Project : USDA ARS

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

Location: Systematic Entomology Laboratory

2021 Annual Report

Objectives
The long-term goal of this project is to produce systematic revisions of monophyletic groups of Acari (mites) that are important to U.S. agriculture and transfer this information to stakeholders, regulatory agencies, scientists, and the general public. The project will focus on two mite families: Tetranychoidea (spider mites and flat mites) and Eriophyioidea (gall, rust and bud mites), which are of increasing importance on crops, ornamentals and fruit trees in the U.S. Other related plant feeding superfamilies, like the white mites (Tarsonemoidea), will continue to be monitored. Many genera in the Eriophyioidea are affecting millions of fruit trees (e.g., citrus, apple, avocado, mango and berries), palms and ornamentals, and several species of Eriophyiod mites are strongly linked with the transmission of plant viruses. To complicate manners, many of the viruses may help the mites to affect the plant. The spider mites (several genera, including Tetranychus, Oligonychus, Eotetranychus and Eutetranychus) are major pest of crops and ornamentals and their roles as invasive species have been increasing, which increases the need for new management alternatives. Despite their economic importance and our limited knowledge, these mite genera need rigorous systematic revision, and the tools available for their identification need improvement. This project plan focuses on the following objectives: Objective 1: Conduct systematics and taxonomic research to revise the superfamilies Tetranychoidea and Eriophyoidea (Acari), and curate and expand the U.S. National Mite Collection in support of this effort. [NP304, C1, PS1A; C2, PS2B; C3, PS3A and 3B; C4, PS4A and 4B]. Objective 2: Expand and enhance web-based information resources for systematic acarology, emphasizing mite-plant-associations and their taxonomy, ecology, biology and geographic distributions. [NP304, C1, PS1A; C2, PS2B; C3, PS3A and 3B; C4 PS4A and 4B].

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
Several genera of mites in the family Tetranychidae (including the Tetranychus and Oligonychus) were acquired and mounted for studies under the differential interference contrast (DIC) microscope as well under the cryo-scanning electron microscope. Three important genera in the family Eriophyidae were mounted and studied. Several genera in the order Acariformes were reviewed and save for further molecular studies. In collaboration with the Smithsonian and University of Florida, a worldwide literature search of plant-feeding mites associated with diseases (fungi and viruses) has been initialized. Made 435 urgent identifications (Digital 383, molecular 1, morphological 51), 8732 “routine, promts and IDA’s ” identifications of ACARI and Orthoptera from 30 May 2020 to 30 May 2021.

Accomplishments
1. Supervisory Research Entomologist. Systematic studies of plant-feeding mites in Tetranychidae and Eriophyiidae and taxonomy studies in related families in the Acariformes were accomplished. Continuous studies on species in the family Eriophyidae associated with viruses are helping to understand the genus-virus associations and the impact on several fruit trees and ornamentals. ARS researchers at Beltsville, Maryland, collaborated with scientists from Animal Plant Health Inspection Service (APHIS), University of Florida, State Departments of Agriculture of California, Hawaii, and Florida, and scientists from Brazil, Mexico, Peru, and Argentina established collaboration on invasive species identification. Several observations and measurements of mites collected in the United States were studied using differential contrast light microscopy, confocal microscopy, table top SEM and low temperature scanning electron microscopy, which allowed the researchers to define characteristic structures and patterns for the correct identification of the mites.

U.S. DEPARTMENT OF AGRICULTURE

Systematic Entomology Laboratory: Beltsville, MD