Research Update: Asiatic Garden Beetle Population Genetics

March 3, 2021

Tilmon Lab graduate student Adrian Pekarcik received a USDA AFRI EWD Predoctoral Fellowship to investigate the Asiatic garden beetle (AGB), Maladera castanea, an annual white grub species that was introduced to the U.S. in 1921 and has spread to at least 25 states and 2 Canadian provinces. Historically it was a pest of turfgrasses and ornamentals, however, in the last 10 years AGB has emerged as a new pest of field corn in Indiana, Michigan and Ohio. Grub feeding on seedling roots in the spring causes plants to stunt, wilt, discolor and die. High grub densities result in extensive plant stand losses exceeding 40%. Interestingly, AGB populations have only recently infested field crops and only in the Great Lakes region in spite of their broad distribution and long history in the U.S. These infestations are localized in sandy soils characteristic of this tri-state region. We hypothesize that these beetles comprise a genetically distinct population and propose to use molecular genetic tools to compare genetic structure among North America AGB populations. This serves the longer-term goal to understand why AGB has emerged as a new pest. Our objectives are to (1) develop molecular markers for AGB, and (2) assess North American populations for habitat-specific variation and/or geographic variation. We propose a novel approach that utilizes specific-locus amplified fragments sequencing (SLAF-seq) to identify single nucleotide polymorphisms (SNPs) for AGB. This project fits within the USDA AFRI Education and Workforce Development Program Area of Plant Health and Production and Plant Products as host associated genotypes could help us predict populations at-risk of future infestations. Additionally, these tools will allow for future investigations into AGB.

AGB beetle populations have been sampled from 10 states in 2020, and additional states will be collected from in coordination with collaborators this year! Efforts have screened restriction enzymes for fragment size distribution and frequency (the more evenly distributed the fragments, the better!). Preliminary work screened the restriction enzymes MseI and NlaIII on our Ohio and New Jersey AGB populations. In coordination with Dr. Michael Sovic (OSU Center for Applied Plant Sciences) through a CAPS opportunity grant and Ohio Supercomputer Center resource unit grant, we used AftrRAD software to identify SNPs from the sequencing runs. Although the program was succesfully run with our samples, this particular combination of restriction enzymes yielded only several SNPs instead of thousands. Additional pairs of enzymes were evaluated via in silico (i.e. computer simulations) digestions using the genomes of three other beetle species; AseI and EcoRI will be used for our second attempt at SLAF-sequencing and SNP detection in AGB populations.

Stay tuned for updates related to Adrian's USDA predoctoral fellowship research!