The Use and Usefulness of Artificial Herbivory in Plant-Herbivore Studies

Abstract

Artificial damage is a popular method in plant-herbivore studies, because the use of real herbivores is often laborious and because it may be virtually impossible to use herbivores in many experimental setups. We made a literature search of studies that tested whether natural and artificial damage have similar effects on plants. Of 46 studies found, 33 (72 %) reported a significant difference between responses to artificial and natural herbivore damage in at least one of the statistical tests included. The studies contained 280 statistical tests, of which 99 (35 %) showed a significant difference between artificial and natural damage. Phytochemical responses to artificial and natural damage were different in 41 % of the statistical tests and 75 % of the studies found at least one significant difference. Plant resistance, measured as secondary damage, herbivore performance, fungal growth in damaged tissue or plant attractivity to parasitoids of herbivores, differed in 60 % of the statistical tests and 85 % of the studies had significant differences. Growth, reproduction and physiological responses to artificial and natural damage differed in 20-30 % of statistical tests and 50-83 % of studies had significant differences. Thus, studies on plant tolerance (growth and reproduction after damage) more often showed similar effects for artificial and natural damage than studies on plant resistance to herbivory, but even in tolerance studies artificial and natural damage often have different effects. Some studies indicated that application of herbivore saliva and careful imitation of timing and spatial pattern of damage helped in reaching the same effect with simulations and natural damage. IntroductionIn many experimental settings, artificial damage has several practical benefits over the use of real herbivores (Hjältén, Chap. 12, this Vol.). The extent of damage and the location of damaged parts can easily be controlled, and collateral damage to other than target tissues can be minimized. The removed biomass can be collected and measured. Furthermore, there is no need to collect and rear herbivores. The use of artificial damage enables efficient experimental designs, with balanced sample sizes of experimental groups and a low variation of treatment intensity within each experimental group. For these reasons, artificial damage is used more often in herbivory research than real herbivores.Artificial damage does not, however, always adequately mimic natural damage (Baldwin 1990; Hjältén, Chap. 12, this Vol.). Many types of herbivory are not applicable for simulations. Damage by stem borers, miners, galling insects, root feeders or sucking insects is seldom tried to simulate. However, even when the apparent damage pattern is easy to reproduce, several characteristics of natural herbivory may be difficult to simulate, such as the timing of damage, herbivore host choice, location of damage within a plant, and subtle details of damage by herbivore mouth parts. Herbivore saliva can also play a role in plant responses (Walling ...

The association among herbivory tolerance, ploidy level, and herbivory pressure in cardamine pratensis

“…Because we standardized the total damage, we assume that variation in the amount of insect damage among plants had a negligible contribution to variation in tolerance. According to a review, the effects of natural and artificial damage on tolerance are fairly similar (Lehtilä and Boalt 2004). To mimic natural growth environment, the potted plants were transferred to a semi-forested enclosure after herbivore damage treatment.…”

Arbuscular mycorrhizal colonization in black poplar roots after defoliation by a non-native and a native insect

“…No defoliation theses showed any significant differences compared to the undefoliated ones. Despite several studies simulated herbivory effects on plants using mechanical defoliation or included mechanically defoliated control plants, this approach is deemed appropriate when studying simple biotic interactions, but not necessarily for complex interactions including different trophic levels (Hjältén 2004, Lehtilä & Boalt 2004, as the ones investigated. Although most of the papers published on AM symbiosis report open field experiments, pot experiments in semi-controlled conditions, like those performed in this work, have allowed to study some of the mechanisms involved in plant-AM fungi interaction under defoliation conditions.…”

Induced twining in Ipomoea purpurea (L.) Roth.: response threshold and induction by volatiles and snail damage

“…In natural conditions, I. purpurea individuals can be exposed to snail damage (personal observation) or volatile emissions from neighbor plants and the induced twining could help reduce further damage to apical portions of the plant (Gianoli & Molina-Montenegro 2005, Atala & Gianoli 2008. It has been suggested that natural damage is qualitatively and quantitatively different from artifi cial damage , Lehtilä & Boalt 2004. Results show that artifi cial and natural damage can induce twining in I. purpurea, giving the response an ecological relevance that could impact natural populations, reducing further leaf damage and, therefore, increasing fi tness in the presence of herbivores.…”

“…Artifi cial damage to the leaves and chemical induction under controlled conditions are useful tools for assessing induced responses. However, the application of natural damage (e.g., exposition to herbivores) could be more relevant to understanding the twining in an ecological context , Lehtilä & Boalt 2004.…”