Jörg Samietz

University of Veracruz, Veracruz, Estado de Veracruz-Llave, Mexico

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Publications (39)49.98 Total impact

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    ABSTRACT: We examined the attack of a potentially invasive tropical insect on a non-optimal temperate zone host and tested the hypothesis that variation in plant secondary metabolites and/or locally-grown host plant cultivars could shape agroecosystem resilience in a region undergoing climatic change. We studied the phytophagous fruit fly Anastrepha ludens (Diptera: Tephritidae) and 18 apple cultivars most of which vary significantly in total content of phenolic compounds. High content of phenolic compounds significantly increased egg or larval mortality whereas cultivars exhibiting low content were severely infested. Intermediate concentrations resulted in pupal malformation and delayed immature development. These results provide a valuable insight into biotic factors that contribute to environmental resilience to an invasive species that could expand its geographical range in response to global climate change. They also highlight the importance of protecting ancestral or locally-grown apple cultivars as sources of genes for breeding programs directed at restoring the ability of crops to defend themselves against emerging pests or to cope with changing environmental conditions.
    Agriculture Ecosystems & Environment 01/2014; 186:54–63. · 2.86 Impact Factor
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    ABSTRACT: BACKGROUND: Rapid and reliable identification of quarantine pests is essential for plant inspection services to prevent introduction of invasive species. For insects, this may be a serious problem when dealing with morphologically similar cryptic species complexes and early developmental stages that lack distinctive characters useful for taxonomic identification. DNA based barcoding could solve many of these problems. The standard barcode fragment, an approx. 650 base pairs long sequence of the 5[prime]end of the mitochondrial cytochrome oxidase I (COI), enables differentiation of a very wide range of arthropods. However, problems remain in some taxa, such as Tephritidae, where recent genetic differentiation among some of the described species hinders accurate molecular discrimination. RESULTS: In order to explore the full species discrimination potential of COI, we sequenced the barcoding region of the COI gene of a range of economically important Tephritid species and complemented these data with all GenBank and BOLD entries for the systematic group available as of January 2012. We explored the limits of species delimitation of this barcode fragment among 193 putative Tephritid species and established operational taxonomic units (OTUs), between which discrimination is reliably possible. Furthermore, to enable future development of rapid diagnostic assays based on this sequence information, we characterized all single nucleotide polymorphisms (SNPs) and established "near-minimal" sets of SNPs that differentiate among all included OTUs with at least three and four SNPs, respectively. CONCLUSIONS: We found that although several species cannot be differentiated based on the genetic diversity observed in COI and hence form composite OTUs, 85% of all OTUs correspond to described species. Because our SNP panels are developed based on all currently available sequence information and rely on a minimal pairwise difference of three SNPs, they are highly reliable and hence represent an important resource for developing taxon-specific diagnostic assays. For selected cases, possible explanations that may cause composite OTUs are discussed.
    BMC Evolutionary Biology 05/2013; 13(1):106. · 3.29 Impact Factor
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    ABSTRACT: Given the repercussions of pests and diseases on agricultural production, detailed forecasting tools have been developed to simulate the degree of infestation depending on actual weather conditions. The life cycle of pests is most successfully predicted if the micro-climate of the immediate environment (habitat) of the causative organisms can be simulated. Sub-seasonal pest forecasts therefore require weather information for the relevant habitats and the appropriate time scale. The pest forecasting system SOPRA (www.sopra.info) currently in operation in Switzerland relies on such detailed weather information, using hourly weather observations up to the day the forecast is issued, but only a climatology for the forecasting period. Here, we aim at improving the skill of SOPRA forecasts by transforming the weekly information provided by ECMWF monthly forecasts (MOFCs) into hourly weather series as required for the prediction of upcoming life phases of the codling moth, the major insect pest in apple orchards worldwide. Due to the probabilistic nature of operational monthly forecasts and the limited spatial and temporal resolution, their information needs to be post-processed for use in a pest model. In this study, we developed a statistical downscaling approach for MOFCs that includes the following steps: (i) application of a stochastic weather generator to generate a large pool of daily weather series consistent with the climate at a specific location, (ii) a subsequent re-sampling of weather series from this pool to optimally represent the evolution of the weekly MOFC anomalies, and (iii) a final extension to hourly weather series suitable for the pest forecasting model. Results show a clear improvement in the forecast skill of occurrences of upcoming codling moth life phases when incorporating MOFCs as compared to the operational pest forecasting system. This is true both in terms of root mean squared errors and of the continuous rank probability scores of the probabilistic forecasts vs. the mean absolute errors of the deterministic system. Also, the application of the climate conserving recalibration (CCR, Weigel et al. 2009) technique allows for successful correction of the under-confidence in the forecasted occurrences of codling moth life phases. Reference: Weigel, A. P.; Liniger, M. A. & Appenzeller, C. (2009). Seasonal Ensemble Forecasts: Are Recalibrated Single Models Better than Multimodels? Mon. Wea. Rev., 137, 1460-1479.
    04/2012;
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    ABSTRACT: Monthly weather forecasts (MOFCs) were shown to have skill in extratropical continental regions for lead times up to 3 weeks, in particular for temperature and if weekly averaged. This skill could be exploited in practical applications for implementations exhibiting some degree of memory or inertia toward meteoro-logical drivers, potentially even for longer lead times. Many agricultural applications fall into these categories because of the temperature-dependent development of biological organisms, allowing simulations that are based on temperature sums. Most such agricultural models require local weather information at daily or even hourly temporal resolution, however, preventing direct use of the spatially and temporally aggregated in-formation of MOFCs, which may furthermore be subject to significant biases. By the example of forecasting the timing of life-phase occurrences of the codling moth (Cydia pomonella), which is a major insect pest in apple orchards worldwide, the authors investigate the application of downscaled weekly temperature anomalies of MOFCs for use in an impact model requiring hourly input. The downscaling and postprocessing included the use of a daily weather generator and a resampling procedure for creating hourly weather series and the application of a recalibration technique to correct for the original underconfidence of the forecast occurrences of codling moth life phases. Results show a clear skill improvement of up to 3 days in root-mean-square error over the full forecast range when incorporating MOFCs as compared with deterministic benchmark forecasts using climatological information for predicting the timing of codling moth life phases.
    Journal of Applied Meteorology and Climatology 01/2012; 51(9):1633-1638. · 2.02 Impact Factor
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    ABSTRACT: Global warming will lead to earlier beginnings and prolongation of growing seasons in temperate regions and will have pronounced effects on phenology and life-history adaptation in many species. These changes were not easy to simulate for actual phenologies because of the rudimentary temporal (season) and spatial (regional) resolution of climate model projections. We investigate the effect of climate change on the regional incidence of a pest insect with nearly worldwide distribution and very high potential for adaptation to season length and temperature--the Codling Moth, Cydia pomonella. Seasonal and regional climate change signals were downscaled to the hourly temporal scale of a pest phenology model and the spatial scale of pest habitats using a stochastic weather generator operating at daily scale in combination with a re-sampling approach for simulation of hourly weather data. Under future conditions of increased temperatures (2045-2074), the present risk of below 20% for a pronounced second generation (peak larval emergence) in Switzerland will increase to 70-100%. The risk of an additional third generation will increase from presently 0-2% to 100%. We identified a significant two-week shift to earlier dates in phenological stages, such as overwintering adult flight. The relative extent (magnitude) of first generation pupae and all later stages will significantly increase. The presence of first generation pupae and later stages will be prolonged. A significant decrease in the length of overlap of first and second generation larval emergence was identified. Such shifts in phenology may induce changes in life-history traits regulating the life cycle. An accordingly life-history adaptation in photoperiodic diapause induction to shorter day-length is expected and would thereby even more increase the risk of an additional generation. With respect to Codling Moth management, the shifts in phenology and voltinism projected here will require adaptations of plant protection strategies to maintain their sustainability.
    PLoS ONE 01/2012; 7(4):e35723. · 3.73 Impact Factor
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    ABSTRACT: The walnut husk fly, Rhagoletis completa Cresson (Diptera: Tephritidae), has recently invaded Switzerland, Austria, Germany, and France, probably crossing the alpine divide after its initial introduction into Italy. Here, the susceptibility of 36 walnut [Juglans regia L. (Juglandaceae)] cultivars to attack by R. completa was studied in an experimental orchard in Switzerland. Walnut cultivars differed significantly in infestation rates; cultivars that produced large, heavy fruit harboured significantly more larvae than cultivars that produced smaller fruit. Pupal weight was significantly influenced by cultivar, but not by any of the physical properties that we measured. For individual fruit within a cultivar, pupal weight was weakly related to fruit weight and infestation level. Adult longevity was correlated with pupal weight and appeared to be favoured in flies that developed in large-fruit cultivars. The longevities of adults recovered from different cultivars differed significantly. The shortest longevity was recorded for flies recovered from Geisenheim 1049 (39.2 ± 2.80 days) and the longest for flies recovered from Sheinovo (68.8 ± 21.75 days). Differences in diapause length were also highly significant and varied between 167 ± 5.1 (Esterhazy III) and 257.4 ± 8.21 days (Mayette). These results suggest that (1) across and within cultivars, walnut husk flies prefer to infest (i.e., they develop better in) large, heavy fruit, and (2) offspring that develop in large fruit are likely to accrue fitness advantages over the offspring of females using smaller fruit. Our results provide the basis for subsequent studies on resource defence by males, as they enable a prediction of which type of fruit males should defend more vigorously.
    Entomologia Experimentalis et Applicata 08/2011; 140(3):207 - 217. · 1.71 Impact Factor
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    ABSTRACT: The Walnut Husk Fly, Rhagoletis completa Cresson (Diptera: Tephritidae), is native to North America (Midwestern US and north-eastern Mexico) and has invaded several European countries in the past decades by likely crossing the alpine divide separating most parts of Switzerland from Italy. Here, we determined its current distribution in Switzerland by sampling walnuts (Juglans regia L.) in ecologically and climatically distinct regions along potential invasion corridors. R. completa was found to be firmly established in most low altitude areas of Switzerland where walnuts thrive, but notably not a single parasitoid was recovered from any of the samples. Infested fruit was recovered in 42 of the 71 localities that were surveyed, with mean fruit infestation rate varying greatly among sites. The incidence of R. completa in Switzerland is closely related to meteorological mean spring temperature patterns influencing growing season length, but not to winter temperatures, reflecting survival potential during hibernation. Importantly, areas in which the fly is absent correspond with localities where the mean spring temperatures fall below 7°C. Historical data records show that the natural cold barrier around the Alpine divide in the central Swiss Alps corresponding to such minimal temperatures has shrunk significantly from a width of more than 40 km before 1990 to around 20 km after 2000. We hypothesize on possible invasion/expansion routes along alpine valleys, dwell on distribution patterns in relation to climate, and outline future research needs as the incursion of R. completa into Switzerland; and, more recently, other European countries, such as Germany, Austria, France and Slovenia, represent an example of alien species that settle first in the Mediterranean Basin and from there become invasive by crossing the Alps.
    Bulletin of entomological research 02/2011; 101(4):451-65. · 1.99 Impact Factor
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    ABSTRACT: As a consequence of current and projected climate change in temperate regions of Europe, agricultural pests and diseases are expected to occur more frequently and possibly to extend to previously not affected regions. Given their economic and ecological relevance, detailed forecasting tools for various pests and diseases have been developed, which model their phenology depending on actual weather conditions and suggest management decisions on that basis. Assessing the future risk of pest-related damages requires future weather data at high temporal and spatial resolution. Here, we use a combined stochastic weather generator and re-sampling procedure for producing site-specific hourly weather series representing present and future (1980-2009 and 2045-2074 time periods) climate conditions in Switzerland. The climate change scenarios originate from the ENSEMBLES multi-model projections and provide probabilistic information on future regional changes in temperature and precipitation. Hourly weather series are produced by first generating daily weather data for these climate scenarios and then using a nearest neighbor re-sampling approach for creating realistic diurnal cycles. These hourly weather series are then used for modeling the impact of climate change on important life phases of the codling moth and on the number of predicted infection days of fire blight. Codling moth (Cydia pomonella) and fire blight (Erwinia amylovora) are two major pest and disease threats to apple, one of the most important commercial and rural crops across Europe. Results for the codling moth indicate a shift in the occurrence and duration of life phases relevant for pest control. In southern Switzerland, a rd generation per season occurs only very rarely under today's climate conditions but is projected to become normal in the 2045-2074 time period. While the potential risk for a rd generation is also significantly increasing in northern Switzerland (for most stations from roughly 1 % on average today to over 60 % in the future for the median climate change signal of the multi-model projections), the actual risk will critically depend on the pace of the adaptation of the codling moth with respect to the critical photoperiod. To control this additional generation, an intensification and prolongation of control measures (e.g., insecticides) will be required, implying an increasing risk of pesticide resistances. For fire blight, the projected changes in infection days are less certain due to uncertainties in the leaf wetness approximation and the simulation of the blooming period. Two compensating effects are projected, warmer temperatures favoring infections are balanced by a temperature-induced advancement of the blooming period, leading to no significant change in the number of infection days under future climate conditions for most stations.
    Earth System Dynamics Discussions  01/2011;
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    ABSTRACT: As a consequence of current and projected climate change in temperate regions of Europe, agricultural pests and diseases are expected to occur more frequently and possibly to extend to previously unaffected regions. Given their economic and ecological relevance, detailed forecasting tools for various pests have been developed, which model the infestation depending on actual weather conditions. Assessing the future risk of pest-related damages therefore requires future weather data at high temporal and spatial resolution. In particular, pest forecast models are often not based on screen temperature and precipitation alone (i.e., the most generally projected climate variables), but might require input variables such as soil temperature, in-canopy net radiation or leaf wetness. Here, we use a stochastic weather and a re-sampling procedure for producing site-specific hourly weather data from regional climate change scenarios for 2050 in Switzerland. The climate change scenarios were derived from multi-model projections and provide probabilistic information on future regional changes in temperature and precipitation. Hourly temperature, precipitation and radiation data were produced by first generating daily weather data for these climate scenarios and then using a nearest neighbor re-sampling approach for creating realistic diurnal cycles. These hourly weather time series were then used for modeling important phases in the lifecycle of codling moth, the major insect pest in apple orchards worldwide. First results indicate a shift in the occurrence and duration of phases relevant for pest disease control for projected as compared to current climate (e.g. the flight of the codling moth starts about ten days earlier in future climate), continuing an already observed trend towards more favorable conditions for this insect during the last 20 years.
    09/2010;
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    ABSTRACT: Apple crop protection mainly relies on pesticides although several alternative pest management strategies being available. This is largely caused by the problem that multiple environmental and economic aspects are to consider simultaneously, hiding if one strategy is more sustainable than another. In our study we investigated the elements that need to be considered in order to reach transparency upon the overall result of the sustainability assessment. We present a system description tool created specially for data collection required by life cycle assessment, environmental risk assessment and full cost calculations. Using the various results from these assessments as qualitative attributes we designed a multicriteria tool that allows us to aggregate sustainability attributes over five levels to an overall sustainability rating. An example, assessing different crop protection systems of apple production, demonstrates the transparency of this method. We conclude that rating scales and decision rules might substantially influence the overall sustainability rating. Therefore, the definition of rating scales and decision rules should be carefully set and discussed among the research teams. In our case experts have participated from five European countries being partner of the EU-FP6 project ENDURE.
    08/2010;
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    ABSTRACT: Codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), is an important pest of pome fruit and walnut orchards throughout the world and the respective key pest in Bulgaria. Codling moth resistance to many insecticides has been recently detected in Bulgaria. As part of anti-resistance strategy mating disruption with Isomate C plus dispensers (ShinEtsu, Japan) was tested against codling moth (CM) in the two consecutive years 2006 and 2007. In both years Isomate-C plus dispensers inhibited completely the CM captures in the pheromone traps installed in the experimental plot. This indicated that mating disruption was very successful. Before harvest, damage stayed there at in a low level - 0.06% in 2006 and 0.5% in 2007. As comparison in the conventionally treated orchard, eleven to fifteen treatments (17-23 active ingredients) were applied during the season to control CM, leaf miners, leaf rollers and San Jose scale. Eight to fourteen of them (14-21 active ingredients) were timed against codling moth. In spite of that, fruit damage before harvest reached 3.4% in 2006 and 5.2 in 2007. The overwintering population in autumn 2006 reached 1.1 larvae per tree, but increased to 3.3 larvae per tree in 2007. CM population in the conventionally treated orchard was apparently resistant The results of this investigation will open the possibilities for usage of the pheromone dispensers as an alternative measure to control codling moth in Bulgaria. This should promote ecological fruit products and preservation of the natural environment, in accordance with the European standards for integrated fruit production. The studies are being continued.
    01/2009;
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    ABSTRACT: The pupal parasitoid Pimpla turionellae (L.) uses self-produced vibrations transmitted on the plant substrate, so-called vibrational sounding, to locate immobile concealed pupal hosts. The wasps are able to use vibrational sounding reliably over a broad range of ambient temperatures and even show an increased signal frequency and intensity at low temperatures. The present study investigates how control of body temperature in the wasps by endothermic mechanisms may facilitate host location under changing thermal environments. Insect body temperature is measured with real-time IR thermography on plant-stem models at temperature treatments of 10, 18, 26 and 30 °C, whereas behaviour is recorded with respect to vibrational host location. The results reveal a low-level endothermy that likely interferes with vibrational sound production because it occurs only in nonsearching females. At the lowest temperature of 10 °C, the thoracic temperature is 1.15 °C warmer than the ambient surface temperature whereas, at the high temperatures of 26 and 30 ° C, the wasps cool down their thorax by 0.29 and 0.47 °C, respectively, and their head by 0.45 and 0.61 °C below ambient surface temperature. By contrast, regardless of ambient temperature, searching females always have a slightly elevated body temperature of at most 0.30 °C above the ambient surface temperature. Behavioural observations indicate that searching females interrupt host location more frequently at suboptimal temperatures, presumably due to the requirements of thermoregulation. It is assumed that both mechanisms, producing vibrations for host location and low-level endothermy, are located in the thorax. Endothermy by thoracic muscle work probably disturbs signal structure of vibrational sounding, so the processes cannot be used at the same time.
    Physiological Entomology 03/2008; 33(1):17-24. · 1.42 Impact Factor
  • Journal of Plant Protection Research 01/2008; 48(4):509-513.
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    ABSTRACT: The forecasting tool SOPRA has been developed with the objective of optimizing timing of monitoring, management and control measures of insect pests in fruit orchards in Switzerland. Applying time-varying distributed delay approaches, phenology-models were developed driven by solar radiation, air temperature and soil temperature on hourly basis. Relationships between temperature and stage-specific development rates for relevant stages of the life cycles were estab-lished under controlled laboratory conditions for Dysaphis plantaginea , Hoplocampa testudinea , Cydia pomonella , Grapholita lobarzewskii , Cacopsylla pyri , Rhagoletis cerasi , Anthonomus pomorum and Adoxophyes orana . The implementation of body temperatures in the models is based on habitat selection and biophysical modelling of habitat conditions. In order to validate modelling, phenology predictions were compared with several years of independent field observations. On the basis of local weather data, the age structure of the pest populations is simulated and crucial events for management activities are announced. Through a web interface, the simulation results are made available to consultants and growers (www.sopra.info) and the latter can be applied as a decision support system for the eight major insect pests of fruit orchards in the alpine valleys and north of the Alps on local and regional scale.
    Bulletin OEPP/EPPO Bulletin 07/2007; 37:255-260.
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    Stefan Kroder, Jörg Samietz, Silvia Dorn
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    ABSTRACT: Parasitoid host location in nature is facilitated by simultaneously using different information sources. How multisensory orientation on the same spatial scale is influenced by environmental conditions is however poorly understood. Here we test whether changes in reliability of cues can cause parasitoids to alter multisensory orientation and to switch to cues that are more reliable under extreme temperatures. In the ichneumonid wasp Pimpla turionellae, multisensory use of thermally insensitive vision and thermally sensitive mechanosensory host location by vibrational sounding (echolocation on solid substrate) was investigated with choice experiments on plant-stem models under optimum temperature (18 degrees C), at high- (28 degrees C) and low-temperature limits (8 degrees C) of vibrational sounding. Temperature affected relative importance of vibrational sounding whereas visual orientation did not vary. At 18 degrees C, parasitoids used visual and vibrational cues with comparable relative importance. At 8 and 28 degrees C, the role of vibrational sounding in multisensory orientation was significantly reduced in line with decreased reliability. Wasps nearly exclusively chose visual cues at 8 degrees C. The parasitoids switch between cues and sensory systems depending on temperature. As overall precision of ovipositor insertions was not affected by temperature, the parasitoids fully compensate the loss of one cue provided another reliable cue is available on the same spatial scale.
    Journal of Comparative Physiology 03/2007; 193(2):223-31. · 1.86 Impact Factor
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    ABSTRACT: Based on the model system of Brussels sprouts [ Brassica oleracea var. gemmifera (Brassicaceae)], the herbivore cabbage white caterpillar, Pieris brassicae (L.) (Lepidoptera: Pieridae), and the parasitoid wasp, Cotesia glomerata (L.) (Hymenoptera: Braconidae), the influence of plant damage type, and damage duration were assessed on plant volatile emission and subsequent recruitment of natural antagonists of the herbivore. Plants were damaged by three methods for a period of either 3 or 8 h: herbivore damage (HD), progressive mechanical damage, and final mechanical damage inflicted in a single event. Wind-tunnel bioassays evaluated whether the mode of damage affected female parasitoid oriented flight. After both periods of damage, all treatments were highly significantly preferred by naïve C. glomerata to undamaged control plants. After 3 h, herbivore-damaged plants were significantly preferred to plants with final damage (FD). Most remarkably, following 8-h damage, the parasitoid preferred both herbivore-damaged and progressively damaged plants to plants with FD and did not significantly discriminate between herbivore and progressively damaged plants, thus indicating a similarity in plant response to herbivore and progressive mechanical damage. In addition to wind-tunnel bioassays, emitted plant volatiles were collected and analysed by thermal desorption gas chromatography/mass spectrometry, following 3 and 8 h of damage in order to correlate volatiles released from different damage types with the attraction of the parasitoid. Differences in volatile profiles from all damage types were similar following both 3 and 8 h of damage, with only (Z)-3-hexenyl acetate found to be emitted in significantly higher quantities by final mechanical damage compared with HD after 3 h. In conclusion, the plant's response to progressive mechanical damage was more similar to HD than final mechanical damage deployed at a single point in time, irrespective of damage duration, and C. glomerata did not significantly discriminate between progressive damage and HD.
    Entomologia Experimentalis et Applicata 01/2007; 125:145-155. · 1.71 Impact Factor
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    ABSTRACT: Abstract Certain ichneumonid parasitoids (Hymenoptera) use self-produced vibrations transmitted on plant substrate, so-called vibrational sounding, to locate their immobile concealed pupal hosts. An ambient temperature dependency with higher frequencies and intensities at higher temperatures is postulated because signals are of myogenic origin. Here, temperature influence on vibratory signals is analysed in the temperate parasitoid Pimpla turionellae under different thermal conditions using plant-stem models to elicit host-searching behaviour. Signals are measured with laser Doppler vibrometry and analysed for time parameters and frequency components applying fast-Fourier transformations. The results reveal an unexpected effect of ambient temperature on signals produced by the female wasps. Although average values of time parameters (pulse trains, pulse train periods, inter pulse duration) are unchanged by ambient temperature, the frequency parameters show an inverse thermal effect. Within the temperature range tested (8–26 °C), decreasing temperature leads to significantly higher frequency and intensity of the self-produced vibrations in the temperate species. This inverse thermal effect may be explained by a temperature-coupled signal production in the frequency domain to compensate negative low-temperature effects on the mechanoreceptors by increased muscle activity. The option of heterothermy to produce signals reliably during vibrational sounding under low temperature is also discussed.
    Physiological Entomology 11/2006; 32(2):105 - 112. · 1.42 Impact Factor
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    STEFAN KRODER, JÖRG SAMIETZ, SILVIA DORN
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    ABSTRACT: Abstract Several parasitic wasps of the Pimplinae (Ichneumonidae) use self-produced vibrations transmitted through plant substrate to locate their concealed immobile hosts (lepidopteran pupae) by reflected signals. This mechanosensory mechanism of host location, called vibrational sounding, depends on the physical characteristics of the plant substrate and the wasp’s body and is postulated to depend on ambient temperature. Adaptations of two parasitoid species to thermal conditions of their habitats and the influence of temperature on the trophic interaction during host location are investigated in the tropical Xanthopimpla stemmator (Thunberg) and compared with the temperate Pimpla turionellae (L.). Plant-stem models with hidden host mimics are offered to individual wasps under defined temperature treatments and scored for the number and location of ovipositor insertions. Significant effects of temperature are found on host-location activity and its success. The tropical species possesses an optimum temperature range for vibrational sounding between 26 and 32 °C, whereas the performance decreases both at low and high temperatures. The temperate species reveals substantial differences with respect to performance at the same thermal conditions. With increasing temperature, P. turionellae shows a reduced response to the host mimic, reduced numbers of ovipositor insertions, and decreased precision of mechanosensory host location. In the tropical X. stemmator, the female wasps are able to locate their host with high precision over a broad range of ambient temperatures, which suggests endothermic thermoregulation during vibrational sounding. Environmental physiology may therefore play a key role in adaptation of the host location mechanism to climatic conditions of the species’ origin.
    Physiological Entomology 08/2006; 31(3):299 - 305. · 1.42 Impact Factor
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    B. Graf, H.U. Höpli, H. Höhn, J. Samietz
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    ABSTRACT: The development of Dysaphis plantaginea (Pass.) (Homoptera: Aphididae) winter eggs was studied at six different constant temperatures ranging from 7.5 to 16.5 °C in order to improve the basis for phenological forecasts in early spring. The mortality was generally low at temperatures below 13.5 °C but increased considerably at 16.5 °C. The effect of temperature on development rates could be described with linear regression within the temperature range under study. The lower temperature threshold for development was estimated to be 4.0 °C and the thermal constant 140 day-degrees. A time-varying distributed delay approach was used to establish a temperature driven phenology model for winter egg hatch of D. plantaginea considering the intrinsic variability in development time. The model parameters such as temperature-dependent development times and corresponding variances were quantified based on the experimental data. When compared with independent observations on egg hatch under semifield conditions, the model gave satisfactory validation results. It can be used as forecasting tool for the optimal timing of monitoring and control measures for D. plantaginea in early spring.
    Entomologia Experimentalis et Applicata 05/2006; 119(3):207 - 211. · 1.71 Impact Factor
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    J Samietz, S Kroder, D Schneider, S Dorn
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    ABSTRACT: Certain parasitic wasps (Ichneumonidae, Pimplinae) use self-produced vibrations transmitted on plant substrate to locate their immobile concealed hosts (i.e. lepidopteran pupae). This mechanosensory mechanism, called the vibrational sounding, depends both on physical cues of the environment and physical activity of the parasitoid and is postulated to depend on ambient temperature. We analysed the influences of temperature on vibrational sounding by choice experiments using plant-stem models with hidden host mimics in the temperate species Pimpla turionellae. The results show a significant effect of temperature on host-location activity and on the success of this process. Outside an optimum range, the performance of the wasps decreased both at low and high temperatures. Below 10 degrees C and beyond 24 degrees C, the wasps displayed (1) substantial reduction in responsiveness, i.e. proportion of females showing ovipositor insertions, (2) reduction of quantitative activity with ovipositor insertions in the individuals, and (3) reduced precision of mechanosensory host location. Nevertheless, female wasps were able to locate their host over a surprisingly broad range of ambient temperatures which indicates that the wasps are able to compensate for temperature effects on vibrational sounding.
    Journal of Comparative Physiology 03/2006; 192(2):151-7. · 1.86 Impact Factor

Publication Stats

244 Citations
49.98 Total Impact Points

Institutions

  • 2011
    • University of Veracruz
      • Instituto de Neuroetología
      Veracruz, Estado de Veracruz-Llave, Mexico
    • Institute of Ecology INECOL
      Heroica Veracruz, Veracruz-Llave, Mexico
  • 2008
    • Karl-Franzens-Universität Graz
      • Institute of Zoology
      Gratz, Styria, Austria
  • 2005
    • Friedrich-Schiller-University Jena
      • Institut für Ökologie
      Jena, Thuringia, Germany
  • 2002
    • ETH Zurich
      Zürich, Zurich, Switzerland