Valerie Fournier

University of California, Davis, Davis, CA, United States

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Publications (16)17.47 Total impact

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    ABSTRACT: Induced plant responses to herbivores and pathogens have been found in many systems. We examined intra- and interspecific interactions among three parasites through induced responses in their shared host plant, papaya. Three key parasites attack papaya foliage in Hawaii: the carmine spider mite, Tetranychus cinnabarinus (Boisduval); the papaya rust mite, Calacarus flagelliseta Fletchmann, De Moraes, and Barbosa; and the powdery mildew causal agent, Oidium caricae F. Noack. Under laboratory conditions, papaya seedlings were first exposed to standardized populations of mites and mildew; the parasites were removed, and the clean, previously infested plants were transplanted into the field to be exposed to colonization by natural populations of plant parasites. Population growth of colonizers was monitored for a period of 3 mo. We found no evidence for induced plant resistance. Rather, our results suggest that papaya expresses a weak form of induced susceptibility after injury from papaya rust mites and powdery mildew. Plants exposed to rust mites as young seedlings subsequently supported larger populations of spider mites, and plants exposed early to powdery mildew subsequently supported larger populations of rust mites.
    Environmental Entomology 10/2009; · 1.31 Impact Factor
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    ABSTRACT: A growing number of ecologists are using molecular gut content assays to qualitatively measure predation. The two most popular gut content assays are immunoassays employing pest-specific monoclonal antibodies (mAb) and polymerase chain reaction (PCR) assays employing pest-specific DNA. Here, we present results from the first study to simultaneously use both methods to identify predators of the glassy winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae). A total of 1,229 arthropod predators, representing 30 taxa, were collected from urban landscapes in central California and assayed first by means of enzyme-linked immunosorbent assay (ELISA) using a GWSS egg-specific mAb and then by PCR using a GWSS-specific DNA marker that amplifies a 197-base pair fragment of its cytochrome oxidase gene (subunit I). The gut content analyses revealed that GWSS remains were present in 15.5% of the predators examined, with 18% of the spiders and 11% of the insect predators testing positive. Common spider predators included members of the Salticidae, Clubionidae, Anyphaenidae, Miturgidae, and Corinnidae families. Common insect predators included lacewings (Neuroptera: Chrysopidae), praying mantis (Mantodea: Mantidae), ants (Hymenoptera: Formicidae), assassin bugs (Hemiptera: Reduviidae), and damsel bugs (Hemiptera: Nabidae). Comparison of the two assays indicated that they were not equally effective at detecting GWSS remains in predator guts. The advantages of combining the attributes of both types of assays to more precisely assess field predation and the pros and cons of each assay for mass-screening predators are discussed.
    Oecologia 01/2008; · 3.01 Impact Factor
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    ABSTRACT: The combined impact of multiple plant parasites on plant performance can either be additive (the total damage equals the sum of the individual effects) or nonadditive (synergistic or antagonistic damage). Two statistical models are available for testing the independent (=additive) effects of two factors. Here we suggest that the natural history of the plant-parasite system should motivate the choice of a statistical model to test for additivity. Using in-field, manipulative experiments, we examined the interactions between the herbivorous mite Calacarus flagelliseta Fletchmann, De Moraes and Barbosa (Acari: Eriophyidae), the fungal pathogen Oidium caricae F. Noack (a powdery mildew), and their host plant Carica papaya L. in Hawaii. First, we found that herbivorous mites had a moderate negative effect on powdery mildew: when mites were absent, powdery mildew colonies were larger and more numerous. Second, we showed that each plant parasite, when evaluated alone, significantly reduced several measures of plant performance. Third, we found that the combined impact of mites and mildew on plant performance is mostly additive and, for a few variables, less than additive. Finally, we explored compensatory responses and found no evidence for nonlinearities in the relationship between plant performance and cumulative parasite impact. Plants are almost universally subject to attack by multiple herbivores and pathogens; thus a deeper understanding of how multiple plant parasites shape each other's population dynamics and plant performance is essential to understanding plant-parasite interactions.
    Ecological Applications 01/2007; 16(6):2382-98. · 3.82 Impact Factor
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    ABSTRACT: The recent invasion of southern California by the glassy-winged sharpshooter (GWSS), Homalodisca coagulata (Say) (Hemiptera: Cicadellidae), has triggered a statewide control effort. Management of GWSS will include biological control using resident and imported natural enemies. Currently, very little information is available on the role of generalist predators in suppression of GWSS eggs, nymphs or adults. We have developed a sharpshooter egg-specific monoclonal antibody (MAb) for use as a diagnostic tool for predator gut content analysis. The MAb was tested by an indirect enzyme-linked immunosorbent assay (ELISA) for specificity to the different life stages of GWSS, smoke-tree sharpshooter (STSS), Homalodisca liturata Ball (Hemiptera: Cicadellidae), and various life stages of 27 other arthropod species. We found that the MAb only reacted to the egg stage of both sharpshooters and, to a lesser extent, to the adult stage of gravid GWSS and STSS females. Moreover, the ELISA was more responsive to younger GWSS eggs than older ones. Laboratory trials were conducted to determine how long GWSS egg antigen remained detectable in the guts of the green lacewing, Chrysoperla carnea Stephens (Neuroptera: Chrysopidae) and the ladybird beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) using both an indirect and sandwich ELISA format. We found that GWSS egg antigen was detectable for up to 30 and 12 h in the guts of C. carnea and H. axyridis; respectively, and that the sandwich ELISA was much more sensitive than the indirect ELISA. Finally, 98 field-collected lacewings were examined for sharpshooter remains using our sharpshooter-specific sandwich ELISA. The assay detected sharpshooter egg antigen in 8.2% of the lacewings examined. This work represents a first step towards identifying the GWSS predator complex.
    Biological Control. 01/2006;
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    ABSTRACT: To aid in identifying key predators of Proconiini sharpshooter species present in California, we developed and tested molecular diagnostic markers for the glassy-winged sharpshooter, Homalodisca coagulata (Say), and smoke-tree sharpshooter, Homalodisca liturata (Ball) (Homoptera: Cicadellidae). Two different types of markers were compared, those targeting single-copy sequence characterized amplified regions (SCAR) and mitochondrial markers targeting the multicopy cytochrome oxidase subunit genes I (COI) and II (COII). A total of six markers were developed, two SCAR and four mitochondrial COI or COII markers. Specificity assays demonstrated that SCAR marker HcF5/HcR7 was H. coagulata specific and HcF6/HcR9 was H. coagulata/H. liturata specific. COI (HcCOI-F/R) and COII (HcCOII-F4/R4) markers were H. coagulata specific, COII (G/S-COII-F/R) marker was H. coagulata/H. liturata specific, and lastly, COII marker (Hl-COII-F/R) was H. liturata specific. Sensitivity assays using genomic DNA showed the COI marker to be the most sensitive marker with a detection limit of 6 pg of DNA. This marker was 66-fold more sensitive than marker Hl-COII-F/R that showed a detection limit of 400 pg of DNA. In addition, the COI marker was 4.2-fold more sensitive than the COII marker. In predator gut assays, the COI and COII markers demonstrated significantly higher detection efficiency than the SCAR markers. Furthermore, the COI marker demonstrated slightly higher detection efficiency over the COII marker. Lastly, we describe the inclusion of an internal control (28S amplification) for predation studies performing predator gut analyses utilizing the polymerase chain reaction (PCR). This control was critical in order to monitor reactions for PCR failures, PCR inhibitors, and for the presence of DNA.
    Entomologia Experimentalis et Applicata 01/2006; · 1.71 Impact Factor
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    ABSTRACT: The market for insuring insect damage is far from complete. This study introduces a new type of derivative instrument-insect derivatives-that provide growers a market-based means of transferring insect risk to speculators or others who may profit from higher insect populations. A risk-neutral valuation model is developed and applied to Bemisia tabaci population data. Economic simulation models show how insect derivatives can improve risk-return results for a representative cotton farm in the Imperial Valley of California. The results suggest that insect derivatives may become important risk management tools for a wide range of growers.
    Agricultural Finance Review 01/2006; 66(May):27-45.
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    ABSTRACT: Invasive insect species cause billions of dollars of direct and indirect damage to U.S. crops each year. The market for insuring insect damage is, however, far from complete. The objective of this study is to design and value insect derivatives, or "bug options," which would offer growers a market-based means for transferring risk of pest damage to speculators or others who may profit from higher insect populations. A bug option valuation model is developed and applied to Bemesia tabaci infestation in cotton. The results show that insect derivatives may become important risk management tools for a wide range of growers.
    02/2005;
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    ABSTRACT: An important element in developing a management strategy for a new pest is the study of its seasonal dynamics and within-plant distribution. Here, we studied the mite Calacarus flagelliseta Fletchmann, De Moraes & Barbosa on papaya, Papaya carica L. (Caricaceae), in Hawaii to quantify 1) patterns of seasonal abundance, 2) its distribution across different vertical strata of the papaya canopy, and 3) shifts in its use of the upper versus the lower surfaces of papaya leaves. Nondestructive sampling conducted in two papaya plantings revealed that 1) populations of C. flagelliseta peak during the summer; 2) mites are most abundant in the middle and lower strata of the plant canopy, and least abundant on the youngest leaves found in the upper canopy; and 3) mites are found more predominantly on the upper leaf surfaces when overall population density peaks, suggesting that individuals move from the lower to the upper leaf surfaces when food resources on the lower leaf surface have been exploited by conspecifics. These results have significant implications for the development of sampling plans for C. flagelliseta in papaya.
    Journal of Economic Entomology 10/2004; 97(5):1563-9. · 1.60 Impact Factor
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    ABSTRACT: Recent work in terrestrial communities has highlighted a new question: what makes a predator act as a consumer of herbivores versus acting as a consumer of other predators? Here we test three predictions from a model (Rosenheim and Corbett in Ecology 84:2538-2548) that links predator foraging behavior with predator ecology: (1) widely foraging predators have the potential to suppress populations of sedentary herbivores; (2) sit and wait predators are unlikely to suppress populations of sedentary herbivores; and (3) sit and wait predators may act as top predators, suppressing populations of widely foraging intermediate predators and thereby releasing sedentary herbivore populations from control. Manipulative field experiments conducted with the arthropod community found on papaya, Carica papaya, provided support for the first two predictions: (1) the widely foraging predatory mite Phytoseiulus macropilis strongly suppressed populations of a sedentary herbivore, the spider mite Tetranychus cinnabarinus, whereas (2) the tangle-web spider Nesticodes rufipes, a classic sit and wait predator, failed to suppress Tetranychus population growth rates. However, our experiments provided no support for the third hypothesis; the sit and wait predator Nesticodes did not disrupt the suppression of Tetranychus populations by Phytoseiulus. This contrasts with an earlier study that demonstrated that Nesticodes can disrupt control of Tetranychus generated by another widely foraging predator, Stethorus siphonulus. Behavioral observations suggested a simple explanation for the differing sensitivity of Phytoseiulus and Stethorus to Nesticodes predation. Phytoseiulus is a much smaller predator than Stethorus, has a lower rate of prey consumption, and thus has a much smaller requirement to forage across the leaf surface for prey, thereby reducing its probability of encountering Nesticodes webs. Small body size may be a general means by which widely foraging intermediate predators can ameliorate their risk of predation by sit and wait top predators. This effect may partially or fully offset the general expectation from size-structured trophic interactions that smaller predators are subject to more intense intraguild predation.
    Oecologia 09/2004; 140(4):577-85. · 3.01 Impact Factor
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    ABSTRACT: We examined the potential of a leaf roller to indirectly influence a community of arthropods. Two mite species are the key herbivores on papaya leaves in Hawaii: a spider mite, Tetranychus cinnabarinus Boisduval, and an eriophyid mite, Calacarus flagelliseta, which induces upward curling of the leaf margin at the end of the summer when populations reach high densities. A survey and three manipulative field experiments demonstrated that (1) leaf rolls induce a consistent shift in the spatial distribution of spider mites and their predators, the coccinellid Stethorus siphonulus Kapur, the predatory mites Phytoseiulus spp., and the tangle-web building spider Nesticodes rufipes Lucas; (2) the overall abundance of spiders increases on leaves with rolls; (3) the specialist predators Stethorus and Phytoseiulus inhabit the rolls in response to their spider mite prey; and (4) the spider inhabits the rolls in response to the architecture of the roll itself. This study shows the importance of indirect effects in structuring a terrestrial community of herbivores.
    Oecologia 06/2003; 135(3):442-50. · 3.01 Impact Factor
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    ABSTRACT: Using glassy-winged sharpshooter (GWSS) egg-specific monoclonal antibody (MAb) and GWSS-specific genetic markers that we previously developed and optimized, the guts of field-collected predators were screened for the presence of GWSS remains. We have examined the guts of over 700 generalist predators and our analyses revealed that frequent predators of the GWSS include spiders, assassin bugs, lacewings and praying mantis.
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    ABSTRACT: Over 1,500 predators were screened for glassy-winged sharpshooter (GWSS) remains using a GWSS egg-specific monoclonal antibody (MAb) and several GWSS-specific genetic markers. Specimens were collected in 2002 and 2003 from a citrus orchard (Riverside, CA) harboring high densities of GWSS. We found that 6.2% of all specimens examined tested positive for GWSS remains. The most frequent predators to test positive included the assassin bug, Zelus renardii (Kolenati) (Hemiptera: Reduviidae) and the spiders Trachelas pacificus Chamberlin and Ivie (Araneae: Corinnidae) and Olios sp. (Araneae: Sparassidae) with 41, 22, and 19% of the specimens testing positive with either ELISA and/or PCR, respectively.
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    ABSTRACT: We just completed the first year of a multi-year research project dedicated to quantifying predation rates on GWSS nymphs and adults and qualifying predation on eggs. There are enough protein/antibody complexes commercially available that each GWSS in a field cage can be marked with a specific protein. We marked two GWSS adults and two GWSS nymphs, each separately with a unique protein and released them into small field cages (N=60) placed in a citrus orchard for 8 hours. Each cage also contained a sentinel GWSS egg mass and an assemblage of six potential GWSS predators. The experiment contained a day and night treatment. Observed mortality for each GWSS life stage and predator species was determined by simply counting the number of survivors remaining in each cage after 8 hours. Results showed that GWSS adults were preyed upon three times more frequently than nymphs and mostly during the day light cycle. Ultimately, the gut contents of each predator will be analyzed by four protein-specific ELISAs to determine how many GWSS each individual predator consumed (note: we are currently conducting these assays). Additionally, the gut contents of each predator will be examined by a GWSS egg-specific sandwich ELISA to determine the frequency of predation on GWSS eggs.
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    ABSTRACT: ABSTRACT A glassy-winged sharpshooter (GWSS) protein marking system is being developed for use as a diagnostic tool for predator gut content analysis. We determined that GWSS can be markedwith 100% efficiency for at least 7 days after feeding on protein-marked plant material or spraying with a topical protein solution. Moreover, feeding trials have shown that protein marked insects can be detected by a protein-specific ELISA in the guts of predators that consumed,them. Field studies are being initiated that will quantify the predation rates of an assemblage of predators on GWSS using a multitude of protein- specific ELISAs.
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    ABSTRACT: A glassy-winged sharpshooter (GWSS) protein marking system is being developed for use as a diagnostic tool for predator gut content analysis. We determined that GWSS can be marked with 100% efficiency for at least 7 days after feeding on protein-marked plant material or spraying with a topical protein solution. Moreover, feeding trials have shown that protein marked insects can be detected by a protein-specific ELISA in the guts of predators that consumed them. Field studies are being initiated that will quantify the predation rates of an assemblage of predators on GWSS using a multitude of protein- specific ELISAs.
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    ABSTRACT: To aid in identifying key predators of Proconiini sharpshooter species present in California, we developed and tested molecular diagnostic markers for the glassy-winged sharpshooter Homalodisca coagulata (Say) and smoke-tree sharpshooter Homalodisca liturata (Ball) (Homoptera: Cicadellidae: Proconiini). Two different types of markers were compared, those targeting single-copy sequence characterized amplified regions (SCAR) and mitochondrial markers targeting the multi-copy cytochrome oxidase subunit genes I (COI) and II (COII). A total of six markers were developed, two SCAR and four mitochondrial COI or COII markers. Specificity assays demonstrated that SCAR marker HcF5/HcR7 was H. coagulata- specific and HcF6/HcR9 was H. coagulata/H. liturata-specific. COI (HcCOI-F/R) and COII (HcCOII-F4/R4) markers were H. coagulata-specific, COII (G/S-COII-F/R) marker was H. coagulata/H. liturata-specific, and lastly, COII marker (Hl- COII-F/R) was H. liturata-specific. Sensitivity assays using genomic DNA showed the COI marker to be the most sensitive marker with a detection limit of 6 pg of DNA. This marker was 66-fold more sensitive than marker Hl-COII-F/R that showed a detection limit of 400 pg of DNA. In addition, the COI marker was 4.2-fold more sensitive than the COII marker. In predator gut assays, the COI and COII markers demonstrated significantly higher detection efficiency than the SCAR markers. Furthermore, the COI marker demonstrated slightly higher detection efficiency over the COII marker. Lastly, we describe the inclusion of an internal control (28S amplification) for predation studies performing predator gut analyses utilizing PCR. This control was critical in order to monitor reactions for PCR failures, PCR inhibitors, and for the presence of DNA.

Publication Stats

123 Citations
17.47 Total Impact Points

Institutions

  • 2003–2009
    • University of California, Davis
      • Department of Entomology
      Davis, CA, United States
  • 2006–2008
    • University of California, Berkeley
      • Department of Environmental Science, Policy, and Management
      Berkeley, California, United States