The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform
Susan L Swarbrick - One of the best experts on this subject based on the ideXlab platform.
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host suppression and stability in a parasitoid host system experimental demonstration
Science, 2005Co-Authors: William W Murdoch, Cheryl J Briggs, Susan L SwarbrickAbstract:We elucidate the mechanisms causing stability and severe resource suppression in a consumer-resource system. The consumer, the parasitoid Aphytis, rapidly controlled an experimentally induced outbreak of the resource, California red scale, an agricultural pest, and imposed a low, stable pest equilibrium. The results are well predicted by a mechanistic, independently parameterized model. The key mechanisms are widespread in nature: an invulnerable adult stage in the resource population and rapid consumer development. Stability in this biologically nondiverse agricultural system is a property of the local interaction between these two species, not of spatial processes or of the larger ecological community.
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parasitoid coexistence linking spatial field patterns with mechanism
Ecology, 2004Co-Authors: Elizabeth T Borer, William W Murdoch, Susan L SwarbrickAbstract:Coexistence of resource specialists can be maintained through various spatial mechanisms, each potentially inducing different resource dynamics. We used observational data to suggest plausible spatial coexistence mechanisms for Aphytis melinus and Encarsia perniciosi, two parasitoids of California red scale. Aphytis consistently produced more progeny from scale insects on leaves, and Encarsia produced progeny equally from scale insects on leaves and stems. To investigate the mechanism inducing this pattern, we performed field experiments to test two possible explanations. In the absence of substrate choice and at a given abundance of scale, the number of progeny produced by each species was the same on stems as on leaves. When given a choice, Encarsia had no substrate preference, while Aphytis preferred scale insects on leaves, producing results qualitatively similar to the field observations. Ecological theory suggests that this form of habitat preference may facilitate coexistence. Although this mechanism of coexistence is clearly compatible with biological control by multiple natural enemies in the red scale system, theory dealing with this type of interaction has not thoroughly examined the predictions for resource dynamics.
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testing intraguild predation theory in a field system does numerical dominance shift along a gradient of productivity
Ecology Letters, 2003Co-Authors: Elizabeth T Borer, William W Murdoch, Cheryl J Briggs, Susan L SwarbrickAbstract:Although ecological theory exists to predict dynamics in communities with intraguild predation (IGP), few empirical tests have examined this theory. IGP theory, in particular, predicts that when two competitors interact via IGP, with increasing resource productivity: (1) the IG predator will increase in abundance as the IG prey declines, and (2) increasing dominance of the IG predator will cause resource density to increase. Here, we provide a first test of these predictions in a field community consisting of a scale insect and its two specialist parasitoids, Aphytis melinus (the IG predator) and Encarsia perniciosi (the IG prey). The shared resource, California red scale, is a pest of citrus, and its productivity varies across a threefold range among citrus cultivars. We examined both absolute and relative densities of parasitoids along this natural gradient of scale productivity in three citrus cultivars (orange, grapefruit and lemon). Although both parasitoid species were found in all three cultivars, their abundances reflected those predicted by IGP theory: the IG prey species dominated at low productivity and the IG predator dominated at high productivity. This relationship was caused by an increase in Aphytis density with productivity. In addition, the density of scale increased with the dominance of the IG predator. These results from a field system demonstrate the important dynamic outcomes for food webs with IGP.
D Rosen - One of the best experts on this subject based on the ideXlab platform.
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phylogenetic analysis of parthenogenesis inducing wolbachia in the genus Aphytis hymenoptera aphelinidae
Insect Molecular Biology, 1998Co-Authors: Yuval Gottlieb, Einat Zchorifein, O Faktor, D RosenAbstract:Parthenogenesis-inducing intracellular bacteria of the genus Wolbachia are found in a variety of parasitoid wasp genera. The presence of Wolbachia in the uniparental Aphytis species A. fingnanensis Compere, A. diaspidis (Howard), A. chilensis Howard, and A. chrysomphali (Mercet) was tested using primers specific for the ftsZ gene. The symbiont was detected in all of these species. Wolbachia ftsZ genes that were sequenced from the four hosts show a high degree of similarity. Both the PCR with specific primers for group ‘A’ and phylogenetic analysis place these Wolbachia in group ‘A’. The fact that the tested Aphytis species belong to different phylogenetic groups and harbour what seem to be almost identical Wolbachia, lends credence to the horizontal transmission hypothesis.
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parthenogenesis inducing microorganisms in Aphytis hymenoptera aphelinidae
Insect Molecular Biology, 1995Co-Authors: Einat Zchorifein, O Faktor, M Zeidan, Yuval Gottlieb, Henryk Czosnek, D RosenAbstract:Production of males in uniparental lines of two species in the parasitic wasp genus Aphytis was induced by rifampicin, and male sexual functioning was determined. Wolbachia-specific 16S rDNA primers were used in a PCR in order to: (1) assess correlation between thelytokous reproduction and the presence of Wolbachia; (2) detect the loss of Wolbachia DNA in uniparental A. lingnanensis following antibiotic treatments, with or without the presence of a host; and (3) clone and sequence part of the Wolbachia 16S rDNA from the uniparental Aphytis species for phylogenetic studies. Males produced viable sperm that was transferred to the female spermatheca following mating. However, sperm failure to effect egg fertilization resulted in all-male progeny. Wolbachia were found in the two uniparental (A. lingnanensis and A. diaspidis) but not in the two biparental (A. lingnanensis and A. melinus) Aphytis lines tested. They can be detected in wasps up to 7 days following antibiotic treatments, regardless of the presence of host. The 16S rDNA for the symbionts in the two Aphytis species is virtually identical, and is most closely related to the Wolbachia found in Muscidifurax uniraptor (Pteromalidae).
George E. Heimpel - One of the best experts on this subject based on the ideXlab platform.
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Hyperparasitism by ablerus clisiocampae ashmead (Hymenoptera: Aphelinidae)
1999Co-Authors: David Kattari, George E. Heimpel, Paul J. Ode, Jay A RosenheimAbstract:Ablerus clisiocampae (Hymenoptera: Aphelinidae) is known as a parasitoid both of diaspidid scale insects and lepidopteran eggs. Although it has been suspected that A. clisiocampae is a secondary (hyper) parasitoid of diaspidid scale insects, direct evidence of hyperparasitism has been lacking. We used observation and rearing data from field- collected material to demonstrate hyperparasitism of three species of diaspidid scale in- sects, and primary parasitism of two species of parasitoid wasps by A. clisiocampae. Ablerus clisiocampae was found feeding on Aphytis aonidiae (Hymenoptera: Aphelinidae) attacking San Jose scale {Quadraspidiotiis perniciosus) and Comperiella bifasciata (Hy- menoptera: Encyrtidae) attacking California red scale {Aonidiella aurantii) and yellow scale (A. citrina). Ablerus clisiocampae were associated with pupal Aphytis aonidiae and pupal and pharate adult C. bifasciata. All Ablerus clisiocampae reared for this study were females.
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effects of time limitation and egg limitation on lifetime reproductive success of a parasitoid in the field
The American Naturalist, 1998Co-Authors: George E. Heimpel, Marc Mangel, Jay A RosenheimAbstract:Abstract We used field observations of freely foraging Aphytis aonidiae parasitoids in conjunction with results of laboratory studies of A. aonidiae and other Aphytis species to simulate lifetime patterns of behavior and reproduction. Field observations provided estimates of encounter rates with three classes of hosts, the mortality rate from predation on adult parasitoids, and host‐handling times for oviposition and host feeding by adult wasps. A series of physiological parameters, including the egg maturation rate and the value of host‐feeding meals, were estimated from previously published studies. Plasticity in parasitoid behavior was incorporated in two ways. For one set of simulations we used a behavioral rule derived empirically from observations of parasitoids made in the field, and for another we used a dynamic state‐variable model to generate a set of behavioral rules that maximize lifetime reproductive success. As was expected, the empirically derived rule led to better matches with field obser...
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Adult feeding and lifetime reproductive success in the parasitoid Aphytis melinus
Entomologia Experimentalis et Applicata, 1997Co-Authors: George E. Heimpel, Jay A Rosenheim, David KattariAbstract:The diet of adult females of the parasitoid Aphytis melinus DeBach (Hymenoptera: Aphelinidae) includes host insects and sugar-rich foods such as nectar and honeydew. We compared the contributions of host feeding to longevity and fecundity in A. melinus females in the presence and in the absence of honey meals. First, we assessed the longevity of females that were not allowed to oviposit. While the longevity of females fed honey was significantly increased by host feeding (median ages were 30.5 days for host-fed females and 17 days for females not allowed to host feed), the lifespan of parasitoids not fed honey did not exceed 3 days for any individual and there was no effect of host feeding on longevity in this group. In the second set of experiments, we assessed the fecundity and longevity of females allowed to oviposit. We conducted two experiments, one in which honey was continuously available, and one in which honey was not available. In both experiments, daily observations were made of females that were either allowed to host feed or manually prevented from host feeding. In the presence of honey, host feeding significantly increased both fecundity and longevity, and in the absence of honey, parasitoids died within 2 days and host feeding had no significant effect on either fecundity or longevity. The lifetime fecundity of females fed honey but not hosts exceeded the initial egg complement by 60% on average. Approximately one host per day was used for host feeding whether honey was supplied or not, and each host-feeding meal contributed approximately 3.9 eggs to the lifetime fecundity of honey-fed females. In the last experiment, we compared the rate of egg resorption over a 36-h period in A. melinus females that were deprived of hosts and either fed honey or starved. While no egg resorption was detected in honey-fed females over this time period, starved females resorbed approximately 9 eggs. Thus, the availability of a sugar-rich food interacts strongly with host feeding in influencing longevity and fecundity and has a strong direct effect on egg resorption.
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predation on adult Aphytis parasitoids in the field
Oecologia, 1997Co-Authors: George E. Heimpel, Jay A Rosenheim, Marc MangelAbstract:We report on predation on adult females of the parasitoids Aphytis aonidiae and A. vandenboschi (Hymenoptera: Aphelinidae) foraging in the field. During 89.6 h of observation, we witnessed 18 encounters with predators, 6 of which resulted in parasitoid capture. Three classes of generalist predators attacked Aphytis: spiders (unidentified Salticidae and Thomisidae), workers of the Argentine ant, Linepithema humile, and nymphs of the assassin bug Zelus renardii (Hemiptera: Reduviidae). Although observations were conducted during most months of the year, encounters with predators occurred only during September, October and November. During these months, encounters with predators occurred on average every 3.2 h of observation, with one in three encounters resulting in parasitoid capture. Peaks in predation coincided with population peaks of A. aonidiae, but were unrelated to population dynamics of any of the predators. We compare these results with previously published laboratory studies on longevity of Aphytis parasitoids, and conclude that predation pressure has the potential to severely limit parasitoid fitness in the field.
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egg limitation host quality and dynamic behavior by a parasitoid in the field
Ecology, 1996Co-Authors: George E. Heimpel, Jay A Rosenheim, Marc MangelAbstract:Patterns of host selection and host use by insects with parasitic lifestyles are predicted to be fundamentally dynamic, responding to environmental conditions and physi- ological states. A particularly robust prediction is that the number of mature eggs that a female carries (her "egg load") should influence behavior. As egg load decreases, females are predicted to exhibit increasingly selective host use patterns. We tested the hypothesis that egg load and host size influence the behavior of the parasitoid wasp Aphytis aonidiae attacking the armored scale insect Quadraspidiotus perniciosus. Aphytis females can use hosts either for oviposition or for adult "host feeding," which is the consumption of host material by adult parasitoids. Theory predicts that host feeding should be (i) favored by low egg loads and (ii) more prevalent on lower-quality (smaller) hosts. We conducted observations of in- dividual females foraging freely in the field to determine whether hosts were used for ovi- position or for host feeding. As predicted by theory, the likelihood that a host was used for oviposition (as opposed to host feeding) increased with both parasitoid egg load and host size. Thus, parasitoids exhibited higher host-selectivity at lower egg loads. Since egg load and a parasitoid's experience with hosts were not experimentally separated, the egg load effect could in principle have been either direct or indirect and operating through a correlation with experience. In either case, this result constitutes the first demonstration of a link between physiological state and oviposition behavior by a parasitoid in the field. Parasitoid age, as measured using a wing wear index, did not influence behavior. A laboratory study revealed that the relationship between a host's size and the size and initial egg load of the parasitoid developing on that host was positive, but that it followed a pattern of diminishing returns. No effect of host size on behavior could be detected over the range of host sizes that were within the asymptotic region of this relationship.
Einat Zchorifein - One of the best experts on this subject based on the ideXlab platform.
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phylogenetic analysis of parthenogenesis inducing wolbachia in the genus Aphytis hymenoptera aphelinidae
Insect Molecular Biology, 1998Co-Authors: Yuval Gottlieb, Einat Zchorifein, O Faktor, D RosenAbstract:Parthenogenesis-inducing intracellular bacteria of the genus Wolbachia are found in a variety of parasitoid wasp genera. The presence of Wolbachia in the uniparental Aphytis species A. fingnanensis Compere, A. diaspidis (Howard), A. chilensis Howard, and A. chrysomphali (Mercet) was tested using primers specific for the ftsZ gene. The symbiont was detected in all of these species. Wolbachia ftsZ genes that were sequenced from the four hosts show a high degree of similarity. Both the PCR with specific primers for group ‘A’ and phylogenetic analysis place these Wolbachia in group ‘A’. The fact that the tested Aphytis species belong to different phylogenetic groups and harbour what seem to be almost identical Wolbachia, lends credence to the horizontal transmission hypothesis.
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distribution of parthenogenesis inducing symbionts in ovaries and eggs of Aphytis hymenoptera aphelinidae
Current Microbiology, 1998Co-Authors: Einat Zchorifein, Richard T Roush, David RosenAbstract:In parasitic Hymenoptera, severe sex ratio distortions are sometimes associated with the presence of symbiotic microorganisms. Symbiont-induced uniparental reproduction is found in several species of the genus Aphytis and is suspected in others. These intracellular bacteria (called Wolbachia) reside within the egg cytoplasm. In order to follow their vertical transmission, the distribution pattern of the symbionts in ovaries and eggs of two uniparental lines (A. lingnanensis and A. yanonensis) was studied by electron, confocal, and two-photon microscopy. The results obtained suggest that Wolbachia move from nurse cells to developing oocytes. In freshly laid eggs, the symbionts are concentrated in the posterior pole, away from the micropyle, and in later stages of embryogenesis they are found surrounding nuclei throughout the embryo.
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parthenogenesis inducing microorganisms in Aphytis hymenoptera aphelinidae
Insect Molecular Biology, 1995Co-Authors: Einat Zchorifein, O Faktor, M Zeidan, Yuval Gottlieb, Henryk Czosnek, D RosenAbstract:Production of males in uniparental lines of two species in the parasitic wasp genus Aphytis was induced by rifampicin, and male sexual functioning was determined. Wolbachia-specific 16S rDNA primers were used in a PCR in order to: (1) assess correlation between thelytokous reproduction and the presence of Wolbachia; (2) detect the loss of Wolbachia DNA in uniparental A. lingnanensis following antibiotic treatments, with or without the presence of a host; and (3) clone and sequence part of the Wolbachia 16S rDNA from the uniparental Aphytis species for phylogenetic studies. Males produced viable sperm that was transferred to the female spermatheca following mating. However, sperm failure to effect egg fertilization resulted in all-male progeny. Wolbachia were found in the two uniparental (A. lingnanensis and A. diaspidis) but not in the two biparental (A. lingnanensis and A. melinus) Aphytis lines tested. They can be detected in wasps up to 7 days following antibiotic treatments, regardless of the presence of host. The 16S rDNA for the symbionts in the two Aphytis species is virtually identical, and is most closely related to the Wolbachia found in Muscidifurax uniraptor (Pteromalidae).
Jay A Rosenheim - One of the best experts on this subject based on the ideXlab platform.
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Hyperparasitism by ablerus clisiocampae ashmead (Hymenoptera: Aphelinidae)
1999Co-Authors: David Kattari, George E. Heimpel, Paul J. Ode, Jay A RosenheimAbstract:Ablerus clisiocampae (Hymenoptera: Aphelinidae) is known as a parasitoid both of diaspidid scale insects and lepidopteran eggs. Although it has been suspected that A. clisiocampae is a secondary (hyper) parasitoid of diaspidid scale insects, direct evidence of hyperparasitism has been lacking. We used observation and rearing data from field- collected material to demonstrate hyperparasitism of three species of diaspidid scale in- sects, and primary parasitism of two species of parasitoid wasps by A. clisiocampae. Ablerus clisiocampae was found feeding on Aphytis aonidiae (Hymenoptera: Aphelinidae) attacking San Jose scale {Quadraspidiotiis perniciosus) and Comperiella bifasciata (Hy- menoptera: Encyrtidae) attacking California red scale {Aonidiella aurantii) and yellow scale (A. citrina). Ablerus clisiocampae were associated with pupal Aphytis aonidiae and pupal and pharate adult C. bifasciata. All Ablerus clisiocampae reared for this study were females.
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effects of time limitation and egg limitation on lifetime reproductive success of a parasitoid in the field
The American Naturalist, 1998Co-Authors: George E. Heimpel, Marc Mangel, Jay A RosenheimAbstract:Abstract We used field observations of freely foraging Aphytis aonidiae parasitoids in conjunction with results of laboratory studies of A. aonidiae and other Aphytis species to simulate lifetime patterns of behavior and reproduction. Field observations provided estimates of encounter rates with three classes of hosts, the mortality rate from predation on adult parasitoids, and host‐handling times for oviposition and host feeding by adult wasps. A series of physiological parameters, including the egg maturation rate and the value of host‐feeding meals, were estimated from previously published studies. Plasticity in parasitoid behavior was incorporated in two ways. For one set of simulations we used a behavioral rule derived empirically from observations of parasitoids made in the field, and for another we used a dynamic state‐variable model to generate a set of behavioral rules that maximize lifetime reproductive success. As was expected, the empirically derived rule led to better matches with field obser...
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Adult feeding and lifetime reproductive success in the parasitoid Aphytis melinus
Entomologia Experimentalis et Applicata, 1997Co-Authors: George E. Heimpel, Jay A Rosenheim, David KattariAbstract:The diet of adult females of the parasitoid Aphytis melinus DeBach (Hymenoptera: Aphelinidae) includes host insects and sugar-rich foods such as nectar and honeydew. We compared the contributions of host feeding to longevity and fecundity in A. melinus females in the presence and in the absence of honey meals. First, we assessed the longevity of females that were not allowed to oviposit. While the longevity of females fed honey was significantly increased by host feeding (median ages were 30.5 days for host-fed females and 17 days for females not allowed to host feed), the lifespan of parasitoids not fed honey did not exceed 3 days for any individual and there was no effect of host feeding on longevity in this group. In the second set of experiments, we assessed the fecundity and longevity of females allowed to oviposit. We conducted two experiments, one in which honey was continuously available, and one in which honey was not available. In both experiments, daily observations were made of females that were either allowed to host feed or manually prevented from host feeding. In the presence of honey, host feeding significantly increased both fecundity and longevity, and in the absence of honey, parasitoids died within 2 days and host feeding had no significant effect on either fecundity or longevity. The lifetime fecundity of females fed honey but not hosts exceeded the initial egg complement by 60% on average. Approximately one host per day was used for host feeding whether honey was supplied or not, and each host-feeding meal contributed approximately 3.9 eggs to the lifetime fecundity of honey-fed females. In the last experiment, we compared the rate of egg resorption over a 36-h period in A. melinus females that were deprived of hosts and either fed honey or starved. While no egg resorption was detected in honey-fed females over this time period, starved females resorbed approximately 9 eggs. Thus, the availability of a sugar-rich food interacts strongly with host feeding in influencing longevity and fecundity and has a strong direct effect on egg resorption.
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predation on adult Aphytis parasitoids in the field
Oecologia, 1997Co-Authors: George E. Heimpel, Jay A Rosenheim, Marc MangelAbstract:We report on predation on adult females of the parasitoids Aphytis aonidiae and A. vandenboschi (Hymenoptera: Aphelinidae) foraging in the field. During 89.6 h of observation, we witnessed 18 encounters with predators, 6 of which resulted in parasitoid capture. Three classes of generalist predators attacked Aphytis: spiders (unidentified Salticidae and Thomisidae), workers of the Argentine ant, Linepithema humile, and nymphs of the assassin bug Zelus renardii (Hemiptera: Reduviidae). Although observations were conducted during most months of the year, encounters with predators occurred only during September, October and November. During these months, encounters with predators occurred on average every 3.2 h of observation, with one in three encounters resulting in parasitoid capture. Peaks in predation coincided with population peaks of A. aonidiae, but were unrelated to population dynamics of any of the predators. We compare these results with previously published laboratory studies on longevity of Aphytis parasitoids, and conclude that predation pressure has the potential to severely limit parasitoid fitness in the field.
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egg limitation host quality and dynamic behavior by a parasitoid in the field
Ecology, 1996Co-Authors: George E. Heimpel, Jay A Rosenheim, Marc MangelAbstract:Patterns of host selection and host use by insects with parasitic lifestyles are predicted to be fundamentally dynamic, responding to environmental conditions and physi- ological states. A particularly robust prediction is that the number of mature eggs that a female carries (her "egg load") should influence behavior. As egg load decreases, females are predicted to exhibit increasingly selective host use patterns. We tested the hypothesis that egg load and host size influence the behavior of the parasitoid wasp Aphytis aonidiae attacking the armored scale insect Quadraspidiotus perniciosus. Aphytis females can use hosts either for oviposition or for adult "host feeding," which is the consumption of host material by adult parasitoids. Theory predicts that host feeding should be (i) favored by low egg loads and (ii) more prevalent on lower-quality (smaller) hosts. We conducted observations of in- dividual females foraging freely in the field to determine whether hosts were used for ovi- position or for host feeding. As predicted by theory, the likelihood that a host was used for oviposition (as opposed to host feeding) increased with both parasitoid egg load and host size. Thus, parasitoids exhibited higher host-selectivity at lower egg loads. Since egg load and a parasitoid's experience with hosts were not experimentally separated, the egg load effect could in principle have been either direct or indirect and operating through a correlation with experience. In either case, this result constitutes the first demonstration of a link between physiological state and oviposition behavior by a parasitoid in the field. Parasitoid age, as measured using a wing wear index, did not influence behavior. A laboratory study revealed that the relationship between a host's size and the size and initial egg load of the parasitoid developing on that host was positive, but that it followed a pattern of diminishing returns. No effect of host size on behavior could be detected over the range of host sizes that were within the asymptotic region of this relationship.