Text by Lauri Laanisto
Another paper by Ülo´s former postdoc Lucian, who does a lot of small experiments, where they measure all sorts of factors that could affect organic volatile emissions in plants. This time the focus is on the interplay between an oak and a moth. The topic is actually pretty interesting, or more precisely – it is something that we need to study. Climate change and the loss of ecosystem services like pest control (whether due to climate change or not) will change the invertebrate herbivore dynamics on plants in forseeable future. How significantly will it change the things, especially on small scale. So far we have very little idea about that. And this study tries to take the first steps in this direction.
As a remark I have to say that studying gypsy moth feels very-very Romanian thing to do;) I´m sure that soon the common name will be changed (like blackboys in Australia are now known as grasstrees etc). Maybe the Romani representatives have not yet had time to deal with such racial taxonomy…
Citation: Copolovici, L., Pag, A., Kännaste, A., Bodescu, A., Tomescu, D., Copolovici, D., … & Niinemets, Ü. (2017). Disproportionate photosynthetic decline and inverse relationship between constitutive and induced volatile emissions upon feeding of Quercus robur leaves by large larvae of gypsy moth (Lymantria dispar). Environmental and Experimental Botany, 138: 184–192. (link to full text)
Progressive spread of the gypsy moth (L. dispar) across north east US from 1900–2007; compiled from county data by US Forest Service (pic from here)
Gypsy moth (Lymantria dispar L., Lymantriinae) is a major pest of pedunculate oak (Quercus robur) forests in Europe, but how its infections scale with foliage physiological characteristics, in particular with photosynthesis rates and emissions of volatile organic compounds has not been studied. Differently from the majority of insect herbivores, large larvae of L. dispar rapidly consume leaf area, and can also bite through tough tissues, including secondary and primary leaf veins. Given the rapid and devastating feeding responses, we hypothesized that infection of Q. robur leaves by L. dispar leads to disproportionate scaling of leaf photosynthesis and constitutive isoprene emissions with damaged leaf area, and to less prominent enhancements of induced volatile release. Leaves with 0% (control) to 50% of leaf area removed by larvae were studied. Across this range of infection severity, all physiological characteristics were quantitatively correlated with the degree of damage, but all these traits changed disproportionately with the degree of damage. The net assimilation rate was reduced by almost 10-fold and constitutive isoprene emissions by more than 7-fold, whereas the emissions of green leaf volatiles, monoterpenes, methyl salicylate and the homoterpene (3E)-4,8-dimethy-1,3,7-nonatriene scaled negatively and almost linearly with net assimilation rate through damage treatments. This study demonstrates that feeding by large insect herbivores disproportionately alters photosynthetic rate and constitutive isoprene emissions. Furthermore, the leaves have a surprisingly large capacity for enhancement of induced emissions even when foliage photosynthetic function is severely impaired.