Understanding the factors that influence predator-prey dynamics requires an investigation of oscillations in predator and prey population sizes over time. However, empirical studies are often ...performed over one or fewer predator generations. This is particularly true for studies addressing the non-consumptive effects of predators on prey. In a previous study that lasted less than one predator generation, we demonstrated that two species of parasitoid wasps additively suppressed aphid populations through a combination of consumptive and non-consumptive effects. However, the non-consumptive effects of one wasp reduced the reproductive success of the other, suggesting that a longer-term experiment may have revealed antagonism between the wasps. The goal of our current study is to evaluate multi-generation consumptive and non-consumptive interactions between pea aphids (Acyrthosiphon pisum) and the wasps Aphidius ervi and Aphidius colemani. Aphidius ervi is a common natural enemy of pea aphids. Aphidius colemani is a non-consumptive enemy that does not consume pea aphids, but negatively affects pea aphid performance through behavioral disturbance. Large field cages were installed to monitor aphid abundance in response to the presence and absence of both species of wasp over four weeks (two parasitoid generations). We found that the non-consumptive enemy A. colemani initially controlled the pea aphid population, but control in the absence of parasitism was not sustainable over the long term. Aphidius ervi suppressed pea aphids through a combination of consumptive and non-consumptive effects. This suppression was more effective than that of A. colemani, but aphid abundance fluctuated over time. Suppression by A. ervi and A. colemani together was complementary, leading to the most effective and stable control of pea aphids. Therefore, promoting a diverse natural enemy community that contributes to pest control through consumptive and non-consumptive interactions may enhance the stability of herbivore population suppression over time.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Most studies investigating the importance of non-consumptive interactions for herbivore suppression focus on pairwise interactions between one predator and one prey, ignoring any community context. ...Further, the potential for non-consumptive interactions to arise between herbivores and non-enemy organisms is commonly overlooked. We investigated the relative contributions of consumptive and non-consumptive effects to aphid suppression by a wasp assemblage containing both enemies and non-enemies. We examined the suppression of two aphid species with different defensive strategies, pea aphids (Acyrthosiphon pisum), which drop from their host plant to the ground, and green peach aphids (Myzus persicae), which remain on the plant and merely walk away. The expectation was that riskier defensive behaviors, like abandoning the plant, would result in larger non-consumptive effects. We found that the outcome of multi-species interactions differed depending on the mechanism of suppression, with interference among wasps in their consumptive effects and additivity in their non-consumptive effects. We also found that, despite differences in defensive strategies, the non-consumptive effects of wasps on aphid abundance were significant for both aphid species. Furthermore, when part of a multi-species assemblage, non-enemies enhanced aphid suppression via complementary non-consumptive effects with lethal enemies, but this increase in suppression was offset by disruption in the consumptive suppression of aphids by lethal enemies. We conclude that non-consumptive effects arise from interactions with both enemy and non-enemy species and that both can contribute to herbivore suppression when part of a broader community. We predict that encouraging the presence of non-enemy organisms may provide insurance against fluctuations in the size of consumptive enemy populations and buffer against herbivore outbreaks.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
1. Although crop rotation has been used for centuries to enhance agricultural production, there are surprisingly little data justifying the use of one rotation over another. Growers typically avoid ...growing plants in succession that belong to the same genus or family, but it is not clear whether closely related crops are indeed poor rotation partners and whether evolutionary history, overall, predicts legacy effects in agricultural soils. 2. Here, we use a plant-soil feedback framework to test the relationship between species relatedness and crop growth. Using tomato Solanum lycopersicum as our focal crop, we determined how 36 common crop and weed species that vary along a spectrum of phylogenetic relatedness influence tomato growth in subsequent plantings. We also tested whether soil conditioning affects the performance of an above-ground insect herbivore, the tobacco hornworm Manduca sexta. 3. Phylogenetic relatedness did not predict plant-soil feedback effects on tomato biomass or hornworm performance; rather, impacts of soil conditioning were highly species- or family-specific. For example, tomatoes growing in soil previously containing plants in the Asteraceae family were notably resistant to caterpillar feeding. 4. There was also a disconnect between which plant species caused negative feedbacks on tomatoes vs. hornworms (e.g. thistle Cirsium discolor soil had strong negative effects on herbivory but no impact on plant growth). Hence, negative feedbacks on hornworms are likely due to enhanced defence instead of simply reducing leaf availability. 5. Synthesis and applications. These data demonstrate that, despite being widely recommended by agronomists in most cropping systems, phylogenetic relatedness is a poor predictor for the success of crop pairings in rotation, especially in tomato. Better understanding of species-specific effects of soil conditioning will lend insight into how polycultures can be better designed to optimize crop growth while reducing susceptibility to insect pests, which is particularly useful on diversified farms that cultivate a variety of crop species.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Agriculture has long employed phylogenetic rules whereby farmers are encouraged to rotate taxonomically unrelated plants in shared soil. Although this forms a central tenet of sustainable ...agriculture, strangely, this on‐farm “rule of thumb” has never been rigorously tested in a scientific framework. To experimentally evaluate the relationship between phylogenetic distance and crop performance, we used a plant–soil feedback approach whereby 35 crops and weeds varying in their relatedness to tomato (Solanum lycopersicum) were tested in a two‐year field experiment. We used community profiling of the bacteria and fungi to determine the extent to which soil microbes contribute to phenotypic differences in crop growth. Overall, tomato yield was ca. 15% lower in soil previously cultivated with tomato; yet, past the species level there was no effect of phylogenetic distance on crop performance. Soil microbial communities, on the other hand, were compositionally more similar between close plant relatives. Random forest regression predicted log10 phylogenetic distance to tomato with moderate accuracy (R2 = .52), primarily driven by bacteria in the genus Sphingobium. These data indicate that, beyond avoiding conspecifics, evolutionary history contributes little to understanding plant–soil feedbacks in agricultural fields; however, microbial legacies can be predicted by species identity and relatedness.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Predators are typically evaluated for their potential effectiveness as natural biological control agents by examining traits related to their consumptive relationship with an herbivore. For example, ...voracious predators with a high prey attack rate or predators that specialize in consuming a particular pest species are considered ideal for biological control. However, there is a growing body of research demonstrating that predators also influence herbivore population size through non-consumptive interactions. Non-consumptive interactions include changes in prey behavior, morphology, or lifehistory traits in response to the presence of a predator that allow prey to survive a predator encounter but result in declines in prey fitness due to reduced availability of resources or expending energy that would have been otherwise used for growth or reproduction. The existence of non-consumptive effects is significant because it raises the possibility that a non-lethal organism (i.e. non-enemy) in the environment can also contribute to herbivore suppression if an herbivore inaccurately perceives an organism as a threat and engages in a defensive response. The goal of my dissertation research was to determine whether non-enemies contribute to natural biological control and enhance herbivore suppression beyond levels accomplished by consumptive natural enemies alone. Previous work in our lab demonstrated that pea aphids Acyrthosiphon pisum (Harris) respond to the non-enemy wasp Aphidius colemani Viereck by stopping feeding and dropping off of their host plant, resulting in a decline in pea aphid abundance even though pea aphids are not a host for A. colemani. My work evaluated whether this behavioral suppression of pea aphid populations by the non-enemy wasp is complementary with pea aphid suppression by the consumptive enemy Aphidius ervi Haliday. I investigated 1) the mechanisms responsible for and the magnitude of the non-consumptive effects of A. colemani and A. ervi on pea aphid populations, 2) the contributions of non-consumptive interactions to short-term and long-term suppression of aphid populations in the presence of consumptive natural enemies, and 3) the feasibility of increasing plant diversity in the field to enhance pea aphid suppression by facilitating behavioral non-consumptive interactions. I found that pea aphids respond to interactions with both wasp species, but they more frequently engaged in defensive behaviors such as dropping in the presence of the enemy A. ervi than the non-enemy A. colemani. The behavioral response of the pea aphid to the presence of the non-enemy was strong enough for A. colemani to suppress pea aphid populations in the short term, but this suppression was not maintained over the long term. When the non-enemy A. colemani was combined with the consumptive enemy A. ervi, there was some evidence for antagonism between the wasps over the short term. However, the non-enemy and enemy were complementary in their suppression of pea aphid populations over the long term, with more consistent and stable suppression when both wasps were present. I also demonstrated that increasing plant diversity in a field setting enhances suppression of pea aphid populations by promoting interactions between pea aphids and non-enemies. My work demonstrates that non-lethal organisms, or non-enemies, in the environment have an important role to play in influencing herbivore abundance, and that the addition of non-enemies to a community of lethal predators and parasitoids can lead to greater and more consistent suppression of herbivores in the long term.
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