Demonstration and quantification of restricted mating between fall armyworm host strains in field collections by SNP comparisons

Authors: Nagoshi, Rodney; FLEISCHER, SHELBY - PENNSYLVANIA STATE UNIVERSITY; Meagher, Robert - Rob

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/18/2017
Publication Date: 12/5/2017
Citation: Nagoshi, R.N., Fleischer, S., Meagher Jr, R.L. 2017. Demonstration and quantification of restricted mating between fall armyworm host strains in field collections by SNP comparisons. Environmental Entomology. 110(6):2568-2575.
DOI: https://doi.org/10.1093/jee/tox229

Interpretive Summary: Introduction or invasion by foreign pest insects alone poses a continuing threat to agriculture. Spread of an invasive species can also lead to reproductive hybridization with native species resulting in new phenotypes with additional deleterious economic and environmental consequences. Similarly, acquired deleterious traits (i.e., pesticide resistance) can also spread into domestic pest insect populations. Scientists at the USDA, Agriculture Research Service, Center for Medical, Agricultural and Veterinary Entomology, Gainesville, Florida, in collaboration with those at Pennsylvania State University have developed a new method for detecting and quantifying inter-species hybridization events. The method involves a novel use of unique SNPs (single-nucleotide polymorphisms) found in the DNA of different species or populations and establishes an efficient protocol to detect and quantify the level of hybridization between genetically distinct wild populations. This hybrid/SNP application has the potential to facilitate risk assessments for spread of invasive species and to direct the development of control strategies for a number native and invasive moth pest species, including those commonly known as "armyworms" that are a problem for many vegetable and turf crops.

Technical Abstract: Invasive insect species can potentially hybridize with closely related native populations to produce new phenotypes with deleterious economic and environmental consequences. Monitoring such events is often problematic because populations that can interbreed are typically sufficiently similar that it is difficult, if not impossible, to distinguish hybrids from parental types by morphology. This study uses the noctuid moth Spodoptera frugiperda (J.E. Smith), or fall armyworm, as a model system to test a new strategy using single-nucleotide polymorphisms (SNPs) to address this issue. The fall armyworm consists of two strains that differ in their host plant preferences. The strains are morphologically indistinguishable and can only be identified by a small number of genetic markers, including the sex-linked Triosephosphate isomerase gene (Tpi). Two SNPs in a Tpi exon were characterized that differed in their strain-specificity but were otherwise similar in structure. Therefore, differences in the frequency of heterozygosity between the two SNPs should reflect differences in the frequency of interstrain hybridizations relative to intrastrain mating. Comparisons of heterozygosity metrics for these loci found that productive mating between strains is 4-5 fold reduced compared to those within strains. In addition, the data indicate that directional interstrain mating biases observed in laboratory studies were probably not a major factor in determining genotype proportions observed in field populations. These findings demonstrate that the differential SNP method can provide a more detailed description of interbreeding between closely related populations in the field, leading to a better assessment of how frequently such events occur and insight into the mating behaviors involved.