Location: Chemistry Research2021 Annual Report
Objective 1: Investigate semiochemicals of agricultural plant-insect-microbe interactions, with emphasis on mites, weevils, leaffooted bugs, and fruit flies; and, volatile biomarkers from insect or microbe infestations of agricultural products. Objective 2: Collect, analyze, and identify semiochemicals of pollinator pest-host and nematode-plant-microbe interactions, including varroa mites, hive beetles, entomopathogenic nematodes, or associated soil/root microbes. Objective 3: Survey floral nectar microorganisms occurring in flowering crops and determine their impacts on nectar chemistry, pathogen loads, and pollinator affinity.
Investigate the chemical communications of agricultural plant-insect-microbe systems, such as those involving mites, weevils, leaffooted bugs, and fruit flies, as well as entomopathogenic nematodes and their associated soil/root microbes. This work will also include investigating how pheromones and multitrophic signaling can be utilized for effective control of pest organisms. Provide new or improved biological, behavioral, or cultural control methods to reduce agricultural reliance on broad spectrum chemistries. To address the ever-changing abiotic stressors, will provide flexible pest management tools for agricultural ecosystems, including those that protect plant-pollinator habitats or hosts. Will address these pollinator issues by identifying semiochemicals of pollinator pest-hosts, including varroa mites and hive beetles, and providing cost-effective, environmentally safe pest management strategies. This research will utilize numerous interactive laboratory- and field-based bioassays with insects, mites, microbes, nematodes, and plants, as well as purified biochemicals and other organisms. Isolation and identification of new bioactive chemicals that mediate arthropod and nematode behaviors and other inter-organismal interactions will be achieved using a combination of approaches including HPLC, LC-MS, preparative flash chromatography, GC-MS, FT-IR, NMR, micro-degradation, and synthesis where applicable. Major target insects for this research will include those listed above, with other target insects selected as needed during progression of the project.
Progress has been made on Research Project 6036-22430-001-00D by Gainesville, Florida, ARS Scientists. In Objective 1, progress includes the following: a field technique for volatile collection was developed and tested successfully; a collection filter was strategically placed within a bag covering the plant or part of the plant; and, a standardized time is pulled through the Tenax filter to be analyzed by thermal desorption GC-MS. This resulted in a high throughput of plants and samples within a short time. Volatiles were collected by collaborators of budding blueberry plans, pinpointing volatiles correlated with gall midge attack. Similarly, volatiles were collected from Roseau Cane to determine if volatiles could be correlated with scale insect infestations. ARS researchers in Gainesville, Florida, investigated the maize weevil’s attraction to plants that produce host grains where weevils feed and reproduce. Experiments were conducted to determine if there is a predisposition in orientation to plants dependent upon the grain that was fed upon. To account for all weevils used in the study we included weevils located on the plant, soil, and roots. Results indicated that, of the plants tested, male and female weevils held the highest attraction to the rice plants. There was no bias for host plant dependency upon previous feeding. There were considerably more barley-reared males and females located on the soil surrounding all plants; however, there was no significant difference amongst the weevils for their location on the plant roots. Future research will focus on isolating specific rice plant odors to be used in the development of an attractant for use in a trapping system. The use of the weevil’s sex pheromone in conjunction with a host volatile (food or oviposition) will greatly enhance attraction. This will allow for the development of a novel, inexpensive method for monitoring and control and would help reduce crop loss. In a separate study volatiles from leaffooted bug (LFB)-infested yucca flowers in a Georgia field were collected and analyzed via Gas chromatography–mass spectrometry (GC-MS). Volatile profiles are currently under evaluation to determine individual odor identities. Yucca and tomato plants were also planted in a Florida field site to provide additional candidate sites for LFB infestations. Collected LFB from the Georgia yucca flowers were housed in the Florida laboratory location to assist with determining successful colony conditions. Objective 2, progress included the following: using Steinernema diaprepesi as a model nematode ARS researchers in Gainesville, Florida, established that the nematodes’ host insect preference can be successfully altered by selective rearing. Since ARS researchers earlier established that EPN attraction to volatile organic compounds can be temporarily altered by a priming process we also tested the hierarchical order of host plant preference and learning. ARS researchers established that although entomopathogenic nematodes (EPNs) can be primed to be attracted to normally non-attractive compounds, when given a choice the nematodes prefer volatiles released by the insect they were reared on; infective juveniles of Heterorhabditis bacteriophora, S. riobrave, and S. diaprepesi were used to study host selectivity and strength of a potential recruitment pheromone. We prepared crude active pheromone extracts for all nematodes and found that their specificity could be correlated with nematode foraging behavior. Using fractions from liquid chromatography we found that all the nematodes used different pheromone blends, but also noted substantial overlap. The pheromone for S. diaprepesi has been partially isolated and will be identified; investigated small hive beetle (SHB) attraction using ripe fruit and a fruit-based attractant containing ethanol, ethyl butyrate, acetic acid, ethyl acetate and acetaldehyde. A laboratory trapping assay was performed using ripe fruit and the fruit-semiochemical attractant blend. Results indicated that the synthetic fruit blends captured beetles at the same rate as the cut fruit. The blend with the highest concentration had significantly more beetles captured. The isolated fruit volatiles show promise as a possible attractant for control and monitoring of SHB; and, in collaboration with researchers at the University of Florida, ARS researchers in Gainesville, Florida, investigated the carbon dioxide respiration of all stages of honey bee drones and workers (collectively called castes). An experiment was conducted using equipment designed to measure plant leaf-level gas exchange, which allowed us to measure the respiration rate of the honey bee castes. Results indicated significant differences in carbon dioxide respiration levels of adult worker and drone honey bees. The comparison of worker and drone pupae showed no difference in the respiration levels; however, there was a considerable difference in respiration levels of the worker and drone larvae. This research provided critical information on the respiration levels of honey bee castes and how Varroa may select drone larvae for reproduction. This knowledge is a crucial step for the advancement in research studies and the development of management protocols for Varroa. Objective 3 progress included successful collection and preservation of microbes from blueberry flowers. These microbes will be screened for their ability to fight and prevent diseases that infect crop flowers. Nectar was collected from different blueberry cultivars grown in organic and conventional farms. A blueberry species native to Florida growing wild in nature preserves was also included. From these flowers, scientists in Gainesville, Florida, have isolated and identified ca. 100 unique nectar microbes. Several of these microbes have never been reported before and may be new species discoveries. Currently, ARS researchers in Gainesville, Florida, are preparing a paper to report how species, cultivar, and management practices (wild, organic, and conventional) impact the type and number of microbes dwelling in blueberry nectar.
1. Discovered pepper weevil oviposition marking pheromone. The pepper weevil is a serious insect pest of peppers with larvae feeding internally on portions of the fruit and the adults feeding externally on fruit and leaf buds. Notwithstanding chemical measures, weevils are hard to control, creating the need for effective control measures. After depositing an egg within the pepper female weevils mark the oviposition site, thus inhibiting further oviposition in that pepper. In collaboration with University of Florida, ARS scientists from Gainesville, Florida, isolated the pheromone components and found it to be comprised of volatile as well as contact acting components. The published results are expected to provide the foundation for a biological control program as well as serving as a guide to isolation of similar pheromones from other Anthonomus pest weevil species.
2. Solventless techniques for collection of volatile semiochemicals. Volatile collections and chemical identifications are commonly used in chemical ecological research with solventless sampling techniques becoming popular due to their ease of use and lack of solvent interfering with compound detection. However, there are also drawbacks with the techniques. ARS scientists form Gainesville, Florida, demonstrated how thermal degradation, an often-neglected problem, can be avoided by carefully designed procedures. In an additional investigation we studied pros and cons of several solventless and solvent-based control methods and highlighted several potentially serious problems. Based on these discoveries we developed unique guidelines that provide fundamental assistance with choosing suitable techniques for laboratory and field samplings.
3. Use of entomopathogenic nematodes (EPNs) in biological control. EPNs are promising control agents for control of soil dwelling insects, and to some extent also for control of pest insects above ground. Scientists at ARS in Gainesville, Florida, in collaboration with other ARS and University laboratories discovered how EPNs utilize damage induced root volatiles to find their host insects. ARS scientists in Gainesville, Florida, have now discovered that some of these damage induced root volatiles also affect the insect’s ability to defend itself, leading to increased mortality of the invading nematodes. This discovery will be of help when choosing nematode attractants that can be used in an agricultural setting and furthermore will explain field observations.
4. Honey bee caste respiration. Varroa mites are a devastating honey bee pest that transmit numerous viruses while feeding on bee larvae, pupae, and adults causing bee deformity and eventually killing the hive. Honey bee pollination contributes to increased yields and superior quality crops and accounts for nearly $20 billion added value to U.S. crop production annually. Due to pesticide resistance and honey bee exposure to pesticides, new and improved control measures are needed to combat Varroa mites. ARS researchers in Gainesville, Florida, in collaboration with researchers at the University of Florida have investigated the carbon dioxide respiration of all stages of honey bee drones and workers. Research performed on honey bees indicated a significant difference in the carbon dioxide levels of adult worker and drone honey bees. There was a noticeable difference in respiration levels of the worker and drone larvae. Drone larvae are the preferred host stage for Varroa reproduction. This research provides critical information on the respiration levels of honey bee castes and how Varroa may select drone larvae for reproduction. This research is a vital for the advancement in the development of management protocols for Varroa.
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Rering, C.C.; Rudolph, A.B.; Beck, J.J. Pollen and yeast change nectar aroma and nutritional content alone and together, but honey bee foraging reflects only the avoidance of yeast. Environ. Microbiol. 2021, https://doi.org/10.1111/1462-2920.15528.
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Christensen, S.A.; Santana, E.; Alborn, H.T.; Block, A.K.; Chamberlain, C.A. 2021. Metabolomics by UHPLC-HRMS reveals the impact of heat stress on pathogen-elicited immunity in Maize. Metabolomics. 17:6. https://doi.org/10.1007/s11306-020-01739-2.
Addesso, K.M.; Alborn, H.T.; Bruton, R.G.; Mcauslane, H.J. 2021. A multicomponent marking phermone produced by the PEPPER WEEVIL, Anthonomus eugeni (Coleoptera: Curculionidae). Chemoecology 31:247-258. 2021. https://doi.org/10.1007/s00049-021-00347-3.
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