Pre- and postsynaptic nanostructures increase in size and complexity after induction of long-term potentiation.

Synapses, specialized contact sites between neurons, are the fundamental elements of neuronal information transfer. Synaptic plasticity involves changes in synaptic morphology and the number of neurotransmitter receptors, and is thought to underlie learning and memory. However, it is not clear how these structural and functional changes are connected. We utilized time-lapse super-resolution STED microscopy of organotypic hippocampal brain slices and cultured neurons to visualize structural changes of the synaptic nano-organization of the postsynaptic scaffolding protein PSD95, the presynaptic scaffolding protein Bassoon, and the GluA2 subunit of AMPA receptors by chemically induced long-term potentiation (cLTP) at the level of single synapses. We found that the nano-organization of all three proteins increased in complexity and size after cLTP induction. The increase was largely synchronous, peaking at ∼60 min after stimulation. Therefore, both the size and complexity of individual pre- and post-synaptic nanostructures serve as substrates for tuning and determining synaptic strength.

Characterizing the blood-brain barrier and gut barrier with super-resolution imaging: opportunities and challenges.

Brain and gut barriers have been receiving increasing attention in health and diseases including in psychiatry. Recent studies have highlighted changes in the blood-brain barrier and gut barrier structural properties, notably a loss of tight junctions, leading to hyperpermeability, passage of inflammatory mediators, stress vulnerability, and the development of depressive behaviors. To decipher the cellular processes actively contributing to brain and gut barrier function in health and disease, scientists can take advantage of neurophotonic tools and recent advances in super-resolution microscopy techniques to complement traditional imaging approaches like confocal and electron microscopy. Here, we summarize the challenges, pros, and cons of these innovative approaches, hoping that a growing number of scientists will integrate them in their study design exploring barrier-related properties and mechanisms.

Control of Phytonemus pallidus (Acari: Tarsonemidae) from strawberry transplants using controlled atmosphere temperature treatment.

Since it inhabits young leaves and buds of strawberry (Fragaria × ananassa Duchesne) crowns, cyclamen mite (Phytonemus pallidus Banks) is a difficult pest to control with biological or chemical means once it is present in a field. Controlled atmosphere temperature treatment (CATT) is a successful technique that has been commercially used in the Netherlands for nearly 2 decades to disinfect strawberry nursery stock, including elimination of cyclamen mite. During CATT, plants are treated at 35 °C, 50% CO2, and 10% O2 under high relative humidity for 48 h. The objective of this study was to test CATT against P. pallidus in North America at a scale that can be easily used on-farms by strawberry growers. Two greenhouse experiments were conducted where infested trayplants were treated with CATT or the acaricide abamectin, and P. pallidus number were compared to control plants. Plants were destructively sampled after 4 weeks, and CATT reduced mobile forms of P. pallidus by 99.9% in both experiments. Abamectin used in the first experiment had an efficacy of 95.5%. Our findings suggest that CATT is effective at nearly eliminating P. pallidus from strawberry planting material, and its application could reduce risks of field infestations and the need for multiple acaricide applications. While our results are encouraging, additional research is needed to assess the effects of CATT on strawberry plant survival, growth, and fruit production.

Host Range and Phenology of Sugarcane Aphid (Hemiptera: Aphididae) and Natural Enemy Community in Sorghum in Haiti.

To determine the factors leading to outbreaks of the sugarcane aphid, Melanaphis sacchari, (Zehntner) (Hemiptera: Aphididae) in sorghum in Haiti, a survey was carried out on farms during two cropping seasons, spring and fall of 2018. A total of 45 plots in three Haitian regions were monitored from the five-leaf stage to grain ripening. Infestation with M. sacchari was significantly higher in spring than in fall, except in one location. Melanaphis sacchari populations varied significantly according to phenological stages of sorghum, with significantly higher abundance during the heading and flowering stages than other stages. In and around sorghum fields, the sugarcane aphid was observed on plants from three families: Poaceae, Malvaceae, and Cucurbitaceae. Aphid natural enemies found in sorghum fields consisted of eight species of ladybeetles (Coleoptera: Coccinellidae), one hoverfly (Diptera: Syrphidae), one lacewing (Neuroptera: Chrysopidae), and one predatory midge (Diptera: Cecidomyiidae). In addition to these predators, two parasitoid species, Adialytus sp. (Hymenoptera: Braconidae) and Pachyneuron aphidis (Bouché) (Hymenoptera: Pteromalidae), emerged from sugarcane aphid mummies. Predator and parasitoid densities were highly affected by growing season, with most of the biological control happening in fall. This study provides insights on sugarcane aphid management in Haiti and the Caribbean Islands.

Multi-label in vivo STED microscopy by parallelized switching of reversibly switchable fluorescent proteins.

Despite the tremendous success of super-resolution microscopy, multi-color in vivo applications are still rare. Here we present live-cell multi-label STED microscopy in vivo and in vitro by combining spectrally separated excitation and detection with temporal sequential imaging of reversibly switchable fluorescent proteins (RSFPs). Triple-label STED microscopy resolves pre- and postsynaptic nano-organizations in vivo in mouse visual cortex employing EGFP, Citrine, and the RSFP rsEGP2. Combining the positive and negative switching RSFPs Padron and Dronpa-M159T enables dual-label STED microscopy. All labels are recorded quasi-simultaneously by parallelized on- and off-switching of the RSFPs within the fast-scanning axis. Depletion is performed by a single STED beam so that all channels automatically co-align. Such an addition of a second or third marker merely requires a switching laser, minimizing setup complexity. Our technique enhances in vivo STED microscopy, making it a powerful tool for studying multiple synaptic nano-organizations or the tripartite synapse in vivo.

Landscape Enhancements in Apple Orchards: Higher Bumble Bee Queen Species Richness, but No Effect on Apple Quality.

Bumble bees are among the most effective pollinators in orchards during the blooming period, yet they are often threatened by the high levels of pesticide use in apple production. This study aimed to evaluate the influence of landscape enhancements (e.g., hedgerows, flower strips) on bumble bee queens in apple orchards. Bumble bee queens from 12 orchards in southern Québec (Canada) were marked, released, and recaptured in the springs and falls of 2017 to 2019. Half of the 12 orchards had landscape enhancements. Apples were harvested in 2018 and 2019 to compare their quality (weight, diameter, sugar level, and seed number) in sites with and without landscape enhancements. Species richness, as well as the occurrence of three species out of eight, was higher in orchards with landscape enhancements than in orchards without such structures. The occurrence of Bombus ternarius was lower in orchards with high levels of pesticide use. Apples had fewer seeds when collected in orchards with landscape enhancements and were heavier in orchards that used more pesticides. Our work provides additional evidence that landscape enhancements improve bumble bee presence in apple orchards and should therefore be considered as a means to enhance pollination within farms.

Supplying honey bees with waterers: a precautionary measure to reduce exposure to pesticides.

Water is essential for honey bees (Apis mellifera L.), but contaminated sources of water in agricultural environments represent a risk of exposure to potentially harmful contaminants. Providing clean water to honey bees could be an efficient and cost-effective measure for beekeepers to reduce bee mortality associated with pesticides and improve the health of their colonies. The main goal of this study was to design a waterer prototype to fulfill the water requirements of honey bees and to evaluate the potential of this waterer in improving colonies' health in agricultural settings, through mitigating the possible impact of an exposure to pesticides from puddle water. We tested the preference of honey bees regarding water composition and waterer prototypes, among which honey bees showed a strong preference for salted water and a poultry-type waterer. Our waterer models were quickly adopted and intensively used through the season in both the context of honey production in field crops and pollination services in cranberry crops. However, in neither context did the use of waterers reduce worker mortality nor increase overall colony weight. Our waterers provided bees with water containing fewer pesticides and were associated with reduced risks of drowning compared to natural sources of water. Our study suggests that the use of waterers fulfills an important requirement for honey bees and represents an interesting and convenient precautionary measure for beekeepers.

Landscape composition and local floral resources influence foraging behavior but not the size of Bombus impatiens Cresson (Hymenoptera: Apidae) workers.

Bumble bee communities are strongly disrupted worldwide through the population decline of many species; a phenomenon that has been generally attributed to landscape modification, pesticide use, pathogens, and climate change. The mechanisms by which these causes act on bumble bee colonies are, however, likely to be complex and to involve many levels of organization spanning from the community down to the least understood individual level. Here, we assessed how the morphology, weight and foraging behavior of individual workers are affected by their surrounding landscape. We hypothesized that colonies established in landscapes showing high cover of intensive crops and low cover of flowering crops, as well as low amounts of local floral resources, would produce smaller workers, which would perform fewer foraging trips and collect pollen loads less constant in species composition. We tested these predictions with 80 colonies of commercially reared Bombus impatiens Cresson placed in 20 landscapes spanning a gradient of agricultural intensification in southern Québec, Canada. We estimated weekly rate at which workers entered and exited colonies and captured eight workers per colony over a period of 14 weeks during the spring and summer of 2016. Captured workers had their wing, thorax, head, tibia, and dry weight measured, as well as their pollen load extracted and identified to the lowest possible taxonomic level. We did not detect any effect of landscape habitat composition on worker morphology or body weight, but found that foraging activity decreased with intensive crops. Moreover, higher diversity of local floral resources led to lower pollen constancy in intensively cultivated landscapes. Finally, we found a negative correlation between the size of workers and the diversity of their pollen load. Our results provide additional evidence that conservation actions regarding pollinators in arable landscapes should be made at the landscape rather than at the farm level.

The impact of lowbush blueberry (Vaccinium angustifolium Ait.) and cranberry (Vaccinium macrocarpon Ait.) pollination on honey bee (Apis mellifera L.) colony health status.

Commercial lowbush blueberry (Vaccinium angustifolium Ait.) and cranberry (Vaccinium macrocarpon Ait.) crops benefit from the presence of honey bee (Apis mellifera L.) for pollination. Unfortunately, beekeepers are observing negative impacts of pollination services on honey bee colonies. In this study, we investigated three beekeeping management strategies (MS) and measured their impact on honey bee colony health and development. Experimental groups (five colonies/MS) were: A) Control farmland honey producing MS (control MS); B) Blueberry pollination MS (blueberry MS); C) Cranberry pollination MS (cranberry MS) and D) Double pollination MS, blueberry followed by cranberry (double MS). Our goals were to 1) compare floral abundance and attractiveness of foraging areas to honey bees between apiaries using a Geographic Information System, and 2) compare honey bee colony health status and population development between MS during a complete beekeeping season. Our results show significantly lower floral abundance and honey bee attractiveness of foraging areas during cranberry pollination compared to the other environments. The blueberry pollination site seemed to significantly reduce brood population in the colonies who provided those services (blueberry MS and double MS). The cranberry pollination site seemed to significantly reduce colony weight gain (cranberry MS and double MS) and induce a significantly higher winter mortality rate (cranberry MS). We also measured significantly higher levels of Black queen cell virus and Sacbrood virus in the MS providing cranberry pollination (cranberry MS and double MS).

Evaluation of Various Sources of Viral Infection in Strawberry Fields of Quebec, Canada.

The decline of cultivated strawberry (Fragaria × ananassa Duchesne ex Rozier; Rosaceae) observed in the province of Quebec, Canada, between 2012 and 2014 was mostly caused by persistent viruses: strawberry mild yellow edge virus (SMYEV) (Potexvirus; Alphaflexiviridae) and strawberry crinkle virus (SCV) (Cytorhabdovirus; Rhabdoviridae); and semi-persistent viruses: strawberry mottle virus (SmoV) (Secoviridae), strawberry vein banding virus (SVBV) (Caulimovirus; Caulimoviridae), and strawberry pallidosis virus (SPaV) (Crinivirus: Closteroviridae) transmitted by insect vectors. The objective of this study was to determine the sources of viral contamination in commercial strawberry fields in Quebec. Specifically, we wished to 1) determine the prevalence of persistent viruses in winged strawberry aphid Chaetosiphon fragaefolii (Cockerell) (Hemiptera: Aphididae) specimens captured; 2) determine the prevalence of all viruses in wild strawberry Fragaria virginiana Miller plants near commercial plantings; and 3) evaluate the viral contamination of strawberry transplants obtained from nurseries and tested before and after planting in commercial strawberry fields. Results indicated high percentage (38%) of the aphids (n = 205) and high percentage (67%) of F. virginiana patches (n = 12) were infected by strawberry viruses. Ultimately, our results showed a low percentage (5%) of the plants from various nurseries (n = 56) were infected before planting, whereas a third (29%) of the healthy exposed plants in the fields (n = 96) became rapidly infected by insect vectors within a year of having been planted. This study provides significant insights on the relative importance of the various sources of contamination in Quebec strawberry fields: C. fragaefolii versus F. virginiana versus nurseries versus post-nursery infections through exposure to virus-carrying insects.

Ability of Muscidifurax raptorellus and Other Parasitoids and Predators to Control Drosophila suzukii Populations in Raspberries in the Laboratory.

Drosophila suzukii is an invasive pest and economic threat to berry crops in Europe and the Americas. Current methods of control of this pest rely primarily on frequent applications of insecticides; therefore, there is a need for alternative control methods to reduce insecticide reliance. In this study, we evaluated the biological control potential of three parasitoid wasps: Diglyphus isaea, Muscidifurax raptorellus and Pachycrepoideus vindemmiae, and four predators: Chrysoperla carnea, Dicyphus hesperus, Orius insidiosus and Podisus maculiventris. Experiments were conducted for 15 days under controlled conditions in experimental arenas with D. suzukii females and raspberries, allowing for all life stages of D. suzukii to be available to natural enemies. Results showed the first evidence of M. raptorellus's ability to parasitize D. suzukii, resulting in a 40% reduction. Orius insidiosus, P. vindemmiae and C. carnea were also efficient, reducing D. suzukii numbers by 49%, 43% and 32%, respectively. Predator preferences for each D. suzukii life stage were assessed. The clutch size, sex ratio and adult size variability of D. suzukii pupal parasitoids were also evaluated. This study expands the list of species that can effectively parasitize D. suzukii and provides new insights into the biological responses of M. raptorellus to D. suzukii pupae.

The Use of the Predatory Mite Stratiolaelaps scimitus (Mesostigmata: Laelapidae) to Control Varroa destructor (Mesostigmata: Varroidae) in Honey Bee Colonies in Early and Late Fall.

The ectoparasitic mite Varroa destructor Anderson & Trueman is a major pest of the honey bee Apis mellifera L. (Hymenoptera: Apidae) and its control is one of the most important challenges that beekeepers have to face. In this study, we investigated the use of the predatory mite Stratiolaelaps scimitus (Womersley) for the biological control of varroa mites in Eastern Canada, as part of an integrated pest management strategy. Our study aimed to evaluate the effectiveness of S. scimitus in controlling varroa populations in early and late fall in comparison with untreated colonies and two currently used organic treatments: Thymovar and oxalic acid. Performing weekly mite drop monitoring, we first compared the effectiveness of two introduction rates of S. scimitus (≈6,250 or 12,500 mites/colony) during a fall treatment (September) and, as we detected no differences of effectiveness between these two treatment types, we used the dosage currently recommended by biocontrol suppliers (≈6,250 mites) in a complementary treatment test (November). Results showed that S. scimitus did not succeed in controlling varroa populations in honey bee colonies when introduced either in early or in late fall according to current suppliers' recommended rates and application method. On the other hand, our results demonstrated that Thymovar and oxalic acid remain effective options for controlling varroa mite populations during fall in Quebec, Canada.

Risk assessment and predation potential of Stratiolaelaps scimitus (Acari: Laelapidae) to control Varroa destructor (Acari: Varroidae) in honey bees.

The biocontrol of the honey bee ectoparasite Varroa destructor is an underexploited but promising avenue that would benefit from being integrated in a Varroa management program. Our study aimed to investigate the potential of the predatory mite Stratiolaelaps scimitus to control Varroa infestations in honey bees. Tests on safety and predation were carried out to: (1) assess the risk of predation of the honey bee brood by S. scimitus under laboratory conditions and within the colony, and (2) evaluate the predation potential of S. scimitus on phoretic Varroa mites. Under laboratory conditions, S. scimitus was able to feed upon free Varroa mites, but also attacked every unprotected honey bee brood stages with a strong preference for bee eggs. When introduced inside colonies, however, S. scimitus does not have negative effects on the survival of the bee brood. Moreover, observations made in the laboratory revealed that S. scimitus does not attack Varroa mites when they are attached to the body of bees. However, all Varroa mites that had naturally fallen from the bees were predated upon by S. scimitus and died in less than 24h. This study provides evidence that S. scimitus does not represent a significant threat to the bee brood, but also suggests that its effect in Varroa control will probably be limited as it does not attack phoretic Varroa mites. Our results represent a first step in assessing the potential of S. scimitus to control V. destructor and provide novel information about the predator's behavior inside the honey bee colony.

Assessing Wild Bee Biodiversity in Cranberry Agroenvironments: Influence of Natural Habitats.

The conservation of bee populations for pollination in agricultural landscapes has attracted a lot of recent research interest, especially for crop industries undergoing expansion to meet increased production demands. In Canada, much growth has been occurring with commercial cranberry production, a field crop which is largely dependent on bee pollination. Wild bee pollinators could be negatively impacted by losses of natural habitat surrounding cranberry fields to accommodate increased production, but growers have little insight on how to manage their lands to maximize the presence of wild bees. Here, we described a 2-yr study where bee diversity and species composition were investigated to better understand the dynamic between natural habitat and cranberry fields. Bees were sampled using pan-traps and hand netting both within cranberry fields and in one of the three adjacent natural habitat types once a week during the crop flowering period. We found that bee community composition among cranberry fields did not differ based on the respective adjacent habitat type, but fields bordered by meadows were marginally less diverse than fields bordered by forest. As one would expect, field and natural habitat communities differed in terms of species composition and species richness. There was no evidence that one type of natural habitat was more favorable for the bees than another. Future agrobiodiversity studies should simultaneously examine bee diversity comprised in both crop fields and adjacent natural environments to better understand the species dynamics essential to the preservation of pollination services.

Planting of neonicotinoid-coated corn raises honey bee mortality and sets back colony development.

Worldwide occurrences of honey bee colony losses have raised concerns about bee health and the sustainability of pollination-dependent crops. While multiple causal factors have been identified, seed coating with insecticides of the neonicotinoid family has been the focus of much discussion and research. Nonetheless, few studies have investigated the impacts of these insecticides under field conditions or in commercial beekeeping operations. Given that corn-seed coating constitutes the largest single use of neonicotinoid, our study compared honey bee mortality from commercial apiaries located in two different agricultural settings, i.e. corn-dominated areas and corn-free environments, during the corn planting season. Data was collected in 2012 and 2013 from 26 bee yards. Dead honey bees from five hives in each apiary were counted and collected, and samples were analyzed using a multi-residue LC-MS/MS method. Long-term effects on colony development were simulated based on a honey bee population dynamic model. Mortality survey showed that colonies located in a corn-dominated area had daily mortality counts 3.51 times those of colonies from corn crop-free sites. Chemical analyses revealed that honey bees were exposed to various agricultural pesticides during the corn planting season, but were primarily subjected to neonicotinoid compounds (54% of analysed samples contained clothianidin, and 31% contained both clothianidin and thiamethoxam). Performance development simulations performed on hive populations' show that increased mortality during the corn planting season sets back colony development and bears contributions to collapse risk but, most of all, reduces the effectiveness and value of colonies for pollination services. Our results also have implications for the numerous large-scale and worldwide-cultivated crops that currently rely on pre-emptive use of neonicotinoid seed treatments.

Taxonomic and functional trait diversity of wild bees in different urban settings.

Urbanization is one of the major anthropogenic processes contributing to local habitat loss and extirpation of numerous species, including wild bees, the most widespread pollinators. Little is known about the mechanisms through which urbanization impacts wild bee communities, or the types of urban green spaces that best promote their conservation in cities. The main objective of this study was to describe and compare wild bee community diversity, structure, and dynamics in two Canadian cities, Montreal and Quebec City. A second objective was to compare functional trait diversity among three habitat types (cemeteries, community gardens and urban parks) within each city. Bees were collected using pan traps and netting on the same 46 sites, multiple times, over the active season in 2012 and 2013. A total of 32,237 specimens were identified, representing 200 species and 6 families, including two new continental records, Hylaeus communis Nylander (1852) and Anthidium florentinum (Fabricius, 1775). Despite high community evenness, we found significant abundance of diverse species, including exotic ones. Spatio-temporal analysis showed higher stability in the most urbanized city (Montreal) but low nestedness of species assemblages among the three urban habitats in both cities. Our study demonstrates that cities are home to diverse communities of wild bees, but in turn affect bee community structure and dynamics. We also found that community gardens harbour high levels of functional trait diversity. Urban agriculture therefore contributes substantially to the provision of functionally diverse bee communities and possibly to urban pollination services.

Increased Acetylcholinesterase Expression in Bumble Bees During Neonicotinoid-Coated Corn Sowing.

While honey bee exposure to systemic insecticides has received much attention, impacts on wild pollinators have not been as widely studied. Neonicotinoids have been shown to increase acetylcholinesterase (AChE) activity in honey bees at sublethal doses. High AChE levels may therefore act as a biomarker of exposure to neonicotinoids. This two-year study focused on establishing whether bumble bees living and foraging in agricultural areas using neonicotinoid crop protection show early biochemical signs of intoxication. Bumble bee colonies (Bombus impatiens) were placed in two different agricultural cropping areas: 1) control (≥ 3 km from fields planted with neonicotinoid-treated seeds) or 2) exposed (within 500 m of fields planted with neonicotinoid-treated seeds), and maintained for the duration of corn sowing. As determined by Real Time qPCR, AChE mRNA expression was initially significantly higher in bumble bees from exposed sites, then decreased throughout the planting season to reach a similar endpoint to that of bumble bees from control sites. These findings suggest that exposure to neonicotinoid seed coating particles during the planting season can alter bumble bee neuronal activity. To our knowledge, this is the first study to report in situ that bumble bees living in agricultural areas exhibit signs of neonicotinoid intoxication.

Neonicotinoid-contaminated puddles of water represent a risk of intoxication for honey bees.

In recent years, populations of honey bees and other pollinators have been reported to be in decline worldwide. A number of stressors have been identified as potential contributing factors, including the extensive prophylactic use of neonicotinoid insecticides, which are highly toxic to bees, in agriculture. While multiple routes of exposure to these systemic insecticides have been documented for honey bees, contamination from puddle water has not been investigated. In this study, we used a multi-residue method based on LC-MS/MS to analyze samples of puddle water taken in the field during the planting of treated corn and one month later. If honey bees were to collect and drink water from these puddles, our results showed that they would be exposed to various agricultural pesticides. All water samples collected from corn fields were contaminated with at least one neonicotinoid compound, although most contained more than one systemic insecticide. Concentrations of neonicotinoids were higher in early spring, indicating that emission and drifting of contaminated dust during sowing raises contamination levels of puddles. Although the overall average acute risk of drinking water from puddles was relatively low, concentrations of neonicotinoids ranged from 0.01 to 63 µg/L and were sufficient to potentially elicit a wide array of sublethal effects in individuals and colony alike. Our results also suggest that risk assessment of honey bee water resources underestimates the foragers' exposure and consequently miscalculates the risk. In fact, our data shows that honey bees and native pollinators are facing unprecedented cumulative exposure to these insecticides from combined residues in pollen, nectar and water. These findings not only document the impact of this route of exposure for honey bees, they also have implications for the cultivation of a wide variety of crops for which the extensive use of neonicotinoids is currently promoted.

Identifying the predator complex of Homalodisca vitripennis (Hemiptera: Cicadellidae): a comparative study of the efficacy of an ELISA and PCR gut content assay.

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.

Multiple plant exploiters on a shared host: testing for nonadditive effects on plant performance.

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.