The Experts below are selected from a list of 273 Experts worldwide ranked by ideXlab platform
Alberto Urbaneja - One of the best experts on this subject based on the ideXlab platform.
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Overstinging by hymenopteran parasitoids causes mutilation and surplus killing of hosts
Journal of Pest Science, 2018Co-Authors: Ruth Cebolla, Alberto Urbaneja, Pilar Vanaclocha, Alejandro TenaAbstract:An appraisal of the regulatory role of natural enemies on target pests requires the identification of the mechanisms/traits that enhance the ability of an organism to control the density of its prey/host. After stinging herbivore hosts with their ovipositor, hymenopteran parasitoids tend to reject them without ovipositing or host-feeding. Termed pseudoparasitism, the frequency and consequences of this type of attack (hereafter oversting) have been largely disregarded in the hymenopteran parasitoid literature. We choose the parasitoids Aphytis melinus and A. chrysomphali and their common host Aonidiella aurantii as a model system to study this behavior. Using field and laboratory observations, we showed that overstinging is a common behavior in the wild. Under controlled conditions, overstinging occurred more frequently than host-feeding, a behavioral trait that is used to evaluate the potential of parasitoids as biological control agents. Oversting reduced the fecundity and survival of the herbivore host. When we compared between parasitoid species that attack the same host species, the virulence and frequency of this behavior depended on parasitoid species. These results demonstrate that overstinging should be incorporated in the models of host–parasitoid interactions to analyze population dynamics as well as in the future selection of parasitoids for biological control.
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Negative effect of global warming on biological control is mitigated by direct competition between sympatric parasitoids
Biological Control, 2018Co-Authors: Ruth Cebolla, Alberto Urbaneja, Joan Van Baaren, Alejandro TenaAbstract:Parasitoids are among the most important and successful groups of natural enemies used in the biological control of insect pests. In most systems, several parasitoid species can parasitize the same pest. The coexistence of parasitoids in agroecosystems and their efficacy as biological control agents may be disrupted by global warming. An increase of approximately 3 degrees C is predicted by the end of the twenty-first century in the Mediterranean basin (IPCC, 2014). In this context, we compared the present and future performance of two sympatric parasitoids of the genus Aphytis (Hymenoptera Aphelinidae), which control the armoured scale Aonidiella aurantii (Hemiptera Diaspididae) in Mediterranean citrus, either alone or in combination. The net reproductive rate (R0) of the introduced Aphytis melinus DeBach was higher than that of its competitor, the native Aphytis chrysomphali (Mercer), under current conditions. The two parasitoids responded differently to higher temperature and competition. The R0 of A. chrysomphali decreased by 50% when both parasitoids competed in the same patch, but was not affected by the temperature increase. The R0 of A. melinus decreased approximately 46% with the increase in temperature because the proportion of females was reduced. However, the presence of A. chrysomphali competing in the same patch mitigated the negative effect of the increase in temperature on A. melinus (R0 decreased by only 16%). Overall, our results suggest that global warming will have a negative effect on the biological control of A. aurantii and that this effect will be higher in areas, such as southern Spain, where A. melinus has displaced A. chrysomphali.
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Does host quality dictate the outcome of interference competition between sympatric parasitoids? Effects on their coexistence
Animal Behaviour, 2017Co-Authors: Ruth Cebolla, Alberto Urbaneja, Pablo Bru, Alejandro TenaAbstract:The suitability and quality of herbivorous insect hosts for hymenopteran parasitoids is dynamic, varying with host development. Generally, within a host species, large hosts (i.e. older instars) are considered of higher quality for parasitoid development. Studies of interspecific competition between parasitoids have considered the effect of host instar on indirect competition but its effect on interference competition remains unknown. Here, we report the first results on whether the quality of host instars might dictate the outcome of interference competition between sympatric parasitoids of the genus Aphytis (Hymenoptera: Aphelinidae) when they attack low-quality (second) and high-quality (third) instars of their common host Aonidiella aurantii (Hemiptera: Diaspididae). Oviposition behaviour (host acceptance and clutch size) in low- and high-quality host instars was similar for both Aphytis species in the absence of competition. When they found heterospecific parasitized hosts of high quality, Aphytis melinus laid more eggs and accepted significantly more hosts than Aphytis chrysomphali, whereas there were no significant differences in the low-quality instar. This result suggests that interference competition is mediated by host quality. However, the progeny proportion of both parasitoids in multiparasitized hosts (outcome of competition) was independent of host quality and A. melinus always emerged at higher rates. Therefore, the result of interference competition between these sympatric parasitoids was not affected by host quality and this competition will contribute to the displacement of the native A. chrysomphali by the introduced A. melinus, which has been observed in some areas of the Mediterranean basin.
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postteneral protein feeding may improve biological control efficiency of Aphytis lingnanensis and Aphytis melinus
Journal of Insect Science, 2014Co-Authors: Pilar Vanaclocha, Maria Jesús Verdú, Dan Papacek, Alberto UrbanejaAbstract:The augmentative releases of mass-reared Aphytis spp. (Hymenoptera: Aphelinidae) parasitoids are widely used against armored scales. The nutritional status and the initial egg load of Aphytis spp. females are key to their success as biological control agents. For these reasons, this work focuses on the study of providing a protein feed to Aphytis lingnanensis (Compere) and A. melinus DeBach to improve the egg load before their release. The addition of protein to a honey diet during the first 2 d after the adult parasitoid emergence increased the initial egg load in both species of parasitoids by more than five eggs. Furthermore, the addition of protein increased the total number of eggs laid by A. lingnanensis on oleander scale, Aspidiotus nerii Bouche (Hemiptera: Diaspididae). In contrast, this effect was not observed on A. melinus probably because A. nerii is considered a suboptimal host for this parasitoid. The host-feeding activities of the two Aphytis species were differentially affected by the addition of protein to their diets. These results may have direct implications for augmentative biological control programs, especially during transportation from insectaries to the field, a period of time when parasitoids are deprived of hosts.
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Acute toxicity in laboratory tests of fresh and aged residues of pesticides used in citrus on the parasitoid Aphytis melinus
Journal of Pest Science, 2013Co-Authors: P. Vanaclocha, C. Vidal-quist, S. Oheix, Helena Montón, L. Planes, Alejandro Tena, Jordi Catalan, María J Verdú, Alberto UrbanejaAbstract:California red scale Aonidiella aurantii (Maskell) (Hemiptera: Diaspididae) is a worldwide citrus key pest. One of the control strategies currently promoted in the Mediterranean basin is the augmentative release of the parasitoid Aphytis melinus DeBach (Hymenoptera: Aphelinidae). A clear understanding of the impact that pesticides commonly used in citrus have on this parasitoid is therefore essential to assure the efficacy of the method. The aims of this study were to evaluate the lethal effects of freshly applied and laboratory-aged residues of eighteen selected pesticides recommended in IPM for citrus on A. melinus adults. According to their toxicity on A. melinus, the pesticides could be divided in four groups. Etofenprox and chlorpyrifos were harmful and persistent; abamectin was moderately harmful and slightly persistent; dimethoate, chlorpyrifos-methyl, and spirodiclofen were slightly harmful and moderately persistent; and azadirachtin, etoxazole, fenbutaestan, hexythiazox, mancozeb, petroleum oil, pirimicarb, propargite, pymetrozine, pyriproxyfen, spirotetramat, and tebufenpyrad were considered harmless. The information presented here will help us to integrate A. melinus release within an IPM for citrus in which pesticides are still used.
Alejandro Tena - One of the best experts on this subject based on the ideXlab platform.
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Negative effect of global warming on biological control is mitigated by direct competition between sympatric parasitoids
Biological Control, 2018Co-Authors: Ruth Cebolla, Alberto Urbaneja, Joan Van Baaren, Alejandro TenaAbstract:Parasitoids are among the most important and successful groups of natural enemies used in the biological control of insect pests. In most systems, several parasitoid species can parasitize the same pest. The coexistence of parasitoids in agroecosystems and their efficacy as biological control agents may be disrupted by global warming. An increase of approximately 3 degrees C is predicted by the end of the twenty-first century in the Mediterranean basin (IPCC, 2014). In this context, we compared the present and future performance of two sympatric parasitoids of the genus Aphytis (Hymenoptera Aphelinidae), which control the armoured scale Aonidiella aurantii (Hemiptera Diaspididae) in Mediterranean citrus, either alone or in combination. The net reproductive rate (R0) of the introduced Aphytis melinus DeBach was higher than that of its competitor, the native Aphytis chrysomphali (Mercer), under current conditions. The two parasitoids responded differently to higher temperature and competition. The R0 of A. chrysomphali decreased by 50% when both parasitoids competed in the same patch, but was not affected by the temperature increase. The R0 of A. melinus decreased approximately 46% with the increase in temperature because the proportion of females was reduced. However, the presence of A. chrysomphali competing in the same patch mitigated the negative effect of the increase in temperature on A. melinus (R0 decreased by only 16%). Overall, our results suggest that global warming will have a negative effect on the biological control of A. aurantii and that this effect will be higher in areas, such as southern Spain, where A. melinus has displaced A. chrysomphali.
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Overstinging by hymenopteran parasitoids causes mutilation and surplus killing of hosts
Journal of Pest Science, 2018Co-Authors: Ruth Cebolla, Alberto Urbaneja, Pilar Vanaclocha, Alejandro TenaAbstract:An appraisal of the regulatory role of natural enemies on target pests requires the identification of the mechanisms/traits that enhance the ability of an organism to control the density of its prey/host. After stinging herbivore hosts with their ovipositor, hymenopteran parasitoids tend to reject them without ovipositing or host-feeding. Termed pseudoparasitism, the frequency and consequences of this type of attack (hereafter oversting) have been largely disregarded in the hymenopteran parasitoid literature. We choose the parasitoids Aphytis melinus and A. chrysomphali and their common host Aonidiella aurantii as a model system to study this behavior. Using field and laboratory observations, we showed that overstinging is a common behavior in the wild. Under controlled conditions, overstinging occurred more frequently than host-feeding, a behavioral trait that is used to evaluate the potential of parasitoids as biological control agents. Oversting reduced the fecundity and survival of the herbivore host. When we compared between parasitoid species that attack the same host species, the virulence and frequency of this behavior depended on parasitoid species. These results demonstrate that overstinging should be incorporated in the models of host–parasitoid interactions to analyze population dynamics as well as in the future selection of parasitoids for biological control.
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Does host quality dictate the outcome of interference competition between sympatric parasitoids? Effects on their coexistence
Animal Behaviour, 2017Co-Authors: Ruth Cebolla, Alberto Urbaneja, Pablo Bru, Alejandro TenaAbstract:The suitability and quality of herbivorous insect hosts for hymenopteran parasitoids is dynamic, varying with host development. Generally, within a host species, large hosts (i.e. older instars) are considered of higher quality for parasitoid development. Studies of interspecific competition between parasitoids have considered the effect of host instar on indirect competition but its effect on interference competition remains unknown. Here, we report the first results on whether the quality of host instars might dictate the outcome of interference competition between sympatric parasitoids of the genus Aphytis (Hymenoptera: Aphelinidae) when they attack low-quality (second) and high-quality (third) instars of their common host Aonidiella aurantii (Hemiptera: Diaspididae). Oviposition behaviour (host acceptance and clutch size) in low- and high-quality host instars was similar for both Aphytis species in the absence of competition. When they found heterospecific parasitized hosts of high quality, Aphytis melinus laid more eggs and accepted significantly more hosts than Aphytis chrysomphali, whereas there were no significant differences in the low-quality instar. This result suggests that interference competition is mediated by host quality. However, the progeny proportion of both parasitoids in multiparasitized hosts (outcome of competition) was independent of host quality and A. melinus always emerged at higher rates. Therefore, the result of interference competition between these sympatric parasitoids was not affected by host quality and this competition will contribute to the displacement of the native A. chrysomphali by the introduced A. melinus, which has been observed in some areas of the Mediterranean basin.
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Acute toxicity in laboratory tests of fresh and aged residues of pesticides used in citrus on the parasitoid Aphytis melinus
Journal of Pest Science, 2013Co-Authors: P. Vanaclocha, C. Vidal-quist, S. Oheix, Helena Montón, L. Planes, Alejandro Tena, Jordi Catalan, María J Verdú, Alberto UrbanejaAbstract:California red scale Aonidiella aurantii (Maskell) (Hemiptera: Diaspididae) is a worldwide citrus key pest. One of the control strategies currently promoted in the Mediterranean basin is the augmentative release of the parasitoid Aphytis melinus DeBach (Hymenoptera: Aphelinidae). A clear understanding of the impact that pesticides commonly used in citrus have on this parasitoid is therefore essential to assure the efficacy of the method. The aims of this study were to evaluate the lethal effects of freshly applied and laboratory-aged residues of eighteen selected pesticides recommended in IPM for citrus on A. melinus adults. According to their toxicity on A. melinus, the pesticides could be divided in four groups. Etofenprox and chlorpyrifos were harmful and persistent; abamectin was moderately harmful and slightly persistent; dimethoate, chlorpyrifos-methyl, and spirodiclofen were slightly harmful and moderately persistent; and azadirachtin, etoxazole, fenbutaestan, hexythiazox, mancozeb, petroleum oil, pirimicarb, propargite, pymetrozine, pyriproxyfen, spirotetramat, and tebufenpyrad were considered harmless. The information presented here will help us to integrate A. melinus release within an IPM for citrus in which pesticides are still used.
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Acute toxicity in laboratory tests of fresh and aged residues of pesticides used in citrus on the parasitoid Aphytis melinus
Journal of Pest Science, 2013Co-Authors: P. Vanaclocha, C. Vidal-quist, S. Oheix, Helena Montón, L. Planes, Alejandro Tena, Jordi Catalan, María J Verdú, Alberto UrbanejaAbstract:California red scale Aonidiella aurantii (Maskell) (Hemiptera: Diaspididae) is a worldwide citrus key pest. One of the control strategies currently promoted in the Mediterranean basin is the augmentative release of the parasitoid Aphytis melinus DeBach (Hymenoptera: Aphelinidae). A clear understanding of the impact that pesticides commonly used in citrus have on this parasitoid is therefore essential to assure the efficacy of the method. The aims of this study were to evaluate the lethal effects of freshly applied and laboratory-aged residues of eighteen selected pesticides recommended in IPM for citrus on A. melinus adults. According to their toxicity on A. melinus, the pesticides could be divided in four groups. Etofenprox and chlorpyrifos were harmful and persistent; abamectin was moderately harmful and slightly persistent; dimethoate, chlorpyrifos-methyl, and spirodiclofen were slightly harmful and moderately persistent; and azadirachtin, etoxazole, fenbutaestan, hexythiazox, mancozeb, petroleum oil, pirimicarb, propargite, pymetrozine, pyriproxyfen, spirotetramat, and tebufenpyrad were considered harmless. The information presented here will help us to integrate A. melinus release within an IPM for citrus in which pesticides are still used.
Joseph G Morse - One of the best experts on this subject based on the ideXlab platform.
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evaluating the performance and preference of Aphytis melinus hymenoptera aphelinidae on an exotic species acutaspis albopicta hemiptera diaspididae and aonidiella aurantii hemiptera diaspididae
Environmental Entomology, 2016Co-Authors: Lindsay Robinson, Rebeccah Waterworth, Richard A Redak, Joseph G MorseAbstract:Acutaspis albopicta (Cockerell) is an exotic scale detected on imported ‘Hass’ avocados arriving in California from Mexico. An effort was made to understand how well this species might be biologically controlled by the parasitoid, Aphytis melinus DeBach. In no-choice trials, single life stages of A. albopicta and Aonidiella aurantii (Maskell) were exposed to one Ap. melinus female. Ap. melinus attacked and developed to adult on all A. albopicta life stages tested, which included early, middle, and late male and female second instars, and early, middle, and late female third instars. However, the proportion of scales attacked was relatively low (≤20%), as were the number of eggs laid on each scale stage. In six of seven comparisons of scale cover surface area between A. albopicta and Ao. aurantii that were similarly aged, Ao. aurantii was significantly larger. With intraspecific choice trials, females of Ap. melinus strongly preferred to parasitize the oldest and largest female scales in both single- and mixed-sex offerings. Younger, smaller scales were preferred for host feeding. Five comparisons of preference between A. albopicta and Ao. aurantii showed that Ap. melinus preferred 28- and 36-d-old Ao. aurantii females over similarly aged A. albopicta. However, Ap. melinus preferred 23-d-old males of A. albopicta. In three of five comparisons, Ao. aurantii was the preferred species to host feed on. More F1 females of Ap. melinus were recovered from both intraspecific choice trials compared with any stage in no-choice trials. Implications of incorporating Ap. melinus into biological control programs are discussed.
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Cooperators:
2015Co-Authors: Nick C Toscano, Nilima Prabhaker, Joseph G Morse, Timothy J. Henneberry, Steven Castle, Steve NaranjoAbstract:The toxicity of two insect growth regulators (IGRs), buprofezin and pyriproxyfen; three neonicotinoids, acetamiprid, imidacloprid and thiamethoxam; and three conventional insecticides, bifenthrin, fenpropathrin, and chlorpyrifos; were tested in the laboratory for compatibility with egg parasitoids (Gonatocerus ashmeadi, Gonatocerus triguttatus) of glassy-winged sharpshooter (GWSS), Homalodisca coagulata and against Aphytis melinus (A. melinus), an endoparasitoid of armored scale insects found on citrus in California. Most of the selected insecticides tested are used against GWSS and other pests on citrus and grapes. Survivorship of adult parasitoids on citrus leaves with residues of these insecticides (within Petri dishes) was determined after 24, 48 and 72h. Our results indicated that a number of insecticides tested are toxic to the egg parasitoids, Gonatocerus spp., as well as to A. melinus under laboratory conditions. Results from this study allow ranking of the eight insecticides based on their increasing toxicity as follows for Gonatocerus spp.: fenpropathrin> pyriproxyfen> buprofezin> imidacloprid> thiamethoxam> acetamiprid> bifenthrin> chlorpyrifos. All insecticides tested were highly toxic to A. melinus. In additional studies, higher concentrations of imidacloprid and thiamethoxam were found to be toxic over time to two predators, Geocoris punctipes and Orius insidiosus. Results from laboratory studies suggest that both systemics, imidacloprid and thiamethoxam, may not preserve these parasitoids as much as expected. To understand these bioassay results with the two systemics, further studies included the quantification of imidacloprid and thiamethoxam in both th
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COMPATIBILITY OF INSECTICIDES WITH NATURAL ENEMIES OF THE GLASSY-WINGED SHARPSHOOTER
2015Co-Authors: Nick Toscano, Nilima Prabhaker, Steven J Castle, Joseph G Morse, S. NaranjoAbstract:To enhance control of the glassy-winged sharpshooter (GWSS), relative toxicity of neonicotinoids, imidacloprid and thiamethoxam, and other conventional insecticides, chlorpyrifos, cyfluthrin and fenpropathrin, was examined to assess compatibility with parasitoids while being toxic to GWSS. Both imidacloprid and thiamethoxam when applied systemically through uptake in citrus leaves were found to be toxic to adult Gonatocerus ashmeadi and Aphytis melinus. However, systemic treatments of citrus and willow leaves infested with parasitized GWSS eggs did not impact the emergence of parasitoids significantly, suggesting they are relatively safe to the parasitoids while they are within the GWSS eggs. Fenpropathrin, a pyrethroid, was not toxic to G. ashmeadi for 3-4 days post-treatment while chlorpyrifos was quite toxic within 24 h to both G. ashmeadi and A. melinus. Future tests will measure the amounts of imidacloprid and thiamethoxam that are on the surface of citrus leaves affecting the survival of the parasitoids using ELISA. Based on these findings, our research will focus on understanding which chemicals are the most beneficial for maintaining a minimal impact on important parasitoids on citrus and grapes
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discovery of a ci inducing wolbachia and its associated fitness costs in the biological control agent Aphytis melinus debach hymenoptera aphelinidae
Biological Control, 2011Co-Authors: Casandra J. Vasquez, Richard Stouthamer, Gilsang Jeong, Joseph G MorseAbstract:Abstract Wolbachia is an endosymbiotic bacterium that infects a large percentage of arthropods and can affect the fitness of its host. Here we verified for the first time that the biological control agent Aphytis melinus DeBach is infected with a Wolbachia that causes complete cytoplasmic incompatibility, and conducted an insectary and field survey to determine the infection frequency. A. melinus appears to suffer fitness costs associated with infection based on measurements of longevity and fecundity. We also quantified the Wolbachia titers of A. melinus reared at different temperatures and found that, although not completely cured, increased temperature resulted in a significant reduction in the number of Wolbachia copies found in an individual wasp. Implications of our results for biological control are discussed.
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compatibility of two systemic neonicotinoids imidacloprid and thiamethoxam with various natural enemies of agricultural pests
Journal of Economic Entomology, 2011Co-Authors: Nilima Prabhaker, Steven E. Naranjo, Steven J Castle, Nick C Toscano, Joseph G MorseAbstract:ABSTRACT Two systemic neonicotinoids, imidacloprid and thiamethoxam, are widely used for residual control of several insect pests in cotton (Gossypium spp.), vegetables, and citrus (Citrus spp.). We evaluated their impact on six species of beneficial arthropods, including four parasitoid species—Aphytis melinus Debach, Gonatocerus ashmeadi Girault, Eretmocerus eremicus Rose & Zolnerowich, and Encarsia formosa Gahan—and two generalist predators—Geocoris punctipes (Say) and Orius insidiosus (Say)—in the laboratory by using a systemic uptake bioassay. Exposure to systemically treated leaves of both neonicotinoids had negative effects on adult survival in all four parasitoids, with higher potency against A. melinus as indicated by a low LC50. Mortality was also high for G. ashmeadi, E. eremicus, and E. formosa after exposure to both compounds but only after 48 h posttreatment. The two predators G. punctipes and O. insidiosus were variably susceptible to imidacloprid and thiamethoxam after 96-h exposure. Howev...
William W. Murdoch - One of the best experts on this subject based on the ideXlab platform.
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Biological control: lessons from a study of California red scale
Population Ecology, 2006Co-Authors: William W. Murdoch, Susan L Swarbrick, Cherie J. BriggsAbstract:A 20-year study of suppression of California red scale, a world-wide pest of citrus, by the parasitoid Aphytis melinus has established that the interaction is dynamically stable and that the mechanisms leading to control and stability operate at a local scale: spatial processes are not important. Key features appear to be an invulnerable class in the pest and rapid development of the parasitoid compared with the pest, as well as the fact that the parasitoid is an in situ specialist on the pest. Although another parasitoid species and two predator species are also present, they play at most a negligible role in pest control. These features—long-term persistence, suppression by a single natural enemy, an invulnerable stage in the pest and rapid development in the natural enemy—appear to be common in other coccid pest systems. By contrast, in temporary crops where the pest and enemy populations are open (i.e., sustained over the long run mainly by immigration) and non-persistent locally, as is frequently found in aphid pests, we expect that multiple generalist enemies are required for control and, of course, that spatial processes are important. There are very few well-studied examples of such systems, but these support our expectations. In these cases, it also appears that neither rapid enemy development nor an invulnerable pest stage is important for successful control.
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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.
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egg load and the decision to host feed in the parasitoid Aphytis melinus
Journal of Animal Ecology, 1994Co-Authors: Timothy R Collier, William W. Murdoch, Roger M NisbetAbstract:We make and test predictions about how the number of eggs a female parasitoid is carrying (her «egg load») influences her propensity for'host-feeding', the consumption of host body fluids. We first develop a simple dynamic state variable model that predicts that parasitoids should host-feed only when completely empty of eggs. This result reflects an important assumption of the simple model, namely the absence of a delay between host-feeding and the maturation of eggs. We therefore develop two additional models that incorporate a delay by adding extra «pre-egg» state variables to the simple model. Adding even a short delay makes possible a non-zero threshold egg number at and below which the parasitoid host-feeds. We then compare the results of the models with behavioural observations of host-feeding by Aphytis melinus DeBach (Hymenoptera: Aphelinidae)
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POPULATION REGULATION IN THEORY AND PRACTICE
Ecology, 1994Co-Authors: William W. MurdochAbstract:Population regulation is a fundamental process related to most phenomena in ecology, including evolutionary ecology. I review the conceptual basis for defining reg- ulation as bounded fluctuations in abundance, in contrast to the unbounded fluctuations of random-walk populations. Regulation arises as a result of potentially stabilizing density- dependent processes, even when brought about by "non-equilibrium" mechanisms. Al- though the phenomenon is unambiguous in theory, detecting regulation by finding evidence for density dependence in a series of population estimates faces unsolved statistical prob- lems. So, while there is growing evidence for widespread regulation, severe detection prob- lems remain. I illustrate these with data from bird populations. Whether regulation is typically achieved by local stabilizing mechanisms or via metapopulation dynamics remains to be determined. I summarize recent studies on a particularly well-regulated system - red scale (Aonidiella aurantii) and its controlling parasitoid, Aphytis melinus. We tested and failed to find evidence for eight hypotheses that might account for the system's stability, including spatial heterogeneity in attack rates, a refuge, and metapopulation dynamics. We also failed to find evidence for density-dependent parasitism, but such density dependence might be still size-structured~rthu host.eipen
P. Vanaclocha - One of the best experts on this subject based on the ideXlab platform.
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Acute toxicity in laboratory tests of fresh and aged residues of pesticides used in citrus on the parasitoid Aphytis melinus
Journal of Pest Science, 2013Co-Authors: P. Vanaclocha, C. Vidal-quist, S. Oheix, Helena Montón, L. Planes, Alejandro Tena, Jordi Catalan, María J Verdú, Alberto UrbanejaAbstract:California red scale Aonidiella aurantii (Maskell) (Hemiptera: Diaspididae) is a worldwide citrus key pest. One of the control strategies currently promoted in the Mediterranean basin is the augmentative release of the parasitoid Aphytis melinus DeBach (Hymenoptera: Aphelinidae). A clear understanding of the impact that pesticides commonly used in citrus have on this parasitoid is therefore essential to assure the efficacy of the method. The aims of this study were to evaluate the lethal effects of freshly applied and laboratory-aged residues of eighteen selected pesticides recommended in IPM for citrus on A. melinus adults. According to their toxicity on A. melinus, the pesticides could be divided in four groups. Etofenprox and chlorpyrifos were harmful and persistent; abamectin was moderately harmful and slightly persistent; dimethoate, chlorpyrifos-methyl, and spirodiclofen were slightly harmful and moderately persistent; and azadirachtin, etoxazole, fenbutaestan, hexythiazox, mancozeb, petroleum oil, pirimicarb, propargite, pymetrozine, pyriproxyfen, spirotetramat, and tebufenpyrad were considered harmless. The information presented here will help us to integrate A. melinus release within an IPM for citrus in which pesticides are still used.
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Acute toxicity in laboratory tests of fresh and aged residues of pesticides used in citrus on the parasitoid Aphytis melinus
Journal of Pest Science, 2013Co-Authors: P. Vanaclocha, C. Vidal-quist, S. Oheix, Helena Montón, L. Planes, Alejandro Tena, Jordi Catalan, María J Verdú, Alberto UrbanejaAbstract:California red scale Aonidiella aurantii (Maskell) (Hemiptera: Diaspididae) is a worldwide citrus key pest. One of the control strategies currently promoted in the Mediterranean basin is the augmentative release of the parasitoid Aphytis melinus DeBach (Hymenoptera: Aphelinidae). A clear understanding of the impact that pesticides commonly used in citrus have on this parasitoid is therefore essential to assure the efficacy of the method. The aims of this study were to evaluate the lethal effects of freshly applied and laboratory-aged residues of eighteen selected pesticides recommended in IPM for citrus on A. melinus adults. According to their toxicity on A. melinus, the pesticides could be divided in four groups. Etofenprox and chlorpyrifos were harmful and persistent; abamectin was moderately harmful and slightly persistent; dimethoate, chlorpyrifos-methyl, and spirodiclofen were slightly harmful and moderately persistent; and azadirachtin, etoxazole, fenbutaestan, hexythiazox, mancozeb, petroleum oil, pirimicarb, propargite, pymetrozine, pyriproxyfen, spirotetramat, and tebufenpyrad were considered harmless. The information presented here will help us to integrate A. melinus release within an IPM for citrus in which pesticides are still used.