Hessian fly (Diptera: Cecidomyiidae) virulence in Louisiana: assessment of field populations from 2023 to efficacy of 27 Hessian fly resistance genes in wheat.

The Hessian fly, Mayetiola destructor (Say), is one of the most important insect pest plaguing wheat (Triticum aestivum, L) producers across the United States and around the world. Genetic resistance is the stalwart for control of Hessian fly. However, new genotypes (biotypes) arise in deployment of wheat containing resistance genes, so field populations must be evaluated periodically to provide information on the efficacy of those deployed genes. Louisiana (LA), with its diverse agricultural landscape, is not exempt from the challenges posed by this destructive pest. We previously documented the resistance response of wheat lines harboring Hessian fly resistance (H) genes against field populations collected in 2008 from across the southeastern United States, including Iberville Parish, LA. In the spring of 2023, we reevaluated the resistance response of 27 H genes from the field populations collected from Iberville Parish, LA, and compared the results with those observed in 2008. Sixteen H genes showed comparable resistance to the field populations from both years. While 3 of the H genes, H11, H23, and H24, showed a significant decrease in resistance, 2 genes, H16 and H31, had marked increase in resistance. Furthermore, 6 additional H genes were evaluated in 2023, with 4 showing >70% resistance. Our results clearly identify a total of 20 H genes that are moderate to highly effective against the 2023 Hessian fly population from Iberville Parish, LA. The resistance response documented in this study offers valuable information to wheat breeders in the region for effective management of this insect pest.

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.

Effectiveness of Genes for Hessian Fly (Diptera: Cecidomyiidae) Resistance in the Southeastern United States.

The Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae), is the most important insect pest of wheat (Triticum aestivum L. subsp. aestivum) in the southeastern United States, and the deployment of genetically resistant wheat is the most effective control. However, the use of resistant wheat results in the selection of pest genotypes that can overcome formerly resistant wheat. We have evaluated the effectiveness of 16 resistance genes for protection of wheat from Hessian fly infestation in the southeastern United States. Results documented that while 10 of the genes evaluated could provide protection of wheat, the most highly effective genes were H12, H18, H24, H25, H26, and H33. However, H12 and H18 have been reported to be only partially effective in field evaluations, and H24, H25, and H26 may be associated with undesirable effects on agronomic traits when introgressed into elite wheat lines. Thus, the most promising new gene for Hessian fly resistance appears to be H33. These results indicate that identified highly effective resistance in wheat to the Hessian fly is a limited resource and emphasize the need to identify novel sources of resistance. Also, we recommend that the deployment of resistance in gene pyramids and the development of novel strategies for engineered resistance be considered.

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.

Hessian Fly (Diptera: Cecidomyiidae) Mortality in Export Bale Compressors and Response to a Hydrogen Phosphide and Carbon Dioxide Gas Mixture.

Hessian fly, Mayetiola destructor (Say), puparial mortality was evaluated in three modern hay compressors that produce compressed standard and large-size bales for export to Asia-Pacific countries. Pressure on bales ranged from 93.4 to 139.4 kg/cm2, causing 90.0-99.9% mortality of 10,891-23,164 puparia. Puparial response to a cylinderized hydrogen phosphide (1.8-2%) and carbon dioxide (97.8-98%) gas mixture was evaluated as a potential quarantine treatment using 2-4 d-exposures to low, medium, and high doses of 0.73-0.86, 1.05-1.26, and 1.39-1.56 mg/liter, and temperatures of 5.87±1.14, 9.84±0.05, 16.14±0.14, and 20.35±0.11°C. Accumulative concentration multiplied by time products (mg h/liter) at all fumigation temperatures for low, medium, and high fumigant doses were 34.9-37.7, 52.2-54.3, and 67.9-73.1 for 2 d; 52.7-60.6, 77.9-89.2, and 102.1-110.7 for 3 d; and 69.9-82.0, 99.4-118.2, and 132.3-146.8 for 4 d, respectively. An increase in mortality was significantly related to an increase in fumigation duration at 5, 10, and 15°C, and an increase in fumigant dose at 10 and 15°C. Puparial mortality ranged from 97.2 to 100% at all doses and durations at 20°C with no survivors at the highest dose for 3 d and the mid- and highest dose for 4 d. Bale compression is currently used in the first phase of a multiple quarantine treatment to control potential Hessian fly contaminants in exported hay. The novel fumigant may have application as a single quarantine treatment for noncompressed, standard exported bales.

Survival of Hessian fly (Diptera: Cecidomyiidae) puparia exposed to simulated hay harvest conditions, location and windrow drying in Washington and California.

Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae) puparia are of regulatory concern in exported hay, and drying after harvest was evaluated as a cultural control technique for bales shipped from the western states. In total 16,836; 31,122; and 48,051 puparia were tested under drying conditions in environmental chambers, open air on location, and hay windrows, respectively. Regression lines for percentage of total adults emerging from puparia exposed to simulated drying conditions for 1-7 d in environmental chambers was significant for 1 September, Kittitas Valley, WA; 3 June, East Columbia Basin, WA; 15 May and 15 July, San Joaquin Valley, CA; and 15 May, 20 July, and 15 September, Imperial Valley, CA. In open air drying on location for 1-7 d, total percentage of puparia surviving to adults for all exposure days was 0.4% for 18 June, Kittitas Valley; 1.2% for 15 May, San Joaquin Valley; and 0% for 16 July, Imperial Valley; and significantly different between controls and exposure durations. In hay windrow drying for 1-6 d, total percentage of puparia surviving to adults for all exposure days was 5.4% on 28 June and 24.2% on 7 September in timothy, Phleum pretense, in the Kittitas Valley; 3.8% on 28 June in timothy in the East Columbia Basin; 2.2% on 20 July in alfalfa, Medicago sativa, in the San Joaquin Valley; and 6.3% on 21 July in Sudan grass, Sorghum bicolor sudanensis, in the Imperial Valley. The number of puparia surviving to adults in open air drying and in windrows was significantly different between controls and exposure durations for all test dates and locations. Puparial survival in field tests was related to mild temperatures and high humidities. Hay drying with subsequent field baling, storage, and export bale compression is discussed in relation to a systems approach for quarantine control of Hessian fly in exported hay.

Characterization of new loci for Hessian fly resistance in common wheat.

The discovery of several new loci for resistance to Hessian fly was reported here. QHf.uga-6AL, the late HR61 was recognized from wheat cultivar 26R61 on the distal end of 6AL with resistance to both biotypes E and vH13. It is the first gene or QTL found on this particular chromosome. QHf.uga-3DL and QHf.uga-1AL, physically assigned to the deletion bins 3DL2-0.27-0.81 and 1AL1-0.17-0.61, respectively, were detected for resistance to biotype vH13. Both QTL should represent new loci for Hessian fly resistance and the latter was detectable only in the late seedling stage when tolerance was evident. In addition, QHf.uga-6DS-C and QHf.uga-1AS had minor effect and were identified from the susceptible parent AGS 2000 for resistance to biotype E and vH13, respectively. QHf.uga-6DS-C is different from the known gene H13 on 6DS and QHf.uga-1AS is different from H9 gene cluster on 1AS. These loci also might be new components of Hessian fly resistance, although their LOD values were not highly significant. The QTL detections were all conducted on a RIL mapping population of 26R61/AGS 2000 with good genome coverage of molecular markers. The strategy used in the current study will serve as a good starting point for the discovery and mapping of resistance genes including tolerance to the pest and the closely linked markers will certainly be useful in selecting or pyramiding of these loci in breeding programs.

Virulence in Hessian fly (Diptera: Cecidomyiidae) field collections from the southeastern United States to 21 resistance genes in wheat.

Genetic resistance in wheat, Triticum aestivum L., is the most efficacious method for control of Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae). However, because of the appearance of new genotypes (biotypes) in response to deployment of resistance, field collections of Hessian fly need to be evaluated on a regular basis to provide breeders and producers information on the efficacy of resistance (R) genes with respect to the genotype composition of Hessian fly in regional areas. We report here on the efficacy of 21 R genes in wheat to field collections of Hessian fly from the southeastern United States. Results documented that of the 21 R genes evaluated only five would provide effective protection of wheat from Hessian fly in the southeastern United States. These genes were H12, H18, H24, H25, and H26. Although not all of the 33 identified R genes were evaluated in the current study, these results indicate that identified genetic resistance to protect wheat from Hessian attack in the southeastern United States is a limited resource. Historically, R genes for Hessian fly resistance in wheat have been deployed as single gene releases. Although this strategy has been successful in the past, we recommend that in the future deployment of combinations of highly effective previously undeployed genes, such as H24 and H26, be considered. Our study also highlights the need to identify new and effective sources of resistance in wheat to Hessian fly if genetic resistance is to continue as a viable option for protection of wheat in the southeastern United States.

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.

Identification of sex pheromone components of the hessian fly, Mayetiola destructor.

Coupled gas chromatographic (GC)-electroantennographic detection (EAD) analyses of ovipositor extract of calling Hessian fly, Mayetiola destructor, females revealed that seven compounds elicited responses from male antennae. Four of the compounds-(2S)-tridec-2-yl acetate, (2S,10Z)-10-tridecen-2-yl acetate, (2S,10E)-10-tridecen-2-yl acetate, and (2S,10E)-10-tridecen-2-ol-were identified previously in female extracts. Two new EAD-active compounds, (2S,8Z,10E)-8,10-tridecadien-2-yl acetate and (2S,8E,10E)-8,10-tridecadien-2-yl acetate, were identified by GC-mass spectroscopy (MS) and the use of synthetic reference samples. In a Y-tube bioassay, a five-component blend (1 ng (2S)-tridec-2-yl acetate, 10 ng (2S,10E)-10-tridecen-2-yl acetate, 1 ng (2S,10E)-10-tridecen-2-ol, 1 ng (2S,8Z,10E)-8,10-tridecadien-2-yl acetate, and 1 ng (2S,8E,10E)-8,10-tridecadien-2-yl acetate) was as attractive to male Hessian flies as a similar amount of female extract (with respect to the main compound, (2S,10E)-10-tridecen-2-yl acetate). The five-component blend was more attractive to male flies than a three-component blend lacking the two dienes. Furthermore, the five-component blend was more attractive than a blend with the same compounds but that contained one tenth the concentration of (2S,8E,10E)-8,10-tridecadien-2-yl acetate (more accurately mimicking the ratios found in female extract). This suggests that the ratios emitted by females might deviate from those in gland extracts. In a field-trapping experiment, the five-component blend applied to polyethylene cap dispensers in a 100:10 microg ratio between the main component and each of the other blend components attracted a significant number of male Hessian flies. Also, a small-plot field test demonstrated the attractiveness of the five-component blend to male Hessian flies and suggests that this pheromone blend may be useful for monitoring and predicting Hessian fly outbreaks in agricultural systems.

A lectin-like wheat gene responds systemically to attempted feeding by avirulent first-instar Hessian fly larvae.

Through gene-for-gene interactions, wheat plants respond to specific biotypes of Hessian fly upon the initiation of first-instar larval feeding. Leaves of plants containing the H9 resistance gene responded to avirulent biotype L. larvae with rapid changes in the levels of several mRNA transcripts and initiation of an incompatible interaction. A low-copy gene, Hfr-1 (Hessian fly-response gene 1), responded with increased mRNA levels for two days before returning to preinfestation levels by day five. Hfr-1 mRNA was constitutively expressed in uninfested control plants as well as in plants infested with virulent larvae. The cDNA sequence was similar to a maize gene encoding a beta-glucosidase aggregating factor (BGAF), to jacalin-like mannose-binding lectins, and to several plant genes that respond to microbial infections. The potential roles of Hfr-1 in defending wheat against Hessian fly damage are discussed.