Plant resistance reduces the strength of consumptive and non‐consumptive effects of predators on aphids

Abstract

Summary1. The impact of predators on prey has traditionally been attributed to the act of consumption. Prey responses to the presence of the predator (non-consumptive effects), however, can be as important as predation itself. While plant defences are known to influence predatorprey interactions, their relative effects on consumptive vs. non-consumptive effects are not well understood. 2. We evaluated the consequences of plant resistance and predators (Hippodamia convergens) on the mass, number of nymphs, population growth, density and dispersal of aphids (Macrosiphum euphorbiae). We tested for the effects of plant resistance on non-consumptive and consumptive effects of predators on aphid performance and dispersal using a combination of path analysis and experimental manipulation of predation risk. 3. We manipulated plant resistance using genetically modified lines of tomato (Solanum lycopersicum) that vary incrementally in the expression of the jasmonate pathway, which mediates induced resistance to insects and manipulated aphid exposure to lethal and risk predators. Predation risk predators had mandibles impaired to prevent killing. 4. Plant resistance reduced predation rate (consumptive effect) on high resistance plants. As a consequence, predators had no impact on the number of nymphs, aphid density or population growth on high resistance plants, whereas on low resistance plants, predators reduced aphid density by 35% and population growth by 86%. Path analysis and direct manipulation of predation risk showed that predation risk rather than predation rate promoted aphid dispersal and varied with host plant resistance. Aphid dispersal in response to predation risk was greater on low compared to high resistance plants. The predation risk experiment also showed that the number of aphid nymphs increased in the presence of risk predators but did not translate into increased population growth. 5. In conclusion, the consumptive and non-consumptive components of predators affect different aspects of prey demography, acting together to shape prey population dynamics. While predation risk accounts for most of the total effect of the predator on aphid dispersal and number of nymphs, the suppressive effect of predators on aphid population occurred largely through consumption. These effects are strongly influenced by plant resistance levels, suggesting that they are context dependent.

Constitutive and herbivore‐induced plant defences regulate herbivore population processes

“…Aphids feeding on these plants are larger in size (Kersch-Becker & Thaler, 2015) and when densities rise aphid per capita honeydew excretion is reduced, suggesting that at high densities aphids are consuming less food. Aphids feeding on these plants are larger in size (Kersch-Becker & Thaler, 2015) and when densities rise aphid per capita honeydew excretion is reduced, suggesting that at high densities aphids are consuming less food.…”

“…We took an experimental approach by conducting herbivore density manipulations, using a model plant in which resistance has been genetically altered to elevate or suppress jasmonate plant defences. Prosystemin;McGurl, Orozco-Cardenas, Pearce, & Ryan, 1994), and therefore has constitutively high levels of JA-dependent defences conferring high resistance to aphids (Kersch-Becker et al, 2017;Kersch-Becker & Thaler, 2015). We used three genetically modified tomato lines that vary in the expression of JA pathway: (a) jasmonate-insensitive-a mutant tomato line (cv.…”

Consumptive and nonconsumptive effect ratios depend on interaction between plant quality and hunting behavior of omnivorous predators

“…Recently, Kersch‐Becker and Thaler (2015) investigated the interaction between consumptive, nonconsumptive effects and host plant resistance, using genetically modified plants and predators with impaired mandibles. Herbivore‐induced plant volatiles may have changed the predator's (lady beetle) foraging behavior.…”

Tri‐trophic interactions mediate the spread of a vector‐borne plant pathogen

“…). For example, when plants express resistance to vectors, vector abundance decreases, which can in turn limit the ability of predators to find and consume vector prey (Kersch‐Becker and Thaler ). This suggests that a better assessment of how tri‐trophic interactions involving vectors affect pathogens in complex food webs could greatly increase our understanding of disease ecology.…”