Localization and characterization of 170 BAC-derived clones and mapping of 94 microsatellites in the Hessian fly

Molecular characterization of eliminated chromosomes in Hessian fly (Mayetiola destructor (Say))

Like other cecidomyiid Diptera, Hessian fly has stable S chromosomes and dispensable E chromosomes that are retained only in the germ line. Amplified fragment length polymorphisms (AFLP), suppressive subtractive hybridization (SSH), fluorescent in-situ hybridization (FISH), and sequencing were used to investigate similarities and differences between S and E chromosomes. More than 99.9% of AFLP bands were identical between separated ovary and somatic tissue, but one band was unique to ovary and resembled Worf, a non-LTR retrotransposon. Arrayed clones, derived by SSH of somatic from ovarian DNA, showed no clones that were unique to ovary. FISH with BAC clones revealed a diagnostic banding pattern of BAC positions on both autosomes and both sex chromosomes, and each E chromosome shared a pattern with one of the S chromosomes. Sequencing analysis showed that E chromosomes are nearly identical to S chromosomes, since no sequence could be confirmed to belong only to E chromosomes. There were a few questionably E-specific sequences that are candidates for further investigation. Thus, the E chromosomes appear to be derived from S chromosomes by the acquisition or conversion of sequences that produce the negatively heteropycnotic region around the centromere.

The evolution of Hessian fly from the Old World to the New World: Evidence from molecular markers

Eighteen polymorphic microsatellite loci and 11 single-nucleotide polymorphisms were genotyped in 1,095 individual Hessian fly specimens representing 23 populations from North America, southern Europe, and southwest Asia. The genotypes were used to assess genetic diversity and interrelationship of Hessian fly populations. While phylogenetic analysis indicates that the American populations most similar to Eurasian populations come from the east coast of the United States, genetic distance is least between (Alabama and California) and (Kazakhstan and Spain). Allelic diversity and frequency vary across North America, but they are not correlated with distance from the historically documented point of introduction in New York City or with temperature or precipitation. Instead, the greatest allelic diversity mostly occurs in areas with Mediterranean climates. The microsatellite data indicate a general deficiency for heterozygotes in Hessian fly. The North American population structure is consistent with multiple introductions, isolation by distance, and human-abetted dispersal by bulk transport of puparia in infested straw or on harvesting equipment.

Use of microsatellite and SNP markers for biotype characterization in Hessian fly

Exploration of the biotype structure of Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae), would improve our knowledge regarding variation in virulence phenotypes and difference in genetic background. Microsatellites (simple sequence repeats) and single-nucleotide polymorphisms (SNPs) are highly variable genetic markers that are widely used in population genetic studies. This study developed and tested a panel of 18 microsatellite and 22 SNP markers to investigate the genetic structure of nine Hessian fly biotypes: B, C, D, E, GP, L, O, vH9, and vH13. The simple sequence repeats were more polymorphic than the SNP markers, and their neighbor-joining trees differed in consequence. Microsatellites suggested a simple geographic association of related biotypes that did not progressively gain virulence with increasing genetic distance from a founder type. Use of the k-means clustering algorithm in the STRUCTURE program shows that the nine biotypes comprise six to eight populations that are related to geography or history within laboratory cultures.

Population structure and the colonization route of one of the oldest North American invasive insects: stories from the worn road of the Hessian fly, Mayetiola destructor (Say)

An integral part to understanding the biology of an invasive species is determining its origin, particularly in pest species. As one of the oldest known invasive species, the goals of this study were to evaluate the evidence of a westward expansion of Hessian fly into North America, from a potential singular introduction event, and the population genetic structure of current populations. Levels of genetic diversity and population structure in the Hessian fly were compared across North America, Europe, North Africa, Western Asia, and New Zealand. Furthermore, Old World populations were evaluated as possible sources of introduction. We tested diversity and population structure by examining 18 microsatellite loci with coverage across all four Hessian fly chromosomes. Neither genetic diversity nor population genetic structure provided evidence of a westward movement from a single introduction in North America. Introduced populations in North America did not show identity or assignment to any Old World population, likely indicating a multiple introduction scenario with subsequent gene flow between populations. Diversity and selection were assessed on a chromosomal level, with no differences in diversity or selection between chromosomes or between native and introduced populations.

Biological and molecular characterization of Hessian fly (Diptera: Cecidomyiidae) from Israel

Samples of a dipteran pest of wheat were tested to confirm identity, describe local populations and suggest the use of deploying resistance (R) genes in wheat cultivars for control of Mayetiola destructor, Hessian fly (HF). Morphological evaluation of adults and a free-choice oviposition preference test documenting that females overwhelmingly preferred to oviposit on wheat instead of barley supported they were HF. Using the cytochrome c oxidase subunit I (coxI), the Barcoding Region, nine haplotypes were revealed. Two were found only in the Israeli collections and averaged 3% sequence divergence compared to the other seven haplotypes found in the United States, Israel and Syria. In evaluations of virulence, the Israeli HF in culture was virulent to 11 of the 19 (R) genes tested, and complementation analysis documented that, for four of the R genes tested, the Israeli HF shared loci for virulence with HF from the United States. Levels of HF infestation at seven Israeli fields were at least at the 5-8% level, which historically has indicated a significant yield loss. Microsatellite genotyping of the five HF collections from Israel revealed mixed populations in Israel that are distinctly separate from the single population in Syria.

A neo-sex chromosome that drives postzygotic sex determination in the hessian fly (Mayetiola destructor)

Two nonoverlapping autosomal inversions defined unusual neo-sex chromosomes in the Hessian fly (Mayetiola destructor). Like other neo-sex chromosomes, these were normally heterozygous, present only in one sex, and suppressed recombination around a sex-determining master switch. Their unusual properties originated from the anomalous Hessian fly sex determination system in which postzygotic chromosome elimination is used to establish the sex-determining karyotypes. This system permitted the evolution of a master switch (Chromosome maintenance, Cm) that acts maternally. All of the offspring of females that carry Cm-associated neo-sex chromosomes attain a female-determining somatic karyotype and develop as females. Thus, the chromosomes act as maternal effect neo-W's, or W-prime (W') chromosomes, where ZW' females mate with ZZ males to engender female-producing (ZW') and male-producing (ZZ) females in equal numbers. Genetic mapping and physical mapping identified the inversions. Their distribution was determined in nine populations. Experimental matings established the association of the inversions with Cm and measured their recombination suppression. The inversions are the functional equivalent of the sciarid X-prime chromosomes. We speculate that W' chromosomes exist in a variety of species that produce unisexual broods.