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Otto Schmidt - One of the best experts on this subject based on the ideXlab platform.
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Factors affecting growth in the koinobiont endoparasitoid Venturia canescens in the flour moth Ephestia kuehniella.
Journal of insect physiology, 2007Co-Authors: M. Mahbubur Rahman, Harry L.s. Roberts, Otto SchmidtAbstract:With resistance of insect pests to synthetic pesticides on the increase, the role of parasitoid wasps as biological control agents is expanding in pest and resistance management strategies. One of the predictors of reproductive success of endoparasitoids is the relative size of the wasp at host emergence. While in idiobiont parasitoids, where the host stops feeding after parasitism, the wasp size is determined by the host size at the time of parasitism; the size of koinobiont wasps, where the host continues to feed after parasitism, is dependent on additional factors. Here we show that the host mass and temperature are important factors that determine survival and development of the koinobiont endoparasitoid Venturia canescens in late instar larvae of the flour moth Ephestia kuehniella.
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An empirical model of the sympatric coexistence of two strains of the endoparasitoid wasp Venturia canescens.
Archives of insect biochemistry and physiology, 2006Co-Authors: Harry L.s. Roberts, Michael A. Keller, Otto SchmidtAbstract:Recent research has demonstrated that a laboratory culture of the asexual solitary endoparasitoid wasp Venturia canescens Grav. (Hymenoptera: Ichneumonidae) contains two genetically and phenotypically distinct lines, coexisting on their host the flour moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). The basis to the coexistence of the two lines appears to be differences in their reproductive success under single parasitism and superparasitism. Furthermore, examination of field-derived wasps from several locations has shown that the phenotypes displayed by the laboratory colonies also co-occur in field populations. Historically, the impossibility of showing that two species do not occupy separate niches has precluded any demonstration of sympatric coexistence in the field. Here we present the results of an iterative model that uses a range of experimental life history data to predict the stable composition of a mixed population of two lines displaying the laboratory phenotypes under different rates of superparasitism. The model predicts that sympatric coexistence of the two lines is possible when the overall rate of superparasitism is between 4 and 12% or greater. These values are within the rates reported for other solitary endoparasitoid wasp species in the field, and so demonstrate that the sympatric coexistence under natural conditions of two species that display the phenotypes observed in the laboratory lines is, in principle, possible.
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Phenoloxidase-like activities and the function of virus-like particles in ovaries of the parthenogenetic parasitoid Venturia canescens.
Journal of insect physiology, 2005Co-Authors: Otto Schmidt, Markus H. Beck, Wanja Kinuthia, Judy Bellati, Harry L.s. RobertsAbstract:The ichneumonid endoparasitoid Venturia canescens successfully develops inside the hemocoel of another insect by using maternal protein secretions, including nucleic acid-free virus-like particles (VLPs), to manipulate host physiology. These VLPs consist of four major proteins, which are produced mainly in the calyx tissue and transferred into the host insect together with the egg. One of the protein-coding genes (vlp1), with similarities to phospholipid-hydroperoxide glutathione peroxidases (PHGPx), exists in allelic forms producing two protein variants with different protein properties. Here, we summarise observations indicating that oocytes and eggs are the source of reactive electrons, which potentially damage the lining and membranes of calyx tissues. We discuss the possible role of VLP1 in counteracting the damaging effects of oxidised phospholipids on membranes surrounding VLPs in the calyx lumen.
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The development of the endoparasitoid Venturia canescens in Bt-tolerant, immune induced larvae of the flour moth Ephestia kuehniella.
Journal of Invertebrate Pathology, 2004Co-Authors: M. Mahbubur Rahman, Harry L.s. Roberts, Otto SchmidtAbstract:We examined the survival and development of the endoparasitoid Venturia canescens in a Bt-tolerant laboratory strain of the flour moth Ephestia kuehniella, in which Bt-tolerance has been shown to be associated with an inducible elevation of the insect's immune response. The results indicate the elevated immune status associated with Bt-tolerance does not confer cross-protection against parasitism by V. canescens. No significant difference was observed in the rate of emergent wasps from parasitised Bt-tolerant and Bt-susceptible hosts. In addition, wasps from Bt-tolerant hosts had longer development times and were larger than wasps from Bt-susceptible hosts.
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The development of the endoparasitoid wasp Venturia canescens in superparasitised Ephestia kuehniella.
Journal of insect physiology, 2004Co-Authors: Harry L.s. Roberts, Oliver True, Otto SchmidtAbstract:Using a molecular marker that allows the differentiation of two strains of the solitary endoparasitoid wasp Venturia canescens, the study investigated the influence of host mass and the time interval between ovipositions on the survival and development of larvae from both the first and second laid eggs in superparasitised Ephestia kuehniella. As the time interval between ovipositions increased both overall and superparasitism success decreased, however, time between, and order of, ovipositions had little effect on other developmental parameters. Adult size increased with host mass under both parasitism and superparasitism, while host mortality decreased with host mass under superparasitism. In addition, wasps emerging from superparasitised hosts were larger than wasps from parasitised hosts. The results confirm that for V. canescens on the host E. kuehniella both self- and conspecific-superparasitism will be an adaptive strategy when hosts are the limiting factor.
Jeffrey A. Harvey - One of the best experts on this subject based on the ideXlab platform.
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Effect of biotic and abiotic factors on reproductive parameters of the synovigenic endoparasitoid Venturia canescens
Physiological Entomology, 2003Co-Authors: Panagiotis A. Eliopoulos, Jeffrey A. Harvey, Christos G. Athanassiou, George J. StathasAbstract:Abstract. The main effects and interactions of adult age, access to food and host deprivation, on the egg load of Venturia canescens (Gravenhorst) (Hymenoptera: Ichneumonidae), a larval parasitoid of Ephestia kuehniella (Lepidoptera: Pyralidae) and other pyralids, were studied in the laboratory. Intraspecific variation in the number of ovarioles was also studied. There was a positive and significant correlation between wasp size and both egg load and ovariole number, with the reproductive system of large wasps containing significantly more ovarioles and mature eggs than small wasps. Newly emerged adult wasps contained 27 ± 2.4 ovulated (mature) eggs in their lateral oviducts. Access to food and host deprivation were the only conditions under which egg load increased with parasitoid age. Wasps that had access to hosts immediately after emergence showed a significant decline in their egg complement, irrespective of food presence. Under conditions of both host and food deprivation, there was practically no alteration of egg load with parasitoid age. A three-way analysis of variance revealed that egg load varies significantly with food or host access but not with parasitoid age. All interactions among the three factors were significant. It is confirmed that there is no egg resorption in V. canescens and that egg production stops in the absence of food.
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Lifetime Reproductive Success in the Solitary Endoparasitoid, Venturia canescens
Journal of Insect Behavior, 2001Co-Authors: Jeffrey A. Harvey, Ian F. Harvey, David J. ThompsonAbstract:Parasitoid wasps have long been considered excellent organisms in studies examining the evolution of reproductive and life-history strategies. In examining the lifetime reproductive success of parasitoids in the laboratory, most investigations have provided the insects with excess hosts and food, where they exist in a relatively constraint-free environment. Importantly, these conditions may not accurately reflect the true heterogeneity of natural systems, where suitable hosts and food sources are likely to be limiting. This study examines the influence of differences in host and food availability on reproductive and life-history parameters in an asexual strain of the solitary endoparasitoid, Venturia canescens (Hymenoptera: Ichneumonidae). Lifetime reproductive success in V. canescens was measured in response to temporal variations in host and food (honey solution) access. Cohorts of parasitoids were provided with 200 fifth-instar larvae of the Indian meal moth, Plodia interpunctella (Lepidoptera: Pyralidae), and food for variable periods daily after eclosion. V. canescens is synovigenic, and host-deprived wasps continued to mature eggs over the first few days after eclosion until the egg storage capacity was reached in the oviducts. When these wasps were subsequently provided with hosts, oogenesis resumed and continued until later in adult life. Constantly fed wasps lived longer and produced more progeny than wasps from cohorts which were alternately fed and starved or were starved from eclosion. Moreover, wasps with constant host and food access produced most progeny early in life and usually experienced prolonged periods of postreproductive survival. In contrast, the reproductive period of wasps with limited host access was more evenly distributed throughout the adult life. Consequently, the cumulative progeny production by V. canescens with constant food access was fairly uniform irrespective of host availability. Longevity and fecundity in V. canescens were positively correlated with adult size. However, variable host access had little effect on the longevity of wasps which were constantly supplied with honey. Over the first 2 days of adult life, variation in food access also had no effect on progeny production by V. canescens . We argue that manipulating temporal host and food access to parasitoids in the laboratory more closely approximates natural conditions, where these resources are likely to be spatially separated. Moreover, our findings suggest that many highly synovigenic parasitoids like V. canescens, which produce microtype (=hydropic) eggs, have a considerably higher reproductive potential than ovary dissections have revealed. Our findings are discussed in relation to life-history evolution in the parasitic Hymenoptera.
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Parasitism of baculovirus-infected Plodia interpunctella by Venturia canescens and subsequent virus transmission
Functional Ecology, 1996Co-Authors: Steven M. Sait, Michael Begon, David J. Thompson, Jeffrey A. HarveyAbstract:1. When parasitoids and pathogens compete for the same host there are often severe costs to the parasitoid. Wasps might be expected, then, to avoid parasitizing pathogen-infected hosts. 2. When the solitary endoparasitoid Venturia canescens was presented with healthy and granulosis virus-infected larvae of the Indian Meal Moth Plodia interpunctella, it did not exhibit any difference in contact or probing behaviour between healthy and infected hosts. 3. However, oviposition behaviour was influenced by the level of infection, with a significant reduction in the number of eggs laid in heavily infected hosts. 4. Transmission of the pathogen did not occur directly through oviposition. However, transmission through contamination of the environment by the parasitoid following oviposition in infected hosts was demonstrated.
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Reciprocal influences and costs of parasitism on the development of Corcyra cephalonica and its endoparasitoid Venturia canescens
Entomologia Experimentalis et Applicata, 1996Co-Authors: Jeffrey A. Harvey, David J. Thompson, Thomas J. HeyesAbstract:Many endoparasitoids develop successfully within a range of host instars. Parasitoid survival is highest when parasitism is initiated in earlier host instars, due to age-related changes in internal (physiological) host defences. Most studies examining fitness-related costs associated with differences in host instar have concentrated on the parasitoid, ignoring the effects of parasitism on the development of surviving hosts that have encapsulated parasitoid eggs. A laboratory experiment was undertaken examining fitness-related costs associated with encapsulation of Venturia canescens (Hymenoptera: Ichneumonidae) eggs by fifth (L5) instar larvae of Corcyra cephalonica (Lepidoptera: Pyralidae). Growth and development of both host and parasitoid were monitored in C. cephalonica larvae containing 0, 1, 2, or 4 parasitoid eggs. Adult size and fecundity of C. cephalonica did not vary with the number of eggs per host. However, there was a distinct increase in host mortality with egg number, although most parasitoids emerged from hosts containing a single egg. The most dramatic effect on the host was a highly significant increase in development time from parasitism to adult eclosion, with hosts containing 4 parasitoid eggs taking over 2.5 days longer to complete development than unparasitized larvae. The egg-to-adult development time and size of adult V. canescens did not vary with egg number per host, as demonstrated in a previous experiment using a different host ( Plodia interpunctella ). The results described here show that there are fitness-related costs to the host associated with resistance to parasitism.
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Venturia canescens parasitizing Galleria mellonella and Anagasta kuehniella: is the parasitoid a conformer or regulator?
Journal of Insect Physiology, 1996Co-Authors: Jeffrey A. HarveyAbstract:Abstract The effects of parasitism by Venturia canescens (Hymenoptera: Ichneumonidae) on the growth of Galleria mellonella and Anagasta kuehniella (Lepidoptera: Pyralidae) were examined by measuring the weight gain of hosts parasitized from the late second (LL2) to the fifth (L5) instar. Unparasitized G. mellonella are much larger than A. kuehniella in all corresponding stages of larval development. The development of V. canescens was more successful in A. kuehniella than G. mellonella, because late final instar parasitoids were usually unable to egress from the cuticle of G. mellonella. Parasitized G. mellonella larvae (a) show a marked reduction in weight gain, which was more apparent the earlier that parasitism occurred, and (b) left their feeding chambers to spin precocious cocoons just prior to being destroyed by the parasitoid. Weight reduction was also shown by parasitized L2–L4 A. kuehniella compared with controls, although the relationship between host size at parasitism and subsequent weight reduction was not as clear as in G. mellonella. V. canescens was therefore partially able to control host weight gain, which varied between host species, and this control was probably mediated by the parasitoid larva. Although parasitized hosts continued to grow after parasitism, V. canescens clearly arrested the development of the larger host species, G. mellonella at an earlier stage than the smaller host species, A. kuehniella. The results suggest that V. canescens, and perhaps other so-called ‘conformer’ koinobiont endoparasitoids, that exhibit flexible larval growth patterns, may also regulate host growth in response to their own nutritional and physiological requirements.
Annette Reineke - One of the best experts on this subject based on the ideXlab platform.
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gene expression changes in ephestia kuehniella caterpillars after parasitization by the endoparasitic wasp Venturia canescens analyzed through cdna aflps
Journal of Insect Physiology, 2005Co-Authors: Annette Reineke, Sandra LobmannAbstract:To understand the transcriptional response of Ephestia kuehniella caterpillars to parasitization by the endoparasitic wasp Venturia canescens, we examined patterns of gene expression in parasitized and unparasitized host caterpillars using the cDNA-AFLP (cDNA-amplified fragment length polymorphism) technique. Among the approximately 1860 cDNA-fragments detected by using 88 different AFLP primer combinations, we identified 13 transcripts in parasitized caterpillars that showed a suppressed expression pattern with cDNA-AFLP results being confirmed by virtual Northern blot or RT-PCR analysis. Apparently, two different wasp genotypes (RP, RM) seem to differ in their ability to regulate host physiology with regard to suppression of certain genes. Sequence analysis of the cDNA fragments revealed that some of the respective genes are likely to be involved in energy metabolism, protein synthesis, or in signal transduction. In addition, one sequence corresponds to a gene encoding the lepidopteran silk protein fibroin. The putative function of these genes in the interactions between endoparasitoids and their host insects is discussed.
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Presence of a novel small RNA-containing virus in a laboratory culture of the endoparasitic wasp Venturia canescens (Hymenoptera: Ichneumonidae).
Journal of insect physiology, 2005Co-Authors: Annette Reineke, Sassan AsgariAbstract:Parasitoid wasps use a variety of mechanisms to alter their host's physiology to the benefit of the developing endoparasite inside the host larva. Association of certain wasps with viruses and virus-like particles (VLPs) that contribute to their success in parasitism is one of the fascinating evolutionary adaptations conferring active or passive protection for the endoparasite from the host immune system. Venturia canescens has been shown to produce VLPs that provide protection for the developing parasitoid egg inside the host, Ephestia kuehniella. Here, we report on the presence of a novel small RNA-containing virus from V. canescens, designated as VcSRV, occurring in the ovaries of the wasp. The virus particles are found together with VcVLPs in the lumen of the calyx region of the ovaries and are injected together with the egg and VcVLPs into E. kuehniella larvae where they enter hemocytes. Alignment of the RNA-dependent RNA polymerase gene of VcSRV indicates that the virus most likely belongs to the recently described genus Iflavirus.
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Identification and expression of a small heat shock protein in two lines of the endoparasitic wasp Venturia canescens.
Comparative biochemistry and physiology. Part A Molecular & integrative physiology, 2005Co-Authors: Annette ReinekeAbstract:Increased expression of small heat shock proteins (sHSPs) is known to be a key regulatory mechanism in extending tolerance to a variety of environmental stresses. In the present study, a full-length cDNA clone encoding a member of the α-crystallin/sHSP family was isolated and characterized from the endoparasitic wasp Venturia canescens (Hymenoptera: Ichneumonidae). Western blot analysis indicated that the mature protein has a mass of about 35 kDa (Vc_sHSP35). Sequence analysis of RT-PCR products revealed that two transcript forms of the gene are expressed in different developmental stages and tissues of the wasp, with the longer form likely to contain an unspliced intron sequence. Furthermore, gene expression was analysed in ovaries of V. canescens wasps from two genetically different lines after exposure to different temperatures (heat or cold shock and heat or cold acclimation, respectively). Wasps from both lines principally showed the same cold induced change in expression of the shorter transcript form (Vc_sHSP35-2). However, expression levels were higher in wasps from one line compared to the other. These results are discussed in relation to the environmental stress resistance and molecular ecology of both V. canescens lines.
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Two coexisting lines of the endoparasitoid Venturia canescens show differences in reproductive success under conspecific superparasitism
Journal of Insect Physiology, 2003Co-Authors: Annette Reineke, Harry L.s. Roberts, Otto SchmidtAbstract:In a laboratory colony of the endoparasitic wasp Venturia canescens Grav. (Hymenoptera: Ichneumonidae), two genetically distinct lines (RP, RM) appear to coexist sympatrically. The two lines display pronounced differences in ovarian morphology, parasitism behaviour and number of offspring produced under competing superparasitism. Since V. canescens is a solitary endoparasitoid, larvae inside superparasitised hosts must compete for host possession. We examined the outcome of conspecific superparasitism between the wasp lines with different time intervals between ovipositions. The results showed that the competitive abilities of the two lines were not symmetrical. Further, the RM-line won a significantly higher fraction (around 60%) of the overall contests. Dissection of parasitoid larvae from their hosts indicated that most contests between competing larvae had occurred within the first 24 h of the eggs hatching, suggesting the advantage of the RM-line relates to physical combat. It was previously thought that the coexistence of the two lines was exclusively due to maternal effects. The results of this study indicate for the first time that these differences are based on phenotypic variations in both the larval offspring and the mother.
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Differential gene expression in two strains of the endoparasitic wasp Venturia canescens identified by cDNA-amplified fragment length polymorphism analysis
Molecular ecology, 2003Co-Authors: Annette Reineke, Otto Schmidt, Claus P. W. ZebitzAbstract:In the endoparasitic wasp Venturia canescens (Hymenoptera: Ichneumonidae) two genetically distinct lines, which differ at the VLP1 gene locus, appear to coexist sympatrically in thelytokous as well as arrhenotokous field and laboratory strains. Both lines display quite distinct morphological, physiological and behavioural variations, such as different oviposition strategies, egg numbers and growth rates during early embryonic development. To examine whether more than one gene is affected in the two lines, we applied cDNA-amplified fragment length polymorphism analysis to examine patterns of gene expression in ovaries of both wasp lines. We show that a number of ovarian transcripts have an altered expression pattern in either line, which was further confirmed by virtual Northern blot analysis. Sequence analysis of the cDNA-amplified fragment length polymorphism fragments revealed that some of the respective genes are expected to be involved in regulation of protein degradation during stress responses and in signal perception/transduction. The full-length sequence of two transcription factors (a homeodomain containing protein and a zinc finger protein) differentially expressed in both lines was obtained by RACE-polymerase chain reaction and their putative role in regulating key developmental processes during embryogenesis is discussed.
Cem Özkan - One of the best experts on this subject based on the ideXlab platform.
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Side-effects of some botanical insecticides and extracts on the parasitoid, Venturia canescens (Grav.) (Hymenoptera: Ichneumonidae) 1 Bazi bitkisel insektisitlerin ve ekstraktlarin Venturia canescens (Grav.) (Hymenoptera: Ichneumonidae) üzerindeki ya
2012Co-Authors: Hilal Tunca, Cem ÖzkanAbstract:Summary Effects of botanical insecticides, azadirachtin and pyrethrum, on the development and behavior; capsaicin and d-Limonene, on behavior of Venturia canescens Gravenhorst were determined with a two-choice test using Y-tube olfactometer. The LC50 and LC25 values for azadirachtin and pyrethrum were also determined in the third and fifth larval stages of the host Ephestia kuehniella Zeller. The third and fifth larval stages of E. kuehniella were parasitized and then these larvae were treated with LC50 and LC25 values for the same botanical insecticides. While development time of the parasitoid was prolonged, the longevity and emergence rate were reduced at the LC50 and LC25 values of azadirachtin. Pyrethrum was much more toxic for the parasitoid with LC50 value caused 100% mortality of V. canescens. LC25 value of pyrethrum caused a great reduction in parasitoid progeny, prolonged development and reduced the longevity. In addition, botanical insecticides and extracts were repellent to parasitoid adults. The use of azadirachtin, pyrethrum, capsaicin and d-Limonene is therefore not compatible with parasitoid V. canescens.
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Effect of food, light and host instar on the egg load of the synovigenic endoparasitoid Venturia canescens (Hymenoptera: Ichneumonidae)
Journal of Pest Science, 2007Co-Authors: Cem ÖzkanAbstract:Laboratory experiments investigated the effect of host instar, light and food on the number of mature eggs in ovaries (egg load) of the synovigenic parasitoid Venturia canescens (Grav.) (Hymenoptera: Ichneumonidae). The wasps that developed from third or fifth instar larvae of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) were exposed to food (honey) or had no food, had access to water or not, and were reared at the photoperiod 16:8 h light:dark or in continuous darkness at 25 ± 1°C, and 60–70% relative humidity. After death, the parasitoids were dissected to remove the reproductive systems, and mature eggs in ovaries were counted. A three-way ANOVA for egg number with host instar, food and light as factors revealed that egg load varied significantly. In addition, some interactions among the three factors were also found to be significant. The maximum average number (215.80 ± 8.51) of mature eggs was found when the parasitoids developed from third instar larvae, were exposed to continuous darkness and fed with honey. In conclusion, host instar, food supplement and photoperiod could have potential for improving biological control efficacy in stores. However, further studies determining the effect of these factors on egg laying behavior and fecundity should be done.
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Effect of food, light and host instar on the egg load of the synovigenic endoparasitoid Venturia canescens (Hymenoptera: Ichneumonidae)
Journal of Pest Science, 2007Co-Authors: Cem ÖzkanAbstract:Laboratory experiments investigated the effect of host instar, light and food on the number of mature eggs in ovaries (egg load) of the synovigenic parasitoid Venturia canescens (Grav.) (Hymenoptera: Ichneumonidae). The wasps that developed from third or fifth instar larvae of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) were exposed to food (honey) or had no food, had access to water or not, and were reared at the photoperiod 16:8 h light:dark or in continuous darkness at 25 ± 1°C, and 60–70% relative humidity. After death, the parasitoids were dissected to remove the reproductive systems, and mature eggs in ovaries were counted. A three-way ANOVA for egg number with host instar, food and light as factors revealed that egg load varied significantly. In addition, some interactions among the three factors were also found to be significant. The maximum average number (215.80 ± 8.51) of mature eggs was found when the parasitoids developed from third instar larvae, were exposed to continuous darkness and fed with honey. In conclusion, host instar, food supplement and photoperiod could have potential for improving biological control efficacy in stores. However, further studies determining the effect of these factors on egg laying behavior and fecundity should be done.
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Effect of Light on the Longevity and Fecundity of Venturia canescens (Gravenhorst) (Hymenoptera: Ichneumonidae)
2007Co-Authors: Ali Kursat Sahin, Cem Özkan, Canakkale OnsekizAbstract:The effect of light on the longevity and fecundity of Venturia canescens (Gravenhorst) (Hymenoptera: Ichneumonidae) was investigated at 25±1°C temperature and 60-70 % relative humidity. In the experiment, V. canescens was reared in L0:D24 (continuous darkness) and L16:D8 (2000 and 5000 lux light intensities), and the longevity and fecundity of the parasitoid were defined at these conditions. The results indicated that photoperiod and light intensity significantly affected the longevity and fecundity of the parasitoid. The maximum average longevity was found to be 583.92±43.46 hours in continuous darkness. The average longevity of the parasitoid decreased in L16:D8 (15.17% and 25.35% in 2000 and 5000 lux light intensities, respectively). Similarly, the maximum average fecundity was found as 193.02±4.45 in L0:D24 and average fecundity of the parasitoid decreased in L16:D8 (10.53% and 30.78% in 2000 and 5000 lux light intensity treatments, respectively). The findings of this investigation confirm that photoperiod and light intensity could have potential for improving biological control efficacy of V. canescens in grain storage warehouses.
Emmanuel Desouhant - One of the best experts on this subject based on the ideXlab platform.
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Diploid male production correlates with genetic diversity in the parasitoid wasp Venturia canescens : a genetic approach with new microsatellite markers
Ecology and Evolution, 2016Co-Authors: Marie Collet, Emmanuel Desouhant, Chloé Vayssade, Alexandra Auguste, Laurence Mouton, Thibaut Malausa, Xavier FauvergueAbstract:Sex determination is ruled by haplodiploidy in Hymenoptera, with haploid males arising from unfertilized eggs and diploid females from fertilized eggs. However, diploid males with null fitness are produced under complementary sex determination (CSD), when individuals are homozygous for this locus. Diploid males are expected to be more frequent in genetically eroded populations (such as islands and captive populations), as genetic diversity at the csd locus should be low. However, only a few studies have focused on the relation between population size, genetic diversity, and the proportion of diploid males in the field. Here, we developed new microsatellite markers in order to assess and compare genetic diversity and diploid male proportion (DMP) in populations from three distinct habitat types-mainland, island, or captive-, in the parasitoid wasp Venturia canescens. Eroded genetic diversity and higher DMP were found in island and captive populations, and habitat type had large effect on genetic diversity. Therefore, DMP reflects the decreasing genetic diversity in small and isolated populations. Thus, Hymenopteran populations can be at high extinction risk due to habitat destruction or fragmentation.
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Diploid male production correlates with genetic diversity in the parasitoid wasp Venturia canescens: a genetic approach with new microsatellite markers
2016Co-Authors: Marie Collet, Emmanuel Desouhant, Chloé Vayssade, Alexandra Auguste, Laurence Mouton, Thibaut Malausa, Xavier FauvergueAbstract:Sex determination is ruled by haplodiploidy in Hymenoptera, with haploid males arising from unfertilized eggs and diploid females from fertilized eggs. However, diploid males with null fitness are produced under Complementary Sex Determination (CSD), when individuals are homozygous for this locus. Diploid males are expected to be more frequent in genetically eroded populations (such as islands and captive populations), as genetic diversity at the csd locus should be low. However, only a few studies have focused on the relation between population size, genetic diversity and the proportion of diploid males in the field. Here, we developed new microsatellites markers in order to assess and compare genetic diversity and diploid male proportion in populations from three distinct habitat types (mainland, island or captive), in the parasitoid wasp Venturia canescens. Eroded genetic diversity and higher diploid male proportion were found in island and captive populations, and habitat type had large effect on genetic diversity. Therefore, diploid male proportion reflects the decreasing genetic diversity in small and isolated populations. Thus, Hymenopteran populations can be at high extinction risk due to habitat destruction or fragmentation.
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occurrence of arrhenotoky and thelytoky in a parasitic wasp Venturia canescens hymenoptera ichneumonidae effect of endosymbionts or existence of two distinct reproductive modes
European Journal of Entomology, 2013Co-Authors: Vincent Foray, Hélène Henri, Patricia Gibert, Sonia Martínez, Emmanuel DesouhantAbstract:Endosymbiotic organisms are known to manipulate the reproductive biology of their hosts. Incomplete prevalence of endosymbiont inducing thelytokous parthenogenesis results in the coexistence of sexual and asexual individuals, and could account for the maintenance of sexual reproduction in certain populations or species. In the parasitoid Venturia canescens, arrhenotokous ("sexual") and thelytokous ("asexual") individuals occur sympatrically. We aimed to determine whether endosymbionts are implicated in the thelytoky of V. canescens. After screening females of the two reproductive modes for several reproductive parasites: bacteria (Wolbachia, Rickettsia, Bacteroidetes, Spiroplasma, Arsenophonus) and Microsporidia, we concluded that thelytoky in V. canescens is not induced by any of these parasites and confirmed its suitability as a biological model for solving the evolutionary enigma of the maintenance of sexual reproduction.
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Differential thermal performance curves in response to different habitats in the parasitoid Venturia canescens
Naturwissenschaften, 2011Co-Authors: Vincent Foray, Patricia Gibert, Emmanuel DesouhantAbstract:Environmental variability is expected to be important in shaping performance curves, reaction norms of phenotypic traits related to fitness. Models predict that the breadth of performance curves should increase with environmental variability at the expense of maximal performance. In this study, we compared the thermal performance curves of two sympatric populations of the parasitoid Venturia canescens that were observed under contrasting thermal regimes in their respective preferred habitats and differing in their modes of reproduction. Our results confirm the large effect of developmental temperature on phenotypic traits of insects and demonstrate that thelytokous and arrhenotokous wasps respond differently to temperature during development, in agreement with model predictions. For traits related to fecundity, thelytokous parasitoids, which usually occur in stable thermal conditions, exhibit specialist performance curves, maximising their reproductive success under a restricted range of temperature. In contrast, arrhenotokous parasitoids, which occur in variable climates, exhibit generalist performance curves, in keeping with the hypothesis "jack of all temperatures, master of none".
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The dynamics of energyallocation in adult arrhenotokous and thelytokous Venturia canescens
2010Co-Authors: Perrine Pelosse, Carlos Bernstein, Isabelle Amat, Emmanuel DesouhantAbstract:The ability to adjust resource allocation to the quality of the environment has broad implications for animal reproductive success. Organisms with complex life cycles that may experience various selection pressures during their lifetimeareexpectedtoevolve mechanisms to modulate theresource allocation strategies adopted during ontogeny to the conditions encountered by the adult. In the parasitoid Venturia canescens Gravenhorst (Hymenoptera: Ichneumonidae), thelytoky appears to have been selected for in anthropogenic habitats, where hosts are relatively numerous and food is absent, and arrhenotoky in natural habitats where hosts are more scarce and food is present. A previousstudypostulated that duringtheirjuvenilestage,females ofbothreproductivemodes adoptstrategies of energy allocation in accordance with these conditions, possibly providing a direct short-term advantage to arrhenotokous forms, which partially co-occur with thelytokous forms under natural conditions. To test this assumption, we provided daily adult thelytokous and arrhenotokous females witha smallnumberofhoststogetherwithfood.Tocomparetheirlifetimeresourceallocationstrategies, we recorded wasp longevities, egg loads, and carbohydrate reserves in wasps of different ages. Our analysis indicates that thelytokous females are able, to a certain extent, to cope with these conditions, because they reached the same longevity as arrhenotokous females. Nevertheless, thelytokous females suffered from a higher degree of time limitation compared with arrhenotokous ones, and arrhenotokous wasps appeared to maintain their energetic advantage over the adult stage. These results provide new insights, and point to the consideration of other activities, such as flight performance and ⁄or ability to reach food and hosts, in the understanding of the role of resource allocation strategies inthe maintenanceofsex inthisspecies.
