were preferred to intact thalli containing secondary chemicals. Our results show that lichen secondary metabolites may act, at natural concentrations, as strong antiherbivore compounds against E. depressum larvae and may play an important role in their host selection.

Host use of a specialist lichen-feeder: dealing with lichen secondary metabolites

“…Half of the larvae were reared on intact control thalli and half on thalli from which secondary chemicals had been removed. On H. physodes we reared only 18 larvae (from Wve females) on both treatments for 14 days, as earlier observations with C. lichenaria and results with E. depressum had shown that larvae were not likely to survive on this lichen species (Pöykkö et al 2005). Lichen thallus was split into two and the slices were randomly assigned either for the treatment or the control.…”

“…These studies have shown that many lichen metabolites hinder the growth and reduce the survival of several generalist herbivores (Slansky 1979;Lawrey 1983Lawrey , 1989Emmerich et al 1993;Giez et al 1994;Gauslaa 2005). It was recently shown by Pöykkö et al (2005) that some lichen secondary metabolites are harmful also to a specialized lichen-feeder, as the removal of most of the secondary chemicals from Vulpicida pinastri and Hypogymnia physodes increased remarkably the survival of neonate larvae of Eilema depressum. In turn, all larvae died on the intact lichen thalli that contained natural amounts of secondary chemicals.…”

“…Lichen secondary metabolites occur in the extracellular space, and may be chemically almost completely removed from a dry lichen thallus without harming the vitality of lichens or their herbivores Gauslaa 1996, 2001;Gauslaa 2005;Pöykkö et al 2005). For example, with acetone treatment over 90% of parietin and ca.…”

“…For example, with acetone treatment over 90% of parietin and ca. 75% of atranorin (including chloroatranorin) can be removed from Xanthoria parietina and Parmelia sulcata thalli, respectively (Pöykkö et al 2005). This allows vigorous testing of the relative importance of lichen secondary metabolites on the performance and host use of lichen-feeding herbivores in vivo.…”

Analysis of Lichen Metabolites, a Variety of Approaches

“…Strong experimental data support protection of lichens from herbivores grazing granted by lichen secondary metabolites (Asplund and Gauslaa 2008;Nimis and Skert 2006;Pöykkö et al 2005;Dailey et al 2008). Ertl (1951) (Nguyen et al 2013).…”