Tree resistance to Lymantria dispar caterpillars: importance and limitations of foliar tannin composition

Abstract

The ability of foliar tannins to increase plant resistance to herbivores is potentially determined by the composition of the tannins; hydrolyzable tannins are much more active as prooxidants in the guts of caterpillars than are condensed tannins. By manipulating the tannin compositions of two contrasting tree species, this work examined: (1) whether increased levels of hydrolyzable tannins increase the resistance of red oak (Quercus rubra L.), a tree with low resistance that produces mainly condensed tannins, and (2) whether increased levels of condensed tannins decrease the resistance of sugar maple (Acer saccharum Marsh.), a tree with relatively high resistance that produces high levels of hydrolyzable tannins. As expected, when Lymantria dispar L. caterpillars ingested oak leaves coated with hydrolyzable tannins, levels of hydrolyzable tannin oxidation increased in their midgut contents. However, increased tannin oxidation had no significant impact on oxidative stress in the surrounding midgut tissues. Although growth efficiencies were decreased by hydrolyzable tannins, growth rates remained unchanged, suggesting that additional hydrolyzable tannins are not sufficient to increase the resistance of oak. In larvae on condensed tannin-coated maple, no antioxidant effects were observed in the midgut, and levels of tannin oxidation remained high. Consequently, neither oxidative stress in midgut tissues nor larval performance were significantly affected by high levels of condensed tannins. Post hoc comparisons of physiological mechanisms related to tree resistance revealed that maple produced not only higher levels of oxidative stress in the midgut lumen and midgut tissues of L. dispar, but also decreased protein utilization efficiency compared with oak. Our results suggest that high levels of hydrolyzable tannins are important for producing oxidative stress, but increased tree resistance to caterpillars may require additional factors, such as those that produce nutritional stress.

Atmospheric change alters foliar quality of host trees and performance of two outbreak insect species

“…For larval growth and consumption, initial larval dry mass was included as a covariate. As a measure of approximate digestibility (AD), we used frass production with consumption as a covariate (Barbehenn et al 2009). Efficiency of conversion of digested food (ECD) was measured as growth, with ''use'' (use = total mass consumed -total frass produced) as a covariate, whereas efficiency of conversion of ingested food (ECI) was measured as growth, with consumption included as a covariate (Knepp et al 2007).…”

Changes in the spatial structure of oak carbon-based secondary compounds after pine harvesting

“…The increase in the tannin-to-N ratio for green leaves in the harvested site would likely alter the nutritional environment for herbivores and pathogens decreasing the efficiency of conversion of digested and ingested matter to body mass (Barbehenn et al, 2009). The increase of this ratio is driven by both an increase in leaf tannins and a decrease in leaf N. This ratio did not show spatial structure in the harvested site due to the loss of the spatial structure of leaf tannins.…”

“…Thus, we hypothesised that the spatial structure of leaf secondary compounds (total phenols, tannins, and non-tannin phenols) in forested stands would disappear in harvested stands for those secondary compounds that strongly depend on light availability. The tannin:N ratio was also considered due to its influence on the efficiency of conversion of digested matter to body mass by herbivories (Barbehenn et al (2009). Complementarily, the spatial structure of leaf secondary compounds would remain unaltered for those compounds that either depend on the availability of other resources or are under major genetic control.…”

Foliage maturity of Quercus ilex affects the larval development of a Croatian coastal population of Lymantria dispar (Lepidoptera: Erebidae)

“…Tannins are accepted as an important resistance factor against herbivory by insects [38]. According to Makkar et al [37] the levels of tannin in holm oak foliage increases as the foliage matures. Furthermore, the results of Bourchier and Nealis [38] study using tannin-supplemented diets were especially pronounced in later instars, where females on a unsupplemented control diet grew at twice the rate of larvae on tannin-supplemented diets.…”