Plant water stress and previous herbivore damage affect insect performance

Abstract

Abstract. 1. Short-term changes in plant resistance traits can be affected by abiotic factors or damage by herbivores, although how the combined effects of abiotic factors and previous damage affect subsequent insect larval development is not well understood.2. Complementary glasshouse and field experiments were conducted to evaluate whether plant water stress and previous herbivore damage influenced monarch (Danaus plexippus) larval development on common milkweed, Asclepias syriaca.3. In the glasshouse, water stress altered a suite of A. syriaca functional traits but did not affect nutrient content, whereas herbivore damage increased leaf nitrogen (N) and reduced the carbon:nitrogen (C:N) ratio. A bioassay experiment showed that monarch larval survival was lower on well-watered plants that were previously damaged by monarch larva than on damaged and drought-stressed plants. Bioassay larvae consumed less leaf tissue of previously damaged plants, whereas monarch larval mass was affected additively by water stress and previous damage, after correcting for the amount of leaf tissue consumed.4. In a 2-year field experiment, monarch larval performance was higher on previously damaged A. syriaca plants that received experimentally reduced rainfall, relative to plants receiving ambient rainfall.5. Collectively, these results from glasshouse and field experiments suggest that insect performance was highest on previously damaged plants under water stress and highlight the additive and interactive roles of abiotic and biotic factors on herbivore performance.

Population Variation, Environmental Gradients, and the Evolutionary Ecology of Plant Defense against Herbivory

“…As a result, most existing studies do not inform understanding of how growth and defense covary among populations that occur across resource gradients. The few that have examined among-population patterns often do not find growth-defense trade-offs (Hahn and Maron 2016). We hypothesize that more favorable resource environments should facilitate greater levels of growth, support greater herbivore numbers, and therefore favor greater plant defense as well.…”

“…On the basis of its intuitive appeal and widespread empirical support (Endara and Coley 2011;Massad et al 2011), the RAH has also been invoked to explain intraspecific patterns in plant defense allocation. Although some studies support the RAH (e.g., Woods et al 2012;Burghardt 2016;Stevens et al 2016), there is generally poor support for it within species (Hahn and Maron 2016). The RAH has also been extended to describe intraspecific variation in growth and defense at both the physiological level and the evolutionary level (Herms and Mattson 1992).…”

“…However, resource availability may increase overall plant "vigor" (i.e., plants have more resources to allocate to multiple traits), which could mask trade-offs among other traits (Agrawal 2011). In summary, while trade-offs may be expected among species, neutral or positive growth-defense relationships may be more likely among populations due to adaptation to differential herbivory and resource availability (Hahn and Maron 2016).…”

“…We hypothesize that more favorable resource environments should facilitate greater levels of growth, support greater herbivore numbers, and therefore favor greater plant defense as well. Thus, we have predicted that within species, there should be positive growth-defense relationships among populations that occur across resource gradients (Hahn and Maron 2016).…”

Relative importance of drought, soil quality, and plant species in determining the strength of plant–herbivore interactions

“…While this situation is quite likely for the variation in the nutrient content in natural conditions (e.g. Hale et al, 2003;Staley et al, 2006Staley et al, , 2007Hahn & Maron, 2018;Nguyen et al, 2018;Rai et al, 2018), investigating these effects was not the topic of our study. More likely, all the plants within a single area will experience severe drought, especially in the course of the current climate change (IPCC, 2014).…”