Volatile organic compounds (VOCs) are emitted from all plants and these VOCs are important means ... more Volatile organic compounds (VOCs) are emitted from all plants and these VOCs are important means of communication between plants and insects. It has been documented that pathogen infections alter VOC profiles rendering infected plants more attractive to specific vectors transmitting these pathogens than uninfected plants, thus potentially aiding in pathogen propagation. Mimicking these chemical cues might enable insect attraction away from the plant or disruption of host finding behavior of the vector. However, the practical implications have not been fully explored. We used citrus, Diaphorina citri and huanglongbing (HLB) as a model host-vector-disease system because HLB threatens citrus production worldwide and is similar to other critical diseases of food crops, such as Zebra Chip affecting potato. We formulated a synthetic chemical blend using selected HLB-specific biomarker compounds, and tested the blend with the Attenu assay system for chemosensory proteins. The Attenu assay system is a procedure that identifies interactions between insect chemosensory proteins and their ligands. We found that mixtures of compounds mimicking the volatile profile of HLB-infected citrus can be bound by chemosensory proteins. Further investigation of these blends in laboratory behavioral assays resulted in development of a synthetic lure that was more attractive to D. citri than natural citrus tree volatiles. This strategy could provide a new route to produce chemical lures for vector population control for a variety of plant and/or animal systems and it may result in the development of a practical lure for monitoring vectors of disease, such as D. citri.
Although specialist herbivorous insects are guided by innate responses to host plant cues, host p... more Although specialist herbivorous insects are guided by innate responses to host plant cues, host plant preference may be influenced by experience and is not dictated by instinct alone. The effect of learning on host plant preference was examined in the Asian citrus psyllid, Diaphorina citri; vector of the causal agent of citrus greening disease or huanglongbing. We investigated: a) whether development on specific host plant species influenced host plant preference in mature D. citri; and b) the extent of associative learning in D. citri in the form of simple and compound conditioning. Learning was measured by cue selection in a 2-choice behavioral assay and compared to naïve controls. Our results showed that learned responses in D. citri are complex and diverse. The developmental host plant species influenced adult host plant preference, with female psyllids preferring the species on which they were reared. However, such preferences were subject to change with the introduction of an alternative host plant within 24-48 hrs, indicating a large degree of experience-dependent response plasticity. Additionally, learning occurred for multiple sensory modalities where novel olfactory and visual environmental cues were associated with the host plant. However, males and females displayed differing discriminatory abilities. In compound conditioning tasks, males exhibited recognition of a compound stimulus alone while females were capable of learning the individual components. These findings suggest D. citri are dynamic animals that demonstrate host plant preference based on developmental and adult experience and can learn to recognize olfactory and visual host plant stimuli in ways that may be sex specific. These experience-based associations are likely used by adults to locate and select suitable host plants for feeding and reproduction and may suggest the need for more tailored lures and traps, which reflect region-specific cultivars or predominate Rutaceae in the area being monitored.
The effects of increasing female density on Asian citrus psyllid (ACP) [Diaphorina citri Kuwayama... more The effects of increasing female density on Asian citrus psyllid (ACP) [Diaphorina citri Kuwayama (Hemiptera: Liviidae)] behavior were investigated. In four-choice assays, female ACP avoided settling on citrus seedlings that were previously pre-infested with a high density of conspecific females. In olfactometer bioassays, headspace volatiles from ten female ACP were repellent to conspecific females. In a subsequent experiment, the upper canopy of citrus seedlings was confined within glass domes and isolated from the lower canopy with a polytetrafluoroethylene guillotine. These glass domes were attached to a two-choice olfactometer such that only the headspace volatiles of the upper canopy were connected to the arms of the olfactometer. For the first treatment, ACP females were placed in the upper canopy. In this case, conspecific females introduced into the olfactometer did not show preference between volatiles from the damaged plant containing female ACP versus a blank control. In...
We have investigated the chemical ecology of the redbay ambrosia beetle Xyleborus glabratus. Xyle... more We have investigated the chemical ecology of the redbay ambrosia beetle Xyleborus glabratus. Xyleborus glabratus, is an invasive wood boring beetle that has become established in the southeastern United States and transmits a fungus, Raffaelea lauricola, that causes lethal laurel wilt. We developed a novel laboratory bioassay to test the response of ambrosia beetles to volatiles. This bioassay uses a 4-ways olfactometer where each arms are connected to a different odor source. We first tested the hypothesis that leaf volatiles may cause differential beetle response and allowed redbay ambrosia beetle to differentiate hosts (redbay and swampbay) from non-hosts (oak). We found that redbay and swampbay volatiles were strongly attractant to ambrosia beetles, whereas non-host volatiles were not. Subsequently we explored whether leaf volatiles play a role in the occurrence of ‘escape trees’ – trees that remain living in forest where redbays were otherwise killed by the fungal pathogen tran...
In the context of a vector-borne pathogen system, the spread of disease depends on movement of ve... more In the context of a vector-borne pathogen system, the spread of disease depends on movement of vectors across a landscape. We examined the flight capability of the Asian citrus psyllid (Diphorina citri Kuwayama, Hemiptera: Liviidae) with a laboratory flight mill. D. citri is the vector of the bacterial pathogen Candidatus Liberibacter asiaticus (CLas) potentially causing huanglongbing or citrus greening disease. Initially, we compared the flight capability of D. citri depending on their sex and morphotype (color of abdomen). Two general morphotypes exist within this species: green/blue and gray/brown. We observed that approximately 32% of psyllids from the green/blue morphotype tested exhibited long durations of flight (> 60 s); whereas; less than 5% of psyllids from the gray/brown morphotype performed such long duration flights. There was no difference in flight performance between the two sexes within both the gray/brown and green/blue morphotypes. We measured pronotum width an...
The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Liviidae), is the vector of... more The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Liviidae), is the vector of the bacterial pathogen, ‘Candidatus Liberibacter asiaticus’ (Las), which is the putative causal agent of huanglongbing (HLB) in citrus. Las infection induces the release of a specific volatile (methyl salicylate) that attracts ACP. In this study, we investigated how infection status of plants (both symptomatic and asymptomatic) affects ACP host acceptance. We also investigated the effect of foliar nutrient applications, which are currently used to reduce HLB disease symptoms and increase yield production of Las-infected citrus, on ACP behavior. In laboratory bioassays, ACP preferentially settled on infected citrus plants over uninfected controls, but this preference was greater when the infected plants were asymptomatic as compared with those showing symptoms of HLB. However, the symptomatic citrus plants that received supplemental foliar nutrient sprays were as attractive to ACP as asy...
The redbay ambrosia beetle, Xyleborus glabratus, is an important pest of redbay (Persea borbonia)... more The redbay ambrosia beetle, Xyleborus glabratus, is an important pest of redbay (Persea borbonia) and swamp bay (P. palustris) trees in forests of the southeastern USA. It is also a threat to commercially grown avocado. The beetle is attracted to host wood volatiles, particularly sesquiterpenes. Contrary to other ambrosia beetles that attack stressed, possibly pathogen-infected, and dying trees, X. glabratus readily attacks healthy trees. To date little is known about the role of leaf volatiles in the host selection behavior and ecology of X. glabratus. To address this question, an olfactometer bioassay was developed to test the behavioral response of X. glabratus to plant leaf volatiles. We found that X. glabratus was attracted to the leaf odors of their hosts, redbay and swamp bay, with no attraction to a non-host tree tested (live oak, Quercus virginiana), which served as a negative control. Gas chromatography-mass spectrometry (GS/MS) analysis of leaves revealed the absence of s...
Présentée et soutenue par Xavier MARTINI Le 29 Janvier 2010 Titre : Evolution du cannibalisme et ... more Présentée et soutenue par Xavier MARTINI Le 29 Janvier 2010 Titre : Evolution du cannibalisme et du comportement de ponte chez les coccinelles aphidiphages. Je voudrais tout d'abord remercier Jean-louis Hemptinne de m'avoir accueilli il y a quelques années de cela dans le Laboratoire d'Agro-Ecologie de l'ENFAT. Je le remercie pour m'avoir permis de faire cette thèse, et de m'avoir encadré. J'ai particulièrement apprécié la liberté dont j'ai bénéficié pour mener mon projet de recherche, et de la confiance qu'il m'a accordée tout au long de ces 3 ans. Je remercie également Isabelle Olivieri pour son co-encadrement, et pour m'avoir accueilli à Montpellier. Je la remercie particulièrement pour ses conseils et ses suggestions qui m'ont permis d'avancer énormément dans mon travail. Je remercie bien entendu Patsy Haccou pour sa patience, et pour toute l'aide apportée sur la partie de modélisation. Je la remercie pour son accueil à Leiden, un séjour qui restera un des meilleurs souvenirs de ma thèse. Je remercie Alexandra pour ses conseils, et pour les discussions passionnées autour d'une tasse de thé… Je remercie mes collègues thèsards et post doctorants : Abdoulay, Achille, Elsa, Julie, Raphael, et bien sûr Aurelie pour les gâteaux de la pause café ! Je remercie les stagiaires qui m'ont assisté lors de certaines expériences : Thomas, Benoit et Rana. Je remercie mes parents et ma famille pour leur soutien sans faille, et leurs encouragements.
Interactions between plant pathogens and arthropods have been predominantly studied through the p... more Interactions between plant pathogens and arthropods have been predominantly studied through the prism of herbivorous arthropods. Currently, little is known about the effect of plant pathogens on the third trophic level. This question is particularly interesting in cases where pathogens manipulate host phenotype to increase vector attraction and presumably increase their own proliferation. Indeed, a predator or a parasitoid of a vector may take advantage of this manipulated phenotype to increase its foraging performance. We explored the case of a bacterial pathogen, Candidatus Liberibacter asiaticus (Las), which modifies the odors released by its host plant (citrus trees) to attract its vector, the psyllid Diaphorina citri. We found that the specialist parasitoid of D. citri, Tamarixia radiata, was attracted more toward Las-infected than uninfected plants. We demonstrated that this attractiveness was due to the release of methyl salicylate. Parasitization of D. citri nymphs on Las-infected plants was higher than on uninfected controls. Also, parasitization was higher on uninfected plants baited with methyl salicylate than on non-baited controls. This is the first report of a parasitoid "eavesdropping" on a plant volatile induced by bacterial pathogen infection, which also increases effectiveness of host seeking behavior of its herbivorous vector.
1 In cotton fields in Texas, spider mites are sporadic pests, whereas thrips are considered as ma... more 1 In cotton fields in Texas, spider mites are sporadic pests, whereas thrips are considered as major pests on early stages (before the fourth true leaf stage). Thrips are also important predators of spider mite eggs. In the present study, we tested the hypothesis that the presence of spider mites on seedling cotton may increase the likelihood of the occurrence of thrips. 2 Based on a greenhouse experiment, it was confirmed that seedling cotton was a suitable host for spider mites. Subsequently, we conducted a 2-year field experiment in which we studied the likelihood of thrips infestation in cotton plants with/without experimental spider mite infestations. 3 Spider mites established better in 2011 (dry and hot season) than in 2010 (rainy and cooler season), and there was a positive association between spider mites on cotton plants and natural thrips infestation. Thus, we showed that the probability of thrips infestation strongly increased with the presence of spider mites. 4 To confirm the proposed hypothesis on a larger scale, a second field experiment was performed, in which one half of a field was infested with spider mites. Weekly sampling of thrips and spider mites showed a two-fold increase of thrips immatures on plots previously infested with spider mites. 5 The results obtained in the present study emphasize the importance of incorporating spider mite population dynamics into risk assessments of thrips infestation in seedling cotton fields in Texas and elsewhere.
Volatile organic compounds (VOCs) are emitted from all plants and these VOCs are important means ... more Volatile organic compounds (VOCs) are emitted from all plants and these VOCs are important means of communication between plants and insects. It has been documented that pathogen infections alter VOC profiles rendering infected plants more attractive to specific vectors transmitting these pathogens than uninfected plants, thus potentially aiding in pathogen propagation. Mimicking these chemical cues might enable insect attraction away from the plant or disruption of host finding behavior of the vector. However, the practical implications have not been fully explored. We used citrus, Diaphorina citri and huanglongbing (HLB) as a model host-vector-disease system because HLB threatens citrus production worldwide and is similar to other critical diseases of food crops, such as Zebra Chip affecting potato. We formulated a synthetic chemical blend using selected HLB-specific biomarker compounds, and tested the blend with the Attenu assay system for chemosensory proteins. The Attenu assay system is a procedure that identifies interactions between insect chemosensory proteins and their ligands. We found that mixtures of compounds mimicking the volatile profile of HLB-infected citrus can be bound by chemosensory proteins. Further investigation of these blends in laboratory behavioral assays resulted in development of a synthetic lure that was more attractive to D. citri than natural citrus tree volatiles. This strategy could provide a new route to produce chemical lures for vector population control for a variety of plant and/or animal systems and it may result in the development of a practical lure for monitoring vectors of disease, such as D. citri.
Larvae of aphidophagous ladybirds leave a cue in their tracks that deters oviposition. The influe... more Larvae of aphidophagous ladybirds leave a cue in their tracks that deters oviposition. The influence of relatedness on this behaviour is for the first time explored in this paper. Two-spot ladybird females (Adalia bipunctata L.) under different conditions (young and naive, young and experienced, and old and naive) were exposed either to (i) clean filter paper, (ii) filter paper contaminated with unrelated larval tracks or (iii) filter paper contaminated with related larval tracks from their offspring. Oviposition time was recorded during nine hours. Oviposition was inhibited by larval tracks, and was more so by related than unrelated ones. Experienced females showed the same behaviour but with lower intensity. With old females, response was not significant with any type of larval tracks. This is the first report of the effect of relatedness on a ladybird's response to larval tracks.
Development of effective management practices for insect pests relies heavily on sampling methods... more Development of effective management practices for insect pests relies heavily on sampling methods to accurately detect and quantify emerging populations. Herein we describe a novel method to extract and count nymphs of potato psyllid, Bactericera cockerelli (Šulc) (Hemiptera: Triozidae), from leaves in commercial fields of potato, Solanum tuberosum L. (Solanaceae). The proposed sampling method (referred to as the leaf washing method, LWM) consists of: (1) immersing samples of infested leaves in cold water to remove dust and sand; (2) immersing leaves in >85°C water for 5 s; (3) extracting psyllid nymphs from heated water by passing it through a sampling unit composed of a funnel with a fine mesh-organza fabric inside and attached to a vacuum pump; and (4) removing organza fabric and count psyllid nymphs under a stereoscope. With five sampling units operating simultaneously, one person is able to process and count immatures from about 400 leaf samples in two normal work days. As examples of applications, the LWM was used to characterize: (1) the vertical distribution of potato psyllid nymphs in the potato canopy; and (2) the spatio-temporal distribution of potato psyllid nymphs in three potato varieties. Using LWM, we showed that psyllid nymphs were most predominant in the middle portion of the canopy and that spatio-temporal distributions of nymphs varied among potato varieties.
1. Egg cannibalism by larvae is common in Coccinellidae and is known to be advantageous for the c... more 1. Egg cannibalism by larvae is common in Coccinellidae and is known to be advantageous for the cannibals. Furthermore, larvae of aphidophagous ladybirds usually produce an ovipositiondeterring pheromone (ODP), which inhibits oviposition by adult females. It has been proposed that the response to ODP has evolved because of the high costs of cannibalism. However, this has never been formally proved. 2. In this paper, we study the theoretical evolution of this system. We first look at the conditions under which cannibalism and the response to ODP can evolve. Subsequently, we examine the occurrence of polymorphism both in the production of larval tracks and in the sensitivity of females to specific pheromones. 3. The models predict that the amount of cannibalism should not depend on prey density and that evolution should lead to a continuous increase in cannibalism, and consequently larvae should always cannibalize eggs when possible. In response to the cost of cannibalism, ODP recognition can evolve, so that females avoid laying eggs in patches of prey already occupied by conspecific larvae. The result is an arms race between larvae and adult females, which favours a diversification of ODP pheromones. Our models show that: (i) females should be able to recognize mixtures of hydrocarbons rather than a single molecule; and (ii) females should be more sensitive to the tracks of their own offspring than those of non-related larvae.
Volatile organic compounds (VOCs) are emitted from all plants and these VOCs are important means ... more Volatile organic compounds (VOCs) are emitted from all plants and these VOCs are important means of communication between plants and insects. It has been documented that pathogen infections alter VOC profiles rendering infected plants more attractive to specific vectors transmitting these pathogens than uninfected plants, thus potentially aiding in pathogen propagation. Mimicking these chemical cues might enable insect attraction away from the plant or disruption of host finding behavior of the vector. However, the practical implications have not been fully explored. We used citrus, Diaphorina citri and huanglongbing (HLB) as a model host-vector-disease system because HLB threatens citrus production worldwide and is similar to other critical diseases of food crops, such as Zebra Chip affecting potato. We formulated a synthetic chemical blend using selected HLB-specific biomarker compounds, and tested the blend with the Attenu assay system for chemosensory proteins. The Attenu assay system is a procedure that identifies interactions between insect chemosensory proteins and their ligands. We found that mixtures of compounds mimicking the volatile profile of HLB-infected citrus can be bound by chemosensory proteins. Further investigation of these blends in laboratory behavioral assays resulted in development of a synthetic lure that was more attractive to D. citri than natural citrus tree volatiles. This strategy could provide a new route to produce chemical lures for vector population control for a variety of plant and/or animal systems and it may result in the development of a practical lure for monitoring vectors of disease, such as D. citri.
Although specialist herbivorous insects are guided by innate responses to host plant cues, host p... more Although specialist herbivorous insects are guided by innate responses to host plant cues, host plant preference may be influenced by experience and is not dictated by instinct alone. The effect of learning on host plant preference was examined in the Asian citrus psyllid, Diaphorina citri; vector of the causal agent of citrus greening disease or huanglongbing. We investigated: a) whether development on specific host plant species influenced host plant preference in mature D. citri; and b) the extent of associative learning in D. citri in the form of simple and compound conditioning. Learning was measured by cue selection in a 2-choice behavioral assay and compared to naïve controls. Our results showed that learned responses in D. citri are complex and diverse. The developmental host plant species influenced adult host plant preference, with female psyllids preferring the species on which they were reared. However, such preferences were subject to change with the introduction of an alternative host plant within 24-48 hrs, indicating a large degree of experience-dependent response plasticity. Additionally, learning occurred for multiple sensory modalities where novel olfactory and visual environmental cues were associated with the host plant. However, males and females displayed differing discriminatory abilities. In compound conditioning tasks, males exhibited recognition of a compound stimulus alone while females were capable of learning the individual components. These findings suggest D. citri are dynamic animals that demonstrate host plant preference based on developmental and adult experience and can learn to recognize olfactory and visual host plant stimuli in ways that may be sex specific. These experience-based associations are likely used by adults to locate and select suitable host plants for feeding and reproduction and may suggest the need for more tailored lures and traps, which reflect region-specific cultivars or predominate Rutaceae in the area being monitored.
The effects of increasing female density on Asian citrus psyllid (ACP) [Diaphorina citri Kuwayama... more The effects of increasing female density on Asian citrus psyllid (ACP) [Diaphorina citri Kuwayama (Hemiptera: Liviidae)] behavior were investigated. In four-choice assays, female ACP avoided settling on citrus seedlings that were previously pre-infested with a high density of conspecific females. In olfactometer bioassays, headspace volatiles from ten female ACP were repellent to conspecific females. In a subsequent experiment, the upper canopy of citrus seedlings was confined within glass domes and isolated from the lower canopy with a polytetrafluoroethylene guillotine. These glass domes were attached to a two-choice olfactometer such that only the headspace volatiles of the upper canopy were connected to the arms of the olfactometer. For the first treatment, ACP females were placed in the upper canopy. In this case, conspecific females introduced into the olfactometer did not show preference between volatiles from the damaged plant containing female ACP versus a blank control. In...
We have investigated the chemical ecology of the redbay ambrosia beetle Xyleborus glabratus. Xyle... more We have investigated the chemical ecology of the redbay ambrosia beetle Xyleborus glabratus. Xyleborus glabratus, is an invasive wood boring beetle that has become established in the southeastern United States and transmits a fungus, Raffaelea lauricola, that causes lethal laurel wilt. We developed a novel laboratory bioassay to test the response of ambrosia beetles to volatiles. This bioassay uses a 4-ways olfactometer where each arms are connected to a different odor source. We first tested the hypothesis that leaf volatiles may cause differential beetle response and allowed redbay ambrosia beetle to differentiate hosts (redbay and swampbay) from non-hosts (oak). We found that redbay and swampbay volatiles were strongly attractant to ambrosia beetles, whereas non-host volatiles were not. Subsequently we explored whether leaf volatiles play a role in the occurrence of ‘escape trees’ – trees that remain living in forest where redbays were otherwise killed by the fungal pathogen tran...
In the context of a vector-borne pathogen system, the spread of disease depends on movement of ve... more In the context of a vector-borne pathogen system, the spread of disease depends on movement of vectors across a landscape. We examined the flight capability of the Asian citrus psyllid (Diphorina citri Kuwayama, Hemiptera: Liviidae) with a laboratory flight mill. D. citri is the vector of the bacterial pathogen Candidatus Liberibacter asiaticus (CLas) potentially causing huanglongbing or citrus greening disease. Initially, we compared the flight capability of D. citri depending on their sex and morphotype (color of abdomen). Two general morphotypes exist within this species: green/blue and gray/brown. We observed that approximately 32% of psyllids from the green/blue morphotype tested exhibited long durations of flight (> 60 s); whereas; less than 5% of psyllids from the gray/brown morphotype performed such long duration flights. There was no difference in flight performance between the two sexes within both the gray/brown and green/blue morphotypes. We measured pronotum width an...
The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Liviidae), is the vector of... more The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Liviidae), is the vector of the bacterial pathogen, ‘Candidatus Liberibacter asiaticus’ (Las), which is the putative causal agent of huanglongbing (HLB) in citrus. Las infection induces the release of a specific volatile (methyl salicylate) that attracts ACP. In this study, we investigated how infection status of plants (both symptomatic and asymptomatic) affects ACP host acceptance. We also investigated the effect of foliar nutrient applications, which are currently used to reduce HLB disease symptoms and increase yield production of Las-infected citrus, on ACP behavior. In laboratory bioassays, ACP preferentially settled on infected citrus plants over uninfected controls, but this preference was greater when the infected plants were asymptomatic as compared with those showing symptoms of HLB. However, the symptomatic citrus plants that received supplemental foliar nutrient sprays were as attractive to ACP as asy...
The redbay ambrosia beetle, Xyleborus glabratus, is an important pest of redbay (Persea borbonia)... more The redbay ambrosia beetle, Xyleborus glabratus, is an important pest of redbay (Persea borbonia) and swamp bay (P. palustris) trees in forests of the southeastern USA. It is also a threat to commercially grown avocado. The beetle is attracted to host wood volatiles, particularly sesquiterpenes. Contrary to other ambrosia beetles that attack stressed, possibly pathogen-infected, and dying trees, X. glabratus readily attacks healthy trees. To date little is known about the role of leaf volatiles in the host selection behavior and ecology of X. glabratus. To address this question, an olfactometer bioassay was developed to test the behavioral response of X. glabratus to plant leaf volatiles. We found that X. glabratus was attracted to the leaf odors of their hosts, redbay and swamp bay, with no attraction to a non-host tree tested (live oak, Quercus virginiana), which served as a negative control. Gas chromatography-mass spectrometry (GS/MS) analysis of leaves revealed the absence of s...
Présentée et soutenue par Xavier MARTINI Le 29 Janvier 2010 Titre : Evolution du cannibalisme et ... more Présentée et soutenue par Xavier MARTINI Le 29 Janvier 2010 Titre : Evolution du cannibalisme et du comportement de ponte chez les coccinelles aphidiphages. Je voudrais tout d'abord remercier Jean-louis Hemptinne de m'avoir accueilli il y a quelques années de cela dans le Laboratoire d'Agro-Ecologie de l'ENFAT. Je le remercie pour m'avoir permis de faire cette thèse, et de m'avoir encadré. J'ai particulièrement apprécié la liberté dont j'ai bénéficié pour mener mon projet de recherche, et de la confiance qu'il m'a accordée tout au long de ces 3 ans. Je remercie également Isabelle Olivieri pour son co-encadrement, et pour m'avoir accueilli à Montpellier. Je la remercie particulièrement pour ses conseils et ses suggestions qui m'ont permis d'avancer énormément dans mon travail. Je remercie bien entendu Patsy Haccou pour sa patience, et pour toute l'aide apportée sur la partie de modélisation. Je la remercie pour son accueil à Leiden, un séjour qui restera un des meilleurs souvenirs de ma thèse. Je remercie Alexandra pour ses conseils, et pour les discussions passionnées autour d'une tasse de thé… Je remercie mes collègues thèsards et post doctorants : Abdoulay, Achille, Elsa, Julie, Raphael, et bien sûr Aurelie pour les gâteaux de la pause café ! Je remercie les stagiaires qui m'ont assisté lors de certaines expériences : Thomas, Benoit et Rana. Je remercie mes parents et ma famille pour leur soutien sans faille, et leurs encouragements.
Interactions between plant pathogens and arthropods have been predominantly studied through the p... more Interactions between plant pathogens and arthropods have been predominantly studied through the prism of herbivorous arthropods. Currently, little is known about the effect of plant pathogens on the third trophic level. This question is particularly interesting in cases where pathogens manipulate host phenotype to increase vector attraction and presumably increase their own proliferation. Indeed, a predator or a parasitoid of a vector may take advantage of this manipulated phenotype to increase its foraging performance. We explored the case of a bacterial pathogen, Candidatus Liberibacter asiaticus (Las), which modifies the odors released by its host plant (citrus trees) to attract its vector, the psyllid Diaphorina citri. We found that the specialist parasitoid of D. citri, Tamarixia radiata, was attracted more toward Las-infected than uninfected plants. We demonstrated that this attractiveness was due to the release of methyl salicylate. Parasitization of D. citri nymphs on Las-infected plants was higher than on uninfected controls. Also, parasitization was higher on uninfected plants baited with methyl salicylate than on non-baited controls. This is the first report of a parasitoid "eavesdropping" on a plant volatile induced by bacterial pathogen infection, which also increases effectiveness of host seeking behavior of its herbivorous vector.
1 In cotton fields in Texas, spider mites are sporadic pests, whereas thrips are considered as ma... more 1 In cotton fields in Texas, spider mites are sporadic pests, whereas thrips are considered as major pests on early stages (before the fourth true leaf stage). Thrips are also important predators of spider mite eggs. In the present study, we tested the hypothesis that the presence of spider mites on seedling cotton may increase the likelihood of the occurrence of thrips. 2 Based on a greenhouse experiment, it was confirmed that seedling cotton was a suitable host for spider mites. Subsequently, we conducted a 2-year field experiment in which we studied the likelihood of thrips infestation in cotton plants with/without experimental spider mite infestations. 3 Spider mites established better in 2011 (dry and hot season) than in 2010 (rainy and cooler season), and there was a positive association between spider mites on cotton plants and natural thrips infestation. Thus, we showed that the probability of thrips infestation strongly increased with the presence of spider mites. 4 To confirm the proposed hypothesis on a larger scale, a second field experiment was performed, in which one half of a field was infested with spider mites. Weekly sampling of thrips and spider mites showed a two-fold increase of thrips immatures on plots previously infested with spider mites. 5 The results obtained in the present study emphasize the importance of incorporating spider mite population dynamics into risk assessments of thrips infestation in seedling cotton fields in Texas and elsewhere.
Volatile organic compounds (VOCs) are emitted from all plants and these VOCs are important means ... more Volatile organic compounds (VOCs) are emitted from all plants and these VOCs are important means of communication between plants and insects. It has been documented that pathogen infections alter VOC profiles rendering infected plants more attractive to specific vectors transmitting these pathogens than uninfected plants, thus potentially aiding in pathogen propagation. Mimicking these chemical cues might enable insect attraction away from the plant or disruption of host finding behavior of the vector. However, the practical implications have not been fully explored. We used citrus, Diaphorina citri and huanglongbing (HLB) as a model host-vector-disease system because HLB threatens citrus production worldwide and is similar to other critical diseases of food crops, such as Zebra Chip affecting potato. We formulated a synthetic chemical blend using selected HLB-specific biomarker compounds, and tested the blend with the Attenu assay system for chemosensory proteins. The Attenu assay system is a procedure that identifies interactions between insect chemosensory proteins and their ligands. We found that mixtures of compounds mimicking the volatile profile of HLB-infected citrus can be bound by chemosensory proteins. Further investigation of these blends in laboratory behavioral assays resulted in development of a synthetic lure that was more attractive to D. citri than natural citrus tree volatiles. This strategy could provide a new route to produce chemical lures for vector population control for a variety of plant and/or animal systems and it may result in the development of a practical lure for monitoring vectors of disease, such as D. citri.
Larvae of aphidophagous ladybirds leave a cue in their tracks that deters oviposition. The influe... more Larvae of aphidophagous ladybirds leave a cue in their tracks that deters oviposition. The influence of relatedness on this behaviour is for the first time explored in this paper. Two-spot ladybird females (Adalia bipunctata L.) under different conditions (young and naive, young and experienced, and old and naive) were exposed either to (i) clean filter paper, (ii) filter paper contaminated with unrelated larval tracks or (iii) filter paper contaminated with related larval tracks from their offspring. Oviposition time was recorded during nine hours. Oviposition was inhibited by larval tracks, and was more so by related than unrelated ones. Experienced females showed the same behaviour but with lower intensity. With old females, response was not significant with any type of larval tracks. This is the first report of the effect of relatedness on a ladybird's response to larval tracks.
Development of effective management practices for insect pests relies heavily on sampling methods... more Development of effective management practices for insect pests relies heavily on sampling methods to accurately detect and quantify emerging populations. Herein we describe a novel method to extract and count nymphs of potato psyllid, Bactericera cockerelli (Šulc) (Hemiptera: Triozidae), from leaves in commercial fields of potato, Solanum tuberosum L. (Solanaceae). The proposed sampling method (referred to as the leaf washing method, LWM) consists of: (1) immersing samples of infested leaves in cold water to remove dust and sand; (2) immersing leaves in >85°C water for 5 s; (3) extracting psyllid nymphs from heated water by passing it through a sampling unit composed of a funnel with a fine mesh-organza fabric inside and attached to a vacuum pump; and (4) removing organza fabric and count psyllid nymphs under a stereoscope. With five sampling units operating simultaneously, one person is able to process and count immatures from about 400 leaf samples in two normal work days. As examples of applications, the LWM was used to characterize: (1) the vertical distribution of potato psyllid nymphs in the potato canopy; and (2) the spatio-temporal distribution of potato psyllid nymphs in three potato varieties. Using LWM, we showed that psyllid nymphs were most predominant in the middle portion of the canopy and that spatio-temporal distributions of nymphs varied among potato varieties.
1. Egg cannibalism by larvae is common in Coccinellidae and is known to be advantageous for the c... more 1. Egg cannibalism by larvae is common in Coccinellidae and is known to be advantageous for the cannibals. Furthermore, larvae of aphidophagous ladybirds usually produce an ovipositiondeterring pheromone (ODP), which inhibits oviposition by adult females. It has been proposed that the response to ODP has evolved because of the high costs of cannibalism. However, this has never been formally proved. 2. In this paper, we study the theoretical evolution of this system. We first look at the conditions under which cannibalism and the response to ODP can evolve. Subsequently, we examine the occurrence of polymorphism both in the production of larval tracks and in the sensitivity of females to specific pheromones. 3. The models predict that the amount of cannibalism should not depend on prey density and that evolution should lead to a continuous increase in cannibalism, and consequently larvae should always cannibalize eggs when possible. In response to the cost of cannibalism, ODP recognition can evolve, so that females avoid laying eggs in patches of prey already occupied by conspecific larvae. The result is an arms race between larvae and adult females, which favours a diversification of ODP pheromones. Our models show that: (i) females should be able to recognize mixtures of hydrocarbons rather than a single molecule; and (ii) females should be more sensitive to the tracks of their own offspring than those of non-related larvae.
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Papers by Xavier Martini