Project : USDA ARS

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Research Project: Systematics of Acari and Hemiptera: Plant Pests, Predators, and Disease Vectors

Location: Systematic Entomology Laboratory

2024 Annual Report

Objectives
New Objective 1: Conduct integrative systematic research of molecular (including Ag100Pest data) and morphological data to: determine species boundaries; recognize, describe, and illustrate new and invasive species; develop identification keys; hypothesize phylogenetic relationships among the respective groups for the purpose of stabilizing classification and providing predictive relationships of species; and investigate host associations and specificity of Acari (mites), Aphidomorpha (aphids), Membracoidea (leafhoppers and treehoppers), Aleyrodomorpha(whiteflies), Coccomorpha (scale insects), and Heteroptera (true bugs) that are pests of or beneficial to U.S. agriculture. [NP304, C1 PS1A; C2 PS2B; C3 PS3A and 3B] New Objective 2: Develop web-searchable electronic databases, tools, and images of mites, aphids, whiteflies, scale insects (Sternorrhyncha), leafhoppers (Auchenorrhyncha), and true bugs (Heteroptera) in the U.S. National Insect and Mite Collection and obtained through field exploration. This includes developing web-based resources to improve technology transfer of research products and disseminating this information to a broad group of stakeholders (e.g., quarantine, conservation, and biological control personnel). The proposed products will include searchable databases and expert systems of certain mites and hemipteran families. [NP304, C1 PS1A; C2 PS2B; C3 PS3A and 3B] New Objective 3: Provide authoritative identifications of specimens submitted by stakeholders worldwide and manage and curate assigned portions of the U.S. National Insect and Mite Collection, including all taxa in the hemipteran suborders Heteroptera, Auchenorrhyncha, Sternorrhyncha, and Coleorrhyncha, which involve more than one and a half million specimens housed in more than 3,000 insect drawers and mounted on hundreds of thousands of microscope slides, and the Acari with more than 360,000 microscope slide containing over a million specimens. [NP304, C1 PS1A; C2 PS2B; C3 PS3A and 3B]

Approach
Morphological characters will be identified through the examination of specimens using dissecting, DIC, Phase Contrast, CLSM, TT-SEM and Cryo SEM. Use of Cryo-SEM in mite taxonomy is revealing remarkable new character systems that were previously unknown and allowing researchers to re-evaluate poorly understood morphological characters that are difficult, if not impossible, to evaluate based on traditional slide-mounted preparations. This technique not only greatly expands the array of morphological characters available, offering them in greater detail, but it also provides valuable behavioral characters, especially with respect to understanding mite feeding behavior. Cryo-SEM will be used to confirm the intricate details of certain morphological characters visible with light microscopy, especially those of the tarsi and empodia. The novel characters available with Cryo-SEM (e.g., tegument texture and tarsal morphology) will be investigated and assessed using a minimum of 5 species from each genus, or more as time and resources permit. The validity of key characters for separating species and genera will be investigated across the family. TT-SEM and CLSM technologies will be used to further the morphological studies. Although the research will focus primarily on morphological and ecological characters of 4 tetranychid genera and 4 eriophyid genera, these data sets will be augmented with molecular data (COI, 18S, 28S, EF-1') as an exploratory avenue for systematic research in these taxa. We will collaborate with Dr. Ashley Dowling and his team at the University of Arkansas who have expertise in molecular characterization of mites. Character information will include the external and internal morphology of mounted flat mites, adults and immatures, combined with the molecular data and analyzed using TNT and MrBayes. Live specimens used for Cryo-SEM studies will be solicited from colleagues and/or brought into the laboratory from domestic and/or foreign fieldwork following standard quarantine regulations and evaluated for morphological characters. In addition, some slide-mounted specimens will be borrowed from or examined at various institutions worldwide, especially the type specimens located in Canada, Brazil and Australia. More than half of the type specimens located at the National Mite Collection (Beltsville, MD) have been studied under DIC and Phase Contrast microscopy. Additional specimens will be collected from regions that are poorly represented in accessible collections, including Australia, South America, India and China. Methods of preparation and preservation will follow those previously described for slide mounting and Cryo-SEM.

Progress Report
A substantial amount of the groundwork for the isometopine revisionary study has been completed, with habitus images and plates completed for nearly 80 species, about half of which are new to science, the manuscript outline has been completed, the literature has been compiled, and keys to genera and a key to the 11 species of the tribe Diphlebini, including six of which are new to science, were completed. In addition, a paper on the Indian and Sri Lankan Isometopinae, treating nine genera and 17 species, including six species new to science, has been published. Habitus images of 550 morphospecies of Darnini treehoppers have been imaged and 502 of them have been coded for 66 morphological characters in preparation for a phylogenetic study and species descriptions. Borrowed Brazilan material (530 specimens) is partially sorted to morphospecies. A loan of additional material, with an emphasis on the Colombian fauna, was recently acquired and probably contains more new species. The first-ever regional checklists of treehoppers of Nicaragua and Ecuador are being developed, with completion at approximately 95% and 50%, respectively. Amplification has been attempted for all aspidiotine samples; sequencing of nuclear loci is complete, but amplification of mitochondrial loci has proven difficult. Troubleshooting the amplification of mitochondrial loci included sequencing a subset of mitochondrial genomes (using MinION) to improve primer design, but new primers have not improved results. However, substantial progress has been made toward estimating a family-level, fossil-calibrated phylogeny of scale insects. Seventy species have been submitted for low-coverage genomic sequencing and a custom set of UCE baits have been ordered to ultimately compile a UCE dataset for phylogenomic analysis. In lieu of coding a morphological matrix for specimens of Aspidiotinae, efforts have instead focused on building a morphological matrix to complement a UCE-based molecular matrix for family-level phylogenomic analysis. The dataset currently comprises 164 taxa and 175 characters and is approximately 80% complete. Made 257 urgent and 105 prompt/routine identifications of Heteroptera; 143 urgent and 25 prompt/routine identifications of Auchenorrhyncha; 196 urgent and 8 prompt/routine identifications of Sternorryncha; and 550 urgent and 88 prompt/routine identifications of Acari, all as of June 2024.

Accomplishments
1. Systematics of grass-feeding true bugs. Species belonging to the family Blissidae are among the most economically important true bugs in the suborder Heteroptera. Blissids, often called chinch bugs, represent the third largest family in the Lygaeoidea, with 55 genera and more than 430 species known worldwide. Chinch bugs are the only members of this superfamily that feed exclusively on the sap of grasses and other monocots, making them serious pests of pastures, lawns, corn, sorghum, and small grains. Despite their great economic importance, chinch bugs are extremely difficult to identify, and their relationships are poorly known. This recent study, in collaboration with a colleague from the Museu de La Plata, in Buenos Aires, Argentina, provided redescriptions of all 23 Western Hemisphere genera of chinch bugs, including illustrations of each, recognition of three genera new to science, and an identification key to help distinguish them. This information will allow researchers involved in insect control and plant pest quarantine to accurately identify these pests and better understand their relationships.

2. Identified immature stages of New World treehoppers. Except for a few species in the U.S., the immature stages of New World treehopper genera are largely unknown. This paucity hampers identification of potentially invasive pests because port interceptions are often on immatures. Based on a unique USDA-ARS collection the U.S. National Museum of Natural History, built over the last 40 years, these immatures stages can finally be described, with 36 genera completed so far. These results provide insights into the habits and host plants of the described genera and will enable port identifiers to identify a majority of the intercepted treehopper immatures. The new features only present in immatures will be used to enhance phylogenetic studies of treehoppers and the host plant records will be of interest to ecologists.

3. Scale Insect Morphology is Transformed by Close Relationships with Ants. Root mealybugs are a critically understudied group of scale insects that impact agriculture, perhaps more than appreciated due to their subterranean habit. Recent studies have highlighted artificiality in the taxonomic classification of root mealybugs, which further complicates our understanding of their role and connections in agricultural systems. Such taxonomic issues are due, in part, to convergent evolutionary forces influencing their morphology. One source of convergence involves tight-knit ecological relationships with ants. USDA-ARS scientists in Beltsville, Maryland, and collaborators at Towson University quantified features of morphological evolution among root mealybugs that correspond with obligatory ant-association, including certain traits that confound root mealybug classification. This work establishes a foundation for a natural classification of root mealybugs, as well as characteristics of domestication in complex, non-human (ant) agricultural systems. The results build upon our understanding of symbioses and are critical for systematists, evolutionary biologists, and regulatory agencies that work to prevent the spread of invasive species.

4. Plant Feeding Mites in the Super Families Tetranychoidea and Eriophyoidea. Eriophyidae associated with viruses as well analysis of the genus-virus associations and the impact on several species of fruit tree and ornamental were done in collaboration with the National Arboretum, ARS Researchers in Beltsville, Maryland, scientists from Animal Plant Health Inspection Service (APHIS), University of Florida, State Departments of Agriculture of California, Hawaii, Florida, Brazil, Mexico, Peru and Argentina. Such collaborations have been key to discovering and understanding over 40 eriophyoid virus associations. The crucial importance of this work is that the morphology of the plant and mites implies that the eriophyoid’s ability to damage them is the result of coevolution. These findings have shown that the mite-host associations are more pervasive than previously known and with thousands of undescribed species it represents a major challenge. This will affect how plants are grown and traded around the world. The work with scientists in Brazil on Parasitangona mites opened a new venue of unknown vector possibilities for bacteria and viruses that can also affect livestock in the Americas. Because their small size and ability to carry pathogens understanding acari is vital for the planning of future agriculture and quarantine policies.

U.S. DEPARTMENT OF AGRICULTURE

Systematic Entomology Laboratory: Beltsville, MD