Non Technical Summary
Recent research has revealed that goldenrod (Solidago altissima) can perceive the pheromones of its co-evolved herbivore and respond by priming its defense response, presumably because the pheromone serves as a reliable cue associated with impending herbivory. Our preliminary data indicate that American cranberry (Vaccinium macrocarpon) can similarly detect and respond to a blend of three sex pheromones being developed for a mating disruption program against three key, co-evolved lepidopteran pest species. Caterpillars that fed upon pheromone-exposed cranberry plants ate less tissue, gained less weight, and suffered greater mortality than caterpillars on control plants. Notably, cranberry plants exposed to the pheromone blend also grew more than unexposed plants, a result also found with S. altissima that suggests some plant species may not exhibit expected ecological tradeoffs between growth and defense. Building on these initial observations, we propose to (i) more fully characterize the influence of pheromone exposure to cranberry on caterpillar herbivory and survival and plant growth; (ii) elucidate key defense mechanisms underlying cranberry's responses to the three caterpillar species following exposure to the pheromones; and (iii) document field-scale effects of pheromone exposure on commercial cranberries. Our proposal aligns well with the priorities of the "Pest and Beneficial Species" program because we will study novel, recently revealed ecological interactions, and their mechanistic underpinnings, in a high-value crop species. Moreover, our research has strong potential to reveal key, basic details of pheromone-induced defense priming and evolution of pheromonal communication systems, while contributing significantly to development of an innovative pest management strategy.
Animal Health Component
Research Effort Categories
Goals / Objectives
Our specific objectives are to:In the lab, fully document the influence of pheromone exposure to cranberry on herbivore performance and growth responses of cranberries (V. macrocarpon). In this objective, we will use a mating disruption-based, three-species lepidopteran pheromone blend and focus on organismal-level outcomes, including insect growth and survival, plant damage and growth, tradeoffs (e.g., growth/defense), and reproductive (fitness) consequences of pheromone-induced priming for cranberry. We will also test blueberry (Vaccinium angustifolium) for similar responses because it is a congener of cranberries, is native to similar habitats in North America, and shares multiple pest species with cranberries.Elucidate key biochemical and molecular mechanisms underlying cranberry's responses to the lepidopteran pheromones. Part of this work will focus on the species-specific effects of pheromone/caterpillar identity on induction of phytohormone-mediated signaling pathways and expression of key defense-related genes.Document field-scale effects of pheromone exposure on cranberry growth as well as performance and survival of sentinel larvae in commercial fields. This work will dovetail with ongoing mating disruption programs, and assess the impacts of chronic pheromone exposure on pest populations, damage from pest species, and plant productivity.
To more fully document the details of this interaction, we will conduct a large-scale factorial experiment in environmental chambers in WI to evaluate (i) success of Sparganothis caterpillars on pheromone-exposed and unexposed V. macrocarpon plants and (ii) growth and productivity of exposed and unexposed V. macrocarpon with and without Sparganothis caterpillar feeding. Methods: As described for our preliminary data, we will plant three cranberry plugs (same genetic background as Exp. #1) in each pot and let them establish for 6 wk. In glass jars (Fig. 3), we will then expose 60 pots to the lepidopteran pheromone blend for 5 d, using slow-release pellets (a newer release method that is easier to use than SPLAT®), while an additional 60 control plants are exposed to pheromone-free, control pellets. This experiment will progress in uniform conditions in balanced batches of plants based on the number of glass jars we have available. As described in our preliminary experiments, we will standardize plant size, then confine 10 Sparganothis neonates (from a WI lab colony) to half of the plants in each exposure treatment for 21 d, resulting in four treatments (N = 30 for each): (i) unexposed/no caterpillars; (ii) unexposed/caterpillars; (iii) exposed/no caterpillars; (iv) exposed/caterpillars. Afterward we will track herbivory and caterpillar development, plant growth and flower and seed production. As V. macrocarpon is an obligate outcrosser, we will introduce two bumble bee hives (Koppert Biological Systems, Inc) to facilitate fruit and seed production (we have used bumble bees with success in previous greenhouse experiments; they perform better than honeybees in such confined spaces).We hypothesize that caterpillar feeding on pheromone-exposed plants induces stronger concentrations of the defense phytohormone jasmonic acid. To test this hypothesis in cranberry, we will analyze biochemical and molecular mechanisms underlying enhanced plant defenses by assessing phytohormone levels and defense gene expression in pheromone-exposed and unexposed plants subject to herbivory. In preparation for these biochemical and molecular analyses, we will collect and freeze plant tissue from our other experiments. In light of our previous work with S. altissima and previous studies with JA in cranberries, we will focus on a suite of defense-related phytohormones, genes in the octadecanoid pathway and others know to be involved in JA-mediated induced defenses, including terpene synthases, which are important anti-herbivore defenses for V. macrocarpon. We will harvest and freeze damaged and undamaged leaves from each treatment at five time points (0, 6, 12, and 24, 48 h) for phytohormone and gene-expression assays. For each timepoint, we will destructively sample in individual pots from randomly selected uprights and harvest eight similar sized leaves (four with equivalent damaged and four undamaged from the same positions along the upright; undamaged leaves on plants with caterpillars will be used to characterize the systemic defensive response of plants); these leaves will be divided equally for phytohormone analysis and gene expression. Levels of phytohormones and gene expression will be compared across timepoints using ANOVA or Student's t-test as appropriate for the design of each experiment.At four large commercial cranberry marshes (= farm) in central WI (where we have ongoing mating disruption trials with treated/untreated blocks), we will embed plots for the pheromone-induced defense/growth experiments. Within each of the four marshes, there will be a single pair of very large blocks: one will be the mating disrupted block and the other, a 'standard grower practice' (no mating disruption) control block. We will apply pheromone using described protocols (Steffan et al. 2017) to provide uniform rates and spatial distributions of the pheromone carriers (a slow-release wax matrix). We will deploy pheromone-baited traps to assess degree of disruption for all three moth species. Embedded within each mating disrupted block and control block at each marsh will be 12 plots (24 total plots per marsh; across the four marshes, 48 plots). In each plot will be a 1×1-m mesh exclusion-cage. Half the cages in any given block (i.e., 6 cages) will be populated with 10 sentinel 2nd instar sparganothis larvae; the other cages in the block (6 cages) will have no larvae added. Thus, within the mating-disruption treatment factor (pheromones present/absent), there will be a nested herbivore treatment, resulting in four treatments (n = 6 each): pheromones/herbivores, pheromones/no herbivores, no pheromone/herbivores, no pheromones/no herbivores. Prior to adding larvae, we will "Dvac" the enclosed cranberry canopy to minimize background arthropod abundance. We will initiate the trial mid- to late-June of yr 2 and 3. Mid- to late June represents the likely period in which sparganothis adults would be flying and ovipositing. The duration of this trial will be weather-dependent since larval growth is temperature-mediated. We will conclude the experiment when larvae in control plots (no pheromones present) begin to reach the 5th instar, which would likely require 10-14 days. Response variables and statistical analyses: We will measure larval survival per cage, mean dry-weight, and developmental status (instar distribution among the surviving larvae). We will count cranberry upright density per square meter, and take subsamples of canopy biomass (dry-weight per 0.25 sq meters). We will analyze plant response metrics via 2-way ANOVA, looking for main and interactive effects between the pheromone and herbivore factors. The insect responses will be analyzed via 1-way ANOVA to assess the effects of the pheromone treatment on the larval metrics.