The Experts below are selected from a list of 225 Experts worldwide ranked by ideXlab platform
Peter B. Mcevoy - One of the best experts on this subject based on the ideXlab platform.
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Evolving while invading: rapid adaptive evolution in juvenile development time for a biological control organism colonizing a high-elevation environment.
Evolutionary applications, 2012Co-Authors: Peter B. Mcevoy, Kimberley M. Higgs, E. M. Coombs, Evrim Karaçetin, Leigh Ann Harrod StarcevichAbstract:We report evidence of adaptive evolution in juvenile development time on a decadal timescale for the cinnabar moth Tyria jacobaeae (Lepidoptera: Arctiidae) colonizing new habitats and hosts from the Willamette Valley to the Coast Range and Cascades Mountains in Oregon. Four lines of evidence reveal shorter egg to pupa juvenile development times evolved in the mountains, where cooler temperatures shorten the growing season: (i) field observations showed that the mountain populations have shorter phenological development; (ii) a common garden experiment revealed genetic determination of phenotypic differences in juvenile development time between Willamette Valley and mountain populations correlated with the growing season; (iii) a laboratory experiment rearing offspring from parental crosses within and between Willamette Valley and Cascades populations demonstrated polygenic inheritance, high heritability, and genetic determination of phenotypic differences in development times; and (iv) statistical tests that exclude random processes (founder effect, genetic drift) in favor of natural selection as explanations for observed differences in phenology. These results support the hypothesis that rapid adaptation to the cooler mountain climate occurred in populations established from populations in the warmer valley climate. Our findings should motivate regulators to require evaluation of evolutionary potential of candidate biological control organisms prior to release.
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Controlling a plant invader by targeted disruption of its life cycle
Journal of Applied Ecology, 2012Co-Authors: Joseph T. Dauer, Peter B. Mcevoy, John Van SickleAbstract:Summary 1. Pest management strategies should be informed by research on a broad suite of biotic and abiotic interactions. We used a life table response experiment (LTRE) to assess the reliability of ragwort Jacobaea vulgaris management recommendations based on interactions of (i) time of disturbance to initiate experimental units, (ii) herbivory from two biological control organisms, the cinnabar moth Tyria jacobaeae and ragwort flea beetle Longitarsus jacobaeae and (iii) interspecific competition by perennial grasses. 2. Our LTRE combines a factorial experiment with a linear, deterministic matrix model for ragwort populations representing transitions among three stages: 1st year juveniles, ≥2nd year juveniles and adults. Elasticity analysis identified potentially vulnerable ragwort transitions, and a contributions analysis confirmed which treatments influenced these transitions. Ultimate treatment effects were quantified as the reduction in population growth rates and time to local extinction. 3. Elasticity analyses found the ragwort’s biennial pathway, juvenile to adult transition and fertility transition were most influential and most amenable to manipulation across all community configurations. The flea beetle and perennial grass competition had negative effects on survival and fertility, whereas the cinnabar moth only reduced fertility and induced the perennial pathway. 4. All combinations of insects or increased plant competition reduced the growth rate of ragwort. Full interspecific competition and the flea beetle resulted in a significantly greater and faster decline in the ragwort populations than the cinnabar moth. Moreover, this pattern was consistent between two times of initial disturbance. 5.Synthesis and applications. Maximizing plant competition provides the fastest way to control ragwort. If this option is unavailable, for example, grazed or disturbed land, the ragwort flea beetle provides excellent management to lower ragwort densities without the potential nontarget effects of the cinnabar moth. Factorial experiments and matrix models help to evaluate interacting factors that influence invasive species’ vulnerabilities, inform how to intervene in a weed life cycle to reduce weed abundance and confirm recommendations that are robust to community variation.
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Local Dispersal by the Cinnabar Moth Tyria jacobaeae
Ecological Applications, 1996Co-Authors: Nathan T. Rudd, Peter B. McevoyAbstract:We used mark-recapture data to measure and model movement by the adult stage of the cinnabar moth Tyria jacobaeae (Lepidoptera, Arctiidae). Our objectives were: (1) to standardize the description of cinnabar moth movement and thereby provide a more reliable basis for comparison and extrapolation, and (2) to screen the potential influence of gender, physical condition, time, spatial location, and spatial heterogeneity in the environment on movement parameters. Recapture rates depended on wing wear (low 16%, high 11%) but were independent of behavior immediately after release (mobile 15%, immobile 14%), gender (male 13%, female 16%), or location in the study area (central 15%, peripheral 15%). Thus, mortality and/or emigration was greater for individuals with high wing wear compared to those with low wing wear. Moths were aggregated at the southwest margin of the study area both at initial capture and recapture. The direction of movement was biased in north and south directions, perhaps because forests on the east and west boundaries created a corridor channeling movement. The movement observed within a single generation did not conform to simple diffusion, which predicts that the mean square displacement (MSD) increases linearly with time. Instead, observed movement rates varied over time, and the relationship between MSD and time varied by gender, smoothly decelerating in males and erratically increasing in females. Observed movement (represented by the frequency distribution of displacements x for each time t with time measured at a daily resolution) was adequately approximated by a Weibull distribution, for which estimates of the shape and scale parameters were calculated. Male distributions were more frequently mounded, associated with higher values of the shape parameter α, and the scale of male distributions shifted sooner to longer distances, associated with higher values of the scale parameter β. The Weibull parameters varied by sex and time, suggesting that males were initially more mobile than females, but the magnitude of the difference varied over time. The speed and direction of individual movement were independent of the moth's spatial location within the field. We conclude that (1) movement speed depended on gender and time, while movement direction was related to spatial heterogeneity in the environment, and (2) much of the disagreement about movement rates among studies of the cinnabar moth can be related to researchers taking measurements and drawing inferences on different scales of observation, and therefore arriving at conflicting results.
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effects of vegetation disturbances on insect biological control of tansy ragwort senecio jacobaea
Ecological Applications, 1993Co-Authors: Peter B. Mcevoy, Nathan T. RuddAbstract:Our study had two major objectives: (1) to clarify the roles of buried seed and different types of localized disturbance in activating outbreaks of a pasture weed (tansy ragwort, Senecio jacobaea), and (2) to measure the effectiveness of two natural enemies (the cinnabar moth Tyria jacobaeae and a ragwort flea beetle, Longitarsus jacobaeae) in inhibiting weed population increase and spread. We conducted a 5-yr field experiment on the coast of Oregon using a randomized-block design with four blocks x three levels of disturbance (background vegetation was Tilled, Clipped, Unaltered) x two levels of cin- nabar moth (Exposed, Protected) x two levels of flea beetle (Exposed, Protected) = 48 plots (each plot was 0.25 m2). Disturbance consistently increased ragwort abundance (measured as density of juve- niles, adults, and their offspring; cover; and biomass); the effect was generally greater in Tilled compared to Clipped disturbance treatments. We also found striking differences in the contribution of each natural enemy to ragwort control. The flea beetle quickly reduced ragwort survival, and this led to a strong and rapid reduction in ragwort abundance. The cinnabar moth reduced ragwort fecundity, but this did not translate into reductions in ragwort cover (measured in 1986 and 1987) or biomass (measured annually from 1986 through 1990). These results establish that (1) ragwort populations were limited more by availability of microsites for germination and establishment than by availability of seed, (2) the ragwort flea beetle was the key factor regulating ragwort abundance, and (3) reduction in ragwort fecundity by the cinnabar moth had little effect on the dynamics of ragwort populations on local scales of space and time. These findings underscore the value of field experiments for investigating the dynamics of biological control systems, the manner in which they are regulated, and their response to perturbation. They further establish how colonization and invasion by ragwort depend on attributes of the disturbance and of natural enemy regimes.
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disturbance competition and herbivory effects on ragwort senecio jacobaea populations
Ecological Monographs, 1993Co-Authors: Peter B. Mcevoy, Caroline Cox, Nathan T. Rudd, Manuela HusoAbstract:The balance of forces determining the successful control of ragwort Senecio jacobaea by introduced insects was investigated in a field experiment by manipulating the time of disturbance, the level of interspecific plant competition, and the level of herbivory by the cinnabar moth Tyria jacobaeae and the ragwort flea beetle Longitarsus jacobaeae. We used a factorial design containing 0.25—m2 plots arranged as 4 Blocks × 2 Disturbance Time (plots were tilled in Fall 1986 or Spring 1987) × 3 Plant Competition levels (vegetation other than ragwort was Removed, Clipped, or Unaltered) × 2 Cinnabar Moth levels (Exposed, Protected) × 2 Flea Beetle levels (Exposed, protected). The response of ragwort was measured as colonization, survivorship, and reproduction of the first ragwort generation, establishment of juveniles in the second generation, and changes in ragwort biomass from 1987 through 1990. We also made annual measurements from 1987 through 1990 of the allocation of space (the limiting resource in the Unaltered competition treatment) among the categories ragwort, other species, litter, and open space. Natural enemy responses were characterized by relating variation in the concentration of enemies and the concentration of ragwort among patches. We found that abundant buried seed and localized disturbances combined to activate incipient ragwort outbreaks, and that interspecific plant competition and herbivory by the ragwort flea beetle combined to inhibit the increase and spread of incipient outbreaks. Time of disturbance had little effect on the outcome of biological control. Under conditions in the Removed and Clipped treatments (where there was sufficient open space for germination and establishment), reduction in seed production in the first generation caused by cinnabar moth larvae led to a reduction in plant numbers in the second generation, but caused only a weak effect on ragwort cover and no detectable effect on ragwort biomass over the longer term from 1986 through 1990. At the spatial scale examined, inhibition by the ragwort flea beetle and plant competition took the extreme form of elimination of all ragwort individuals except the pool of seed buried in the soil. Our findings lead us to (1) reject the view that successful biological control leads to a stable pest—enemy equilibrium on a local spatial scale, (2) strongly endorse "search and destroy" and weakly endorse "complementary enemies" strategies suggested by Murdoch et al. (1985) as ways to improve control, and (3) emphasize resource limitation in the pest at low density as a key feature distinguishing biological control of weeds from biological control of insects.
Klaas Vrieling - One of the best experts on this subject based on the ideXlab platform.
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Local adaptation in oviposition choice of a specialist herbivore: The cinnabar moth
Acta Oecologica, 2017Co-Authors: Xianqin Wei, Patrick P.j. Mulder, Klaas Vrieling, Peter G. L. KlinkhamerAbstract:Abstract Specialist herbivores feed on a restricted number of related plant species and may suffer food shortage if overexploitation leads to periodic defoliation of their food plants. The density, size and quality of food plants are important factors that determine the host plant choice of specialist herbivores. To explore how all these factors influence their oviposition behaviour, we used the cinnabar moth Tyria jacobaeae and the hybrids of a cross between Jacobaea vulgaris and J. aquatica as a study system. While defoliation by the cinnabar moth is common in the coastal area of The Netherlands, it is relatively rare in inland ragwort population. Ragworts contain pyrrolizidine alkaloids (PAs) and those that are found in coastal areas are rich in jacobine-like PAs while those that occur inland are rich in erucifoline-like PAs. We tested how the oviposition preference was influenced by plant size, nitrogen and water content and PA composition. We used cinnabar moth populations from a regularly defoliated area, Meijendel, and Bertogne, a rarely defoliated area. Our results revealed no effects of nitrogen or water content on oviposition preference. Moths from both populations laid larger egg batches on the plants rich in jacobine-like PAs. Moths from Meijendel preferred larger plants and spread their eggs over more egg batches that were, on average, smaller than those of Bertogne moths. These results suggest that Meijendel moths adopted a oviposition strategy to cope with potential defoliation.
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Parallel evolution in an invasive plant: effect of herbivores on competitive ability and regrowth of Jacobaea vulgaris.
Ecology letters, 2015Co-Authors: Tiantian Lin, Peter G. L. Klinkhamer, Klaas VrielingAbstract:A shift in the composition of the herbivore guild in the invasive range is expected to select for plants with a higher competitive ability, a lower regrowth capacity and a lower investment in defence. We show here that parallel evolution took place in three geographically distinct invasive regions that differed significantly in climatic conditions. This makes it most likely that indeed the shifts in herbivore guilds were causal to the evolutionary changes. We studied competitive ability and regrowth of invasive and native Jacobaea vulgaris using an intraspecific competition set-up with and without herbivory. Without herbivores invasive genotypes have a higher competitive ability than native genotypes. The invasive genotypes were less preferred by the generalist Mamestra brassicae but more preferred by the specialist Tyria jacobaeae, consequently their competitive ability was significantly increased by the first and reduced by the latter. Invasive genotypes showed a lower regrowth ability in both herbivore treatments.
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Pyrrolizidine alkaloid composition influences cinnabar moth oviposition preferences in Jacobaea hybrids.
Journal of Chemical Ecology, 2013Co-Authors: Dandan Cheng, Ed Van Der Meijden, Klaas Vrieling, Patrick P.j. Mulder, Peter G. L. KlinkhamerAbstract:Plants produce a variety of secondary metabolites (PSMs) that may be selective against herbivores. Yet, specialist herbivores may use PSMs as cues for host recognition, oviposition, and feeding stimulation, or for their own defense against parasites and predators. This summarizes a dual role of PSMs: deter generalists but attract specialists. It is not clear yet whether specialist herbivores are a selective force in the evolution of PSM diversity. A prerequisite for such a selective force would be that the preference and/or performance of specialists is influenced by PSMs. To investigate these questions, we conducted an oviposition experiment with cinnabar moths (Tyria jacobaeae) and plants from an artificial hybrid family of Jacobaea vulgaris and Jacobaea aquatica. The cinnabar moth is a specialist herbivore of J. vulgaris and is adapted to pyrrolizidine alkaloids (PAs), defensive PSMs of these plants. The number of eggs and egg batches oviposited by the moths were dependent on plant genotype and positively correlated to concentrations of tertiary amines of jacobine-like PAs and some otosenine-like PAs. The other PAs did not correlate with oviposition preference. Results suggest that host plant PAs influence cinnabar moth oviposition preference, and that this insect is a potential selective factor against a high concentration of some individual PAs, especially those that are also involved in resistance against generalist herbivores.
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Chemical ecology of the cinnabar moth (Tyria jacobaeae) on a newly recorded host Senecio adonidifolius
Acta Oecologica, 2006Co-Authors: Klaas VrielingAbstract:Abstract The cinnabar moth ( Tyria jacobaeae , Arctiidae) normally feeds on Senecio jacobaea in the field. For the first time, naturally occurring populations of T. jacobaeae have been found thriving on Senecio adonidifolius , even though the moth's preferred host, S. jacobaea , is available within 50–400 m. In the laboratory, the cinnabar moth has been shown to feed on and develop on S. adonidifolius despite its different leaf morphology, pyrrolizidine alkaloid (PA) profile and a large taxonomic distance to S. jacobaea . Here I examined whether T. jacobaeae has adapted to this new host in the field using adult oviposition behavior and plant acquired defense chemistry in pupae as criteria. Choice tests indicated local adaptation to this newly recorded host. T. jacobaeae reared on S. adonidifolius hosts laid more egg batches and total eggs on it than T. jacobaeae from S. jacobaea . The egg batches were smaller on S. adonidifolius possibly due to highly pinnate thread-like structure of its leaves. The bouquet of plant acquired PAs and the insect metabolized callimorphine in pupae differed widely between pupae collected from the two hosts. T. jacobaeae pupae taken from S. adonidifolius hosts contained more of the insect metabolized callimorphine than pupae taken from S. jacobaea hosts, but they did not differ in total PA concentration. Pupae taken from S. jacobaea hosts contained more unmetabolized plant PA's than pupae from S. adonidifolius hosts. Additionally, 10% of T. jacobaeae larvae taken from S. adonidifolius in Biausse were infested with Carcelia dubia , a parasitic and rare tachinid fly that typically attacks arctiid moths.
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pyrrolizidine alkaloids as oviposition stimulants for the cinnabar moth Tyria jacobaeae
Journal of Chemical Ecology, 2003Co-Authors: Mirka Macel, Klaas VrielingAbstract:In choice experiments with artificial leaves, we tested related pyrrolizidine alkaloids (PAs) for their stimulatory effects on the oviposition of the cinnabar moth, a specialist on the PA-containing plant Senecio jacobaea. The PAs from S. jacobaea that we tested stimulated oviposition. Monocrotaline also stimulated oviposition although this PA is not found in plants of the genus Senecio. The moths preferred ovipositing on filter paper with a PA mixture extracted from S. jacobaea to ovipositing on filter paper with single PAs. Senkirkine, heliotrine, and retrorsine did not stimulate oviposition. The nonactive retrorsine differs only in one OH group to the active senecionine, indicating that small structural differences alter the stimulatory activity of PAs. However, a PA mixture extracted from a nonhost plant, Senecio inaequidens, that consisted of 81% of the nonactive retrorsine did stimulate oviposition. Oviposition preferences between Senecio species seem to be determined by chemical compounds other than PAs.
Peter G. L. Klinkhamer - One of the best experts on this subject based on the ideXlab platform.
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Local adaptation in oviposition choice of a specialist herbivore: The cinnabar moth
Acta Oecologica, 2017Co-Authors: Xianqin Wei, Patrick P.j. Mulder, Klaas Vrieling, Peter G. L. KlinkhamerAbstract:Abstract Specialist herbivores feed on a restricted number of related plant species and may suffer food shortage if overexploitation leads to periodic defoliation of their food plants. The density, size and quality of food plants are important factors that determine the host plant choice of specialist herbivores. To explore how all these factors influence their oviposition behaviour, we used the cinnabar moth Tyria jacobaeae and the hybrids of a cross between Jacobaea vulgaris and J. aquatica as a study system. While defoliation by the cinnabar moth is common in the coastal area of The Netherlands, it is relatively rare in inland ragwort population. Ragworts contain pyrrolizidine alkaloids (PAs) and those that are found in coastal areas are rich in jacobine-like PAs while those that occur inland are rich in erucifoline-like PAs. We tested how the oviposition preference was influenced by plant size, nitrogen and water content and PA composition. We used cinnabar moth populations from a regularly defoliated area, Meijendel, and Bertogne, a rarely defoliated area. Our results revealed no effects of nitrogen or water content on oviposition preference. Moths from both populations laid larger egg batches on the plants rich in jacobine-like PAs. Moths from Meijendel preferred larger plants and spread their eggs over more egg batches that were, on average, smaller than those of Bertogne moths. These results suggest that Meijendel moths adopted a oviposition strategy to cope with potential defoliation.
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Parallel evolution in an invasive plant: effect of herbivores on competitive ability and regrowth of Jacobaea vulgaris.
Ecology letters, 2015Co-Authors: Tiantian Lin, Peter G. L. Klinkhamer, Klaas VrielingAbstract:A shift in the composition of the herbivore guild in the invasive range is expected to select for plants with a higher competitive ability, a lower regrowth capacity and a lower investment in defence. We show here that parallel evolution took place in three geographically distinct invasive regions that differed significantly in climatic conditions. This makes it most likely that indeed the shifts in herbivore guilds were causal to the evolutionary changes. We studied competitive ability and regrowth of invasive and native Jacobaea vulgaris using an intraspecific competition set-up with and without herbivory. Without herbivores invasive genotypes have a higher competitive ability than native genotypes. The invasive genotypes were less preferred by the generalist Mamestra brassicae but more preferred by the specialist Tyria jacobaeae, consequently their competitive ability was significantly increased by the first and reduced by the latter. Invasive genotypes showed a lower regrowth ability in both herbivore treatments.
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Pyrrolizidine alkaloid composition influences cinnabar moth oviposition preferences in Jacobaea hybrids.
Journal of Chemical Ecology, 2013Co-Authors: Dandan Cheng, Ed Van Der Meijden, Klaas Vrieling, Patrick P.j. Mulder, Peter G. L. KlinkhamerAbstract:Plants produce a variety of secondary metabolites (PSMs) that may be selective against herbivores. Yet, specialist herbivores may use PSMs as cues for host recognition, oviposition, and feeding stimulation, or for their own defense against parasites and predators. This summarizes a dual role of PSMs: deter generalists but attract specialists. It is not clear yet whether specialist herbivores are a selective force in the evolution of PSM diversity. A prerequisite for such a selective force would be that the preference and/or performance of specialists is influenced by PSMs. To investigate these questions, we conducted an oviposition experiment with cinnabar moths (Tyria jacobaeae) and plants from an artificial hybrid family of Jacobaea vulgaris and Jacobaea aquatica. The cinnabar moth is a specialist herbivore of J. vulgaris and is adapted to pyrrolizidine alkaloids (PAs), defensive PSMs of these plants. The number of eggs and egg batches oviposited by the moths were dependent on plant genotype and positively correlated to concentrations of tertiary amines of jacobine-like PAs and some otosenine-like PAs. The other PAs did not correlate with oviposition preference. Results suggest that host plant PAs influence cinnabar moth oviposition preference, and that this insect is a potential selective factor against a high concentration of some individual PAs, especially those that are also involved in resistance against generalist herbivores.
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chemotype of senecio jacobaea affects damage by pathogens and insect herbivores in the field
Evolutionary Ecology, 2010Co-Authors: Mirka Macel, Peter G. L. KlinkhamerAbstract:The evolution of the diversity of plant secondary metabolites is still poorly understood. To determine whether natural enemies could exert selection on plant secondary chemistry, pathogen infestation and invertebrate herbivory were measured on 10 genotypes of Senecio jacobaea (Tansy Ragwort) at two experimental field sites during a 2-year period. The genotypes represented two chemotypes based on the presence of the pyrrolizidine alkaloids (PA) jacobine and erucifoline. At one site, Heteren, mainly generalist herbivores were present. Here, damage was limited and did not differ among genotypes or chemotypes. At the other site, Meijendel, several specialists attacked the plants. Damage increased during the year, with a peak in July when most damage was caused by the specialist moth Tyria jacobaeae. At this peak there was no difference in damage among chemotypes. In the months prior to T. jacobaeae damage, chemotypes with jacobine were more severely attacked by specialists than the chemotypes without jacobine. Total damage during that period was positively correlated with both total PA concentration and jacobine concentration. Probably plant vigor also played a role in host preference since damage per individual plant was positively correlated with plant size. Our results suggest that total PA concentration and specifically jacobine had a positive effect on specialist feeding, indicating ecological costs involved in the production of PAs. Ecological costs related to plant secondary compounds could explain why not all individuals produce high levels of these compounds. In addition, differences in specialist herbivore pressures among sites may contribute to the variation in secondary metabolites among populations.
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Do distances among host patches and host density affect the distribution of a specialist parasitoid?
Oecologia, 2005Co-Authors: Sonja Esch, Peter G. L. Klinkhamer, Ed Van Der MeijdenAbstract:The effect of spatial habitat structure and patchiness may differ among species within a multi-trophic system. Theoretical models predict that species at higher trophic levels are more negatively affected by fragmentation than are their hosts or preys. The absence or presence of the higher trophic level, in turn, can affect the population dynamics of lower levels and even the stability of the trophic system as a whole. The present study examines different effects of spatial habitat structure with two field experiments, using as model system the parasitoid Cotesia popularis which is a specialist larval parasitoid of the herbivore Tyria jacobaeae . One experiment examines the colonisation rate of the parasitoid and the percentage parasitism at distances occurring on a natural scale; the other experiment examines the dispersal rate and the percentage parasitism in relation to the density of the herbivore and its host plant. C. popularis was able to reach artificial host populations at distances up to the largest distance created (at least 80 m from the nearest source population). Also, the percentage parasitism did not differ among the distances. The density experiment showed that the total number of herbivores parasitised was higher in patches with a high density of hosts, regardless of the density of the host plant. The percentage parasitism, however, was not related to the density of the host. The density of the host plant did have a (marginally) significant effect on the percentage parasitism, probably indicating that the parasitoid uses the host plant of the herbivore as a cue to find the herbivore itself. In conclusion, the parasitoid was not affected by the spatial habitat structure on spatial scales that are typical of local patches.
Nathan T. Rudd - One of the best experts on this subject based on the ideXlab platform.
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Local Dispersal by the Cinnabar Moth Tyria jacobaeae
Ecological Applications, 1996Co-Authors: Nathan T. Rudd, Peter B. McevoyAbstract:We used mark-recapture data to measure and model movement by the adult stage of the cinnabar moth Tyria jacobaeae (Lepidoptera, Arctiidae). Our objectives were: (1) to standardize the description of cinnabar moth movement and thereby provide a more reliable basis for comparison and extrapolation, and (2) to screen the potential influence of gender, physical condition, time, spatial location, and spatial heterogeneity in the environment on movement parameters. Recapture rates depended on wing wear (low 16%, high 11%) but were independent of behavior immediately after release (mobile 15%, immobile 14%), gender (male 13%, female 16%), or location in the study area (central 15%, peripheral 15%). Thus, mortality and/or emigration was greater for individuals with high wing wear compared to those with low wing wear. Moths were aggregated at the southwest margin of the study area both at initial capture and recapture. The direction of movement was biased in north and south directions, perhaps because forests on the east and west boundaries created a corridor channeling movement. The movement observed within a single generation did not conform to simple diffusion, which predicts that the mean square displacement (MSD) increases linearly with time. Instead, observed movement rates varied over time, and the relationship between MSD and time varied by gender, smoothly decelerating in males and erratically increasing in females. Observed movement (represented by the frequency distribution of displacements x for each time t with time measured at a daily resolution) was adequately approximated by a Weibull distribution, for which estimates of the shape and scale parameters were calculated. Male distributions were more frequently mounded, associated with higher values of the shape parameter α, and the scale of male distributions shifted sooner to longer distances, associated with higher values of the scale parameter β. The Weibull parameters varied by sex and time, suggesting that males were initially more mobile than females, but the magnitude of the difference varied over time. The speed and direction of individual movement were independent of the moth's spatial location within the field. We conclude that (1) movement speed depended on gender and time, while movement direction was related to spatial heterogeneity in the environment, and (2) much of the disagreement about movement rates among studies of the cinnabar moth can be related to researchers taking measurements and drawing inferences on different scales of observation, and therefore arriving at conflicting results.
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effects of vegetation disturbances on insect biological control of tansy ragwort senecio jacobaea
Ecological Applications, 1993Co-Authors: Peter B. Mcevoy, Nathan T. RuddAbstract:Our study had two major objectives: (1) to clarify the roles of buried seed and different types of localized disturbance in activating outbreaks of a pasture weed (tansy ragwort, Senecio jacobaea), and (2) to measure the effectiveness of two natural enemies (the cinnabar moth Tyria jacobaeae and a ragwort flea beetle, Longitarsus jacobaeae) in inhibiting weed population increase and spread. We conducted a 5-yr field experiment on the coast of Oregon using a randomized-block design with four blocks x three levels of disturbance (background vegetation was Tilled, Clipped, Unaltered) x two levels of cin- nabar moth (Exposed, Protected) x two levels of flea beetle (Exposed, Protected) = 48 plots (each plot was 0.25 m2). Disturbance consistently increased ragwort abundance (measured as density of juve- niles, adults, and their offspring; cover; and biomass); the effect was generally greater in Tilled compared to Clipped disturbance treatments. We also found striking differences in the contribution of each natural enemy to ragwort control. The flea beetle quickly reduced ragwort survival, and this led to a strong and rapid reduction in ragwort abundance. The cinnabar moth reduced ragwort fecundity, but this did not translate into reductions in ragwort cover (measured in 1986 and 1987) or biomass (measured annually from 1986 through 1990). These results establish that (1) ragwort populations were limited more by availability of microsites for germination and establishment than by availability of seed, (2) the ragwort flea beetle was the key factor regulating ragwort abundance, and (3) reduction in ragwort fecundity by the cinnabar moth had little effect on the dynamics of ragwort populations on local scales of space and time. These findings underscore the value of field experiments for investigating the dynamics of biological control systems, the manner in which they are regulated, and their response to perturbation. They further establish how colonization and invasion by ragwort depend on attributes of the disturbance and of natural enemy regimes.
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disturbance competition and herbivory effects on ragwort senecio jacobaea populations
Ecological Monographs, 1993Co-Authors: Peter B. Mcevoy, Caroline Cox, Nathan T. Rudd, Manuela HusoAbstract:The balance of forces determining the successful control of ragwort Senecio jacobaea by introduced insects was investigated in a field experiment by manipulating the time of disturbance, the level of interspecific plant competition, and the level of herbivory by the cinnabar moth Tyria jacobaeae and the ragwort flea beetle Longitarsus jacobaeae. We used a factorial design containing 0.25—m2 plots arranged as 4 Blocks × 2 Disturbance Time (plots were tilled in Fall 1986 or Spring 1987) × 3 Plant Competition levels (vegetation other than ragwort was Removed, Clipped, or Unaltered) × 2 Cinnabar Moth levels (Exposed, Protected) × 2 Flea Beetle levels (Exposed, protected). The response of ragwort was measured as colonization, survivorship, and reproduction of the first ragwort generation, establishment of juveniles in the second generation, and changes in ragwort biomass from 1987 through 1990. We also made annual measurements from 1987 through 1990 of the allocation of space (the limiting resource in the Unaltered competition treatment) among the categories ragwort, other species, litter, and open space. Natural enemy responses were characterized by relating variation in the concentration of enemies and the concentration of ragwort among patches. We found that abundant buried seed and localized disturbances combined to activate incipient ragwort outbreaks, and that interspecific plant competition and herbivory by the ragwort flea beetle combined to inhibit the increase and spread of incipient outbreaks. Time of disturbance had little effect on the outcome of biological control. Under conditions in the Removed and Clipped treatments (where there was sufficient open space for germination and establishment), reduction in seed production in the first generation caused by cinnabar moth larvae led to a reduction in plant numbers in the second generation, but caused only a weak effect on ragwort cover and no detectable effect on ragwort biomass over the longer term from 1986 through 1990. At the spatial scale examined, inhibition by the ragwort flea beetle and plant competition took the extreme form of elimination of all ragwort individuals except the pool of seed buried in the soil. Our findings lead us to (1) reject the view that successful biological control leads to a stable pest—enemy equilibrium on a local spatial scale, (2) strongly endorse "search and destroy" and weakly endorse "complementary enemies" strategies suggested by Murdoch et al. (1985) as ways to improve control, and (3) emphasize resource limitation in the pest at low density as a key feature distinguishing biological control of weeds from biological control of insects.
Thomas Hartmann - One of the best experts on this subject based on the ideXlab platform.
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Gustatory responsiveness to pyrrolizidine alkaloids in the Senecio specialist, Tyria jacobaeae (Lepidoptera, Arctiidae)
Physiological Entomology, 2004Co-Authors: Elizabeth A. Bernays, Thomas Hartmann, R. F. ChapmanAbstract:. Electrophysiological recordings from taste sensilla of the caterpillar Tyria jacobaeae with the pyrrolizidine alkaloids, characteristic compounds from their host plants, demonstrated sensitivity of a pyrrolizidine alkaloid-sensitive cell in the lateral galeal sensilla at concentrations as low as 1 × 10−11 M. Another pyrrolizidine alkaloid-sensitive cell in the medial galeal sensilla responded at higher concentrations. Both pyrrolizidine alkaloid-cells were maximally sensitive to seneciphylline N-oxide and senecionine N-oxide. Seven other pyrrolizidine alkaloids were less stimulating. Monocrotaline N-oxide was the least stimulating. Observation experiments demonstrated that differences in sensitivity to different pyrrolizidine alkaloids at the electrophysiological level were correlated with differences in feeding behaviour; the first feeding bout was of longer duration on diet containing seneciphylline N-oxide than on diet containing monocrotaline N-oxide, and a plain diet was generally not accepted.
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evolutionary recruitment of a flavin dependent monooxygenase for the detoxification of host plant acquired pyrrolizidine alkaloids in the alkaloid defended arctiid moth Tyria jacobaeae
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Claudia Naumann, Thomas Hartmann, Dietrich OberAbstract:Larvae of Tyria jacobaeae feed solely upon the pyrrolizidine alkaloid-containing plant Senecio jacobaea. Ingested pyrrolizidine alkaloids (PAs), which are toxic to unspecialized insects and vertebrates, are efficiently N-oxidized in the hemolymph of T. jacobaeae by senecionine N-oxygenase (SNO), a flavin-dependent monooxygenase (FMO) with a high substrate specificity for PAs. Peptide microsequences obtained from purified T. jacobaeae SNO were used to clone the corresponding cDNA, which was expressed in active form in Escherichia coli. T. jacobaeae SNO possesses a signal peptide characteristic of extracellular proteins, and it belongs to a large family of mainly FMO-like sequences of mostly unknown function, including two predicted Drosophila melanogaster gene products. The data indicate that the gene for T. jacobaeae SNO, highly specific for toxic pyrrolizidine alkaloids, was recruited from a preexisting insect-specific FMO gene family of hitherto unknown function. The enzyme allows the larvae to feed on PA-containing plants and to accumulate predation-deterrent PAs in the hemolymph.
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the two faces of pyrrolizidine alkaloids the role of the tertiary amine and its n oxide in chemical defense of insects with acquired plant alkaloids
FEBS Journal, 1997Co-Authors: Rainer Lindigkeit, Andreas Biller, Markus Buch, Hansmartin Schiebel, Michael Boppre, Thomas HartmannAbstract:Larvae of Creatonotos transiens (Lepidoptera, Arctiidae) and Zonocerus variegatus (Orthoptera, Pyr-gomorphidae) ingest 14C-labeled senecionine and its N-oxide with the same efficiency but sequester the two tracers exclusively as N-oxide. Larvae of the non-sequestering Spodoptera littoralis eliminate efficiently the ingested alkaloids. During feeding on the two alkaloidal forms transient levels of senecionine (but not of the N-oxide) are built up in the haemolymph of S. littoralis larvae. Based on these results, senecionine [18O]N-oxide was fed to C. transiens larvae and Z. variegatus adults. The senecionine N-oxide recovered from the haemolymph of the two insects shows an almost complete loss of 18O label, indicating reduction of the orally fed N-oxide in the guts, uptake of the tertiary alkaloid and its re-N-oxidation in the haemolymph. The enzyme responsible for N-oxidation is a soluble mixed function monooxygenase. It was isolated from the haemolymph of the sequestering arctiid Tyria jacobaeue and purified to electrophoretic homogeneity. The enzyme is a flavoprotein with a native M, of 200000 and a subunit M, of 51 000. It shows a pH optimum at 7.0, has its maximal activity at a temperature of 40–45°C and an isoelectric point at pH 4.9. The reaction is strictly NADPH-dependent (Km, 1.3 μM). From 20 pyrrolizidine alkaloids so far tested as substrates, the enyzme N-oxidizes only alkaloids with structural elements which are essential for hepatotoxic and genotoxic pyrrolizidine alkaloids (i.e. 1,2-double bond, esterification of the allylic hydroxyl group, presence of a second free or esterified hydroxyl group at carbon 7). A great variety of related alkaloids and xenobiotics were tested as substrate, none was accepted. The K, values of senecionine, monocrotaline and heliotrine, representing the three main types of pyrrolizidine alkaloids, are 1.3 μM, 12.5 μM and 290 μM, respectively. The novel enzyme was named senecionine N-oxygenase (SNO). The enzyme was partially purified from two other arctiids. The three SNOs show the same general substrate specificity but differ in their affinities towards the main structural types of pyrrolizidine alkaloids. The enzymes from the two generalists (Creatonotos transiens and Arctia caja) display a broader substrate affinity than the enzyme from the specialist (Tyria jacobaeae). The two molecular forms of pyrrolizidine alkaloids, the lipophilic protoxic tertiary amine and its hydrophilic nontoxic N-oxide are discussed in respect to their bioactivation and detoxification in mammals and their role as defensive chemicals in specialized insects. Pyrrolizidine-alkaloid-sequestering insects store the alkaloids as nontoxic N-oxides which are reduced in the guts of any potential insectivore. The lipophilic tertiary alkaloid is absorbed passively and then bioactivated by cytochrome P 450 oxidase.
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The two Faces of Pyrrolizidine Alkaloids: the Role of the Tertiary Amine and its N‐Oxide in Chemical Defense of Insects with Acquired Plant Alkaloids
European journal of biochemistry, 1997Co-Authors: Rainer Lindigkeit, Andreas Biller, Markus Buch, Hansmartin Schiebel, Michael Boppre, Thomas HartmannAbstract:Larvae of Creatonotos transiens (Lepidoptera, Arctiidae) and Zonocerus variegatus (Orthoptera, Pyr-gomorphidae) ingest 14C-labeled senecionine and its N-oxide with the same efficiency but sequester the two tracers exclusively as N-oxide. Larvae of the non-sequestering Spodoptera littoralis eliminate efficiently the ingested alkaloids. During feeding on the two alkaloidal forms transient levels of senecionine (but not of the N-oxide) are built up in the haemolymph of S. littoralis larvae. Based on these results, senecionine [18O]N-oxide was fed to C. transiens larvae and Z. variegatus adults. The senecionine N-oxide recovered from the haemolymph of the two insects shows an almost complete loss of 18O label, indicating reduction of the orally fed N-oxide in the guts, uptake of the tertiary alkaloid and its re-N-oxidation in the haemolymph. The enzyme responsible for N-oxidation is a soluble mixed function monooxygenase. It was isolated from the haemolymph of the sequestering arctiid Tyria jacobaeue and purified to electrophoretic homogeneity. The enzyme is a flavoprotein with a native M, of 200000 and a subunit M, of 51 000. It shows a pH optimum at 7.0, has its maximal activity at a temperature of 40–45°C and an isoelectric point at pH 4.9. The reaction is strictly NADPH-dependent (Km, 1.3 μM). From 20 pyrrolizidine alkaloids so far tested as substrates, the enyzme N-oxidizes only alkaloids with structural elements which are essential for hepatotoxic and genotoxic pyrrolizidine alkaloids (i.e. 1,2-double bond, esterification of the allylic hydroxyl group, presence of a second free or esterified hydroxyl group at carbon 7). A great variety of related alkaloids and xenobiotics were tested as substrate, none was accepted. The K, values of senecionine, monocrotaline and heliotrine, representing the three main types of pyrrolizidine alkaloids, are 1.3 μM, 12.5 μM and 290 μM, respectively. The novel enzyme was named senecionine N-oxygenase (SNO). The enzyme was partially purified from two other arctiids. The three SNOs show the same general substrate specificity but differ in their affinities towards the main structural types of pyrrolizidine alkaloids. The enzymes from the two generalists (Creatonotos transiens and Arctia caja) display a broader substrate affinity than the enzyme from the specialist (Tyria jacobaeae). The two molecular forms of pyrrolizidine alkaloids, the lipophilic protoxic tertiary amine and its hydrophilic nontoxic N-oxide are discussed in respect to their bioactivation and detoxification in mammals and their role as defensive chemicals in specialized insects. Pyrrolizidine-alkaloid-sequestering insects store the alkaloids as nontoxic N-oxides which are reduced in the guts of any potential insectivore. The lipophilic tertiary alkaloid is absorbed passively and then bioactivated by cytochrome P 450 oxidase.
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Pyrrolizidine alkaloids between plants and insects: A new chapter of an old story
CHEMOECOLOGY, 1994Co-Authors: Thomas HartmannAbstract:Among alkaloids the pyrrolizidine alkaloids (PAs) play a unique role in the interactions between plants and adapted insects. In Senecio spp. (Asteraceae) PAs are synthesized in the roots as alkaloid N -oxides which are specifically translocated into shoots via the phloem-path and channeled to the preferred sites of storage ( e.g. inflorescences) where they are stored in the cell vacuoles. In different Senecio spp. senecionine N -oxide is produced as the common product of biosynthesis, which subsequently via a number of simple but specific reactions is transformed into typical speciesspecific PA-patterns. Insects from diverse taxa sequester PAs for their own defense. Lepidopterans ( e.g. arctiids such as Tyria jacobaeae and Creatonotos transiens ) may hydrolyze plant acquired ester-PAs and convert the resulting necine base into insect-specific PAs by esterification with an acid of their own metabolism. Adapted arctiids and the grasshopper Zonocerus take up PAs in the state of the tertiary amine. N -Oxides are reduced in the guts prior to uptake. In the bodies the tertiary PAs are rapidly N -oxidized by a specific mixed-function oxigenase and are maintained in the N -oxide state. The importance of the reversible interconversion of the nontoxic N -oxide (pro-toxine) into the toxic tertiary alkaloid is discussed as the specific feature of PAs in plant-insect interactions.
