Hessian Fly Research Articles

Multiple quarantine treatment using bale compression and a three-day fumigation to control Hessian fly (Diptera: Cecidomyiidae) in exported hay.

A multiple quarantine treatment was developed to control Hessian fly puparia, Mayetiola destructor (Say), the stage of regulatory concern in exported hay. In a commercial test using 51.589 puparia, no insects survived to the adult stage after exposure to bale compression at 137 kg/cm2 and fumigation with 61 g/28.3 m3 hydrogen phosphide for 3d. The puparia were fumigated in infested wheat seedlings in cloth bags inside compressed timothy bales placed in different locations in three replicate freight containers in a heated building. Fumigant concentrations were 345-522 ppm on day 1; 580-824 ppm on day 2; and 680-861 ppm on day 3. Monitored temperatures were < 20 degrees C in all locations allowing the fumigation temperature to be established at > or = 20 degrees C. Copper detection plate corrosion values were severe inside the freight container doors, and moderate in the middle of bales in all locations, providing visual confirmation of exposure to hydrogen phosphide. Hydrogen phosphide residues in exposed hay bales were found in trace amounts, below the U.S. Environmental Protection Agency tolerance of 0.1 ppm for animal feeds. Timothy hay used in the commercial test is the representative species for all previously exported hay and straw species. The new multiple quarantine treatment is proposed for use with all previously tested bale sizes and wrapper styles for which 3-d fumigation data has been reported, and for bales and wrappers derived from those tested.

Hessian Fly (Mayetiola destructor [Say]) Resistance Identified on Chromosome 1AS in the Spring Wheat (Triticum aestivum L.) Cultivar ‘Louise’

ABSTRACTThe Hessian fly (Mayetiola destructor [Say]) is a major yield‐limiting pest in wheat (Triticum aestivum L.) production systems. Resistant varieties provide the most effective control method. The objectives of this study were to identify the chromosomal location of and molecular markers associated with the Hessian fly resistance from the spring wheat cultivar ‘Louise’. One hundred eighty‐eight F5:6 recombinant inbred lines (RILs) from a Louise (resistant) × ‘Penawawa’ (susceptible) cross were evaluated for resistance to Hessian fly biotype C and a mixed population originating from field collections in the Pacific Northwest (PNW). Eight to 15 plants per RIL were scored for resistance at Purdue University and the University of Idaho. Data were converted to percentages of susceptible plants within each RIL. Louise and Penawawa had averaged susceptibility values of 15 and 100%, respectively. The RIL population ranged from 0 to 100% susceptible. A genetic linkage map consisting of 320 simple sequence repeat and 8530 single nucleotide polymorphism DNA markers was used for quantitative trait locus (QTL) analysis. One QTL, identified as QHf.wak‐1A, was significantly associated with Hessian fly resistance at an average LOD of 26.2 and accounted for 77% of the phenotypic variation. QHf.wak‐1A was localized to a 4.6‐cM region on chromosome 1AS, flanked by markers Xiwb70039 and Xcfd15. Marker, biotype screening, and allelism results indicate that this QTL is different from H9, H11, H5, and H3, but linked to H3 and H5. These data continue to clarify the relationship between Hessian fly genes on chromosome 1AS and would facilitate breeding efforts.

Expression Comparisons of Pathogenesis-Related (PR) Genes in Wheat in Response to Infection/Infestation by Fusarium, Yellow dwarf virus (YDV) Aphid-Transmitted and Hessian Fly

Expression profiles of ten pathogenesis-related (PR) genes during plant defense against Fusarium, Yellow dwarf virus (YDV) aphid-transmitted and Hessian fly (Hf) were compared temporally in both resistant and susceptible genotypes following pathogen infection or insect infestation. Quantitative real-time PCR (qRT-PCR) revealed that PR1, PR2, PR3, PR5, PR6, PR8, PR9, and PR15 appeared to be induced or suppressed independently in response to Fusarium, YDV aphid-transmitted or Hf during the interactions. The PR gene(s) essential to defense against one organism may play little or no role in defense against another pathogen or pest, suggesting the alternative mechanisms may be involved in different interactions of wheat-Fusarium, wheat-YDV aphid-transmitted and wheat-Hf. However, strong up- or down-regulation of PR12 and PR14 encoding low molecular membrane acting protein, defensin and lipid transfer protein (LTP), respectively, had been detected after either pathogen infection or insect infestation, therefore showed broad responses to pathogens and insects. It was postulated that low molecular proteins such as defensins and LTPs might play a role in the early stages of pathogenesis in the signaling process that informs plants about the attack from biotic stresses. In addition, a synergistic action between different PR genes might exist in plants to defense certain pathogens and insects on the basis of comprehensive expression profiling of various pathogenesis-related genes revealed by qRT-PCR in this study.

Seed damage and sources of yield loss by Sitodiplosis mosellana (Diptera: Cecidomyiidae) in resistant wheat varietal blends relative to susceptible wheat cultivars in western Canada

AbstractSpring wheat varieties with the Sm1 gene for resistance to wheat midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae), were compared with susceptible wheat (Triticum Linnaeus; Poaceae) with respect to sources of yield loss and reduction in market value from wheat midge feeding damage. Four resistant varietal blends (90% Sm1 wheat plus 10% susceptible refuge) and four susceptible cultivars were grown in replicated experiments at eight locations in western Canada. Frequencies and 1000-kernel weights of undamaged and midge-damaged seeds were assessed before harvest by dissecting samples of ripe spikes, and after harvest in samples of cleaned grain. Spike data were used to estimate yield losses from reduced weight of damaged seeds and loss of severely damaged seeds (⩽8 mg) at harvest. Among midge-damaged seeds in spikes, few were severely damaged in resistant varietal blends, whereas most were severely damaged in susceptible cultivars. Cleaned, harvested grain of resistant varietal blends and susceptible cultivars had similar frequencies of midge damage and were assessed similar market grades. The primary benefit of midge-resistant wheat was reduced yield loss due to seed damage by wheat midge larvae. Resistant wheat did not protect against loss of market grade, but market value could increase due to larger yields.

Transient Heat Stress Compromises the Resistance of Wheat (Poales: Poaceae) Seedlings to Hessian Fly (Diptera: Cecidomyiidae) Infestation

Heat stress exerts a profound impact on the resistance of plants to parasites. In this research, we investigated the impact of an acute transient heat stress on the resistance of the wheat line 'Molly,' which contains the R gene H13, to an avirulent Hessian fly (Mayetiola destructor (Say)) population. We found that a significant portion of Molly seedlings stressed at 40 degrees C for 6 h during or after the initial Hessian fly larval attack became susceptible to otherwise avirulent insects, whereas unstressed control plants remained 100% resistant. Specifically, 77.8, 73.3, 83.3, and 46.7% of plants heat stressed at 0, 6,12, and 24 h, respectively, after the initial larval attack became susceptible. Biochemical analysis revealed that heat stress caused a transient decrease in 12-oxo-phytodienoic acid, but an increase in salicylic acid accumulation in Molly plants. The change in phytohormones after heat stress and Hessian fly infestation was not observed in 'Newton,' a near-isogenic but Hessian fly susceptible wheat line. Instead, heat stress caused a relatively prolonged reduction in palmitoleic acid. The role of phytohormones in heat-induced loss of wheat resistance was discussed.

Virulence and Biotype Analyses of Hessian Fly (Diptera: Cecidomyiidae) Populations From Texas, Louisiana, and Oklahoma

Hessian fly, Mayetiola destructor (Say, 1817), is a major pest of wheat, and is controlled mainly through deploying fly-resistant wheat cultivars. The challenge for the plant resistance approach is that virulence of Hessian fly populations in the field is dynamic, and wheat cultivars may lose resistance within 6-8 yr. To ensure continuous success of host plant resistance, Hessian fly populations in the field need to be constantly monitored to determine which resistance genes remain effective in different geographic regions. This study investigated five Hessian fly populations collected from Texas, Louisiana, and Oklahoma, where infestation by Hessian fly has been high in recent years. Eight resistance genes, H12, H13, H17, H18, H22, H25, H26, and Hdic, were found to be highly effective against all tested Hessian fly populations in this region, conferring resistance to > or = 80% of plants containing one of these resistance genes. The frequencies ofbiotypes virulent to resistance genes H13 (biotype vH13), H18 (vH18), H21 (vH21), H25 (vH25), H26 (vH26), and Hdic (vHdic) were determined, and were found to vary from population to population, ranging from 0 to 45%. A logistic regression model was established to predict biotype frequencies based on the correlation between the percentages of susceptible plants obtained in a virulence test and the log-odds of virulent biotype frequencies determined by a traditional approach.

Identification and expression profile analysis of putative odorant-binding proteins in Sitodiplosis mosellana (Gehin) (Diptera: Cecidomyiidae)

Odorant binding proteins (OBPs) contribute to the remarkable sensitivity of the insect’s olfactory system and play important roles in the olfactory recognition. The orange blossom midge, Sitodiplosis mosellana is a cereal specialist, and utilizes pheromone and host odorant as a cue for its mating and oviposition. However, OBP genes have not been largely identified in S. mosellana. Based on the sequenced transcriptome database, twenty-six OBP genes were identified in S. mosellana for the first time. Phylogenetic analysis revealed that S. mosellana OBP genes are more closely related to Mayetiola destructor OBP genes than to Aedes aegypti OBP genes. Most OBP genes seemed to be antenna-specific, but differentially expressed in male and female antennae. Three OBP genes (OBP9, OBP19 and OBP23) are leg-specific. And also, most OBP genes have higher expression levels in adults. Only one OBP gene (OBP10) has higher expression levels in larval stages. These findings serve as an important basis for understanding the molecular mechanisms of chemosensory perception.

Sex- and tissue-specific profiles of chemosensory gene expression in a herbivorous gall-inducing fly (Diptera: Cecidomyiidae).

BackgroundThe chemical senses of insects mediate behaviors that are closely linked to survival and reproduction. The order Diptera contains two model organisms, the vinegar fly Drosophila melanogaster and the mosquito Anopheles gambiae, whose chemosensory genes have been extensively studied. Representing a third dipteran lineage with an interesting phylogenetic position, and being ecologically distinct by feeding on plants, the Hessian fly (Mayetiola destructor Say, Diptera: Cecidomyiidae) genome sequence has recently become available. Among plant-feeding insects, the Hessian fly is unusual in ‘reprogramming’ the plant to create a superior food and in being the target of plant resistance genes, a feature shared by plant pathogens. Chemoreception is essential for reproductive success, including detection of sex pheromone and plant-produced chemicals by males and females, respectively.ResultsWe identified genes encoding 122 odorant receptors (OR), 28 gustatory receptors (GR), 39 ionotropic receptors (IR), 32 odorant binding proteins, and 7 sensory neuron membrane proteins in the Hessian fly genome. We then mapped Illumina-sequenced transcriptome reads to the genome to explore gene expression in male and female antennae and terminal abdominal segments. Our results reveal that a large number of chemosensory genes have up-regulated expression in the antennae, and the expression is in many cases sex-specific. Sex-specific expression is particularly evident among the Or genes, consistent with the sex-divergent olfactory-mediated behaviors of the adults. In addition, the large number of Ors in the genome but the reduced set of Grs and divergent Irs suggest that the short-lived adults rely more on long-range olfaction than on short-range gustation. We also report up-regulated expression of some genes from all chemosensory gene families in the terminal segments of the abdomen, which play important roles in reproduction.ConclusionsWe show that a large number of the chemosensory genes in the Hessian fly genome have sex- and tissue-specific expression profiles. Our findings provide the first insights into the molecular basis of chemoreception in plant-feeding flies, representing an important advance toward a more complete understanding of olfaction in Diptera and its links to ecological specialization.

Genetic Diversity and Population Structure of Sitodiplosis mosellana in Northern China

The wheat midge, Sitodiplosis mosellana, is an important pest in Northern China. We tested the hypothesis that the population structure of this species arises during a range expansion over the past 30 years. This study used microsatellite and mitochondrial loci to conduct population genetic analysis of S. mosellana across its distribution range in China. We found strong genetic structure among the 16 studied populations, including two genetically distinct groups (the eastern and western groups), broadly consistent with the geography and habitat fragmentation. These results underline the importance of natural barriers in impeding dispersal and gene flow of S. mosellana populations. Low to moderate genetic diversity among the populations and moderate genetic differentiation (F ST = 0.117) between the two groups were also found. The populations in the western group had lower genetic diversity, higher genetic differentiation and lower gene flow (F ST = 0.116, Nm = 1.89) than those in the eastern group (F ST = 0.049, Nm = 4.91). Genetic distance between populations was positively and significantly correlated with geographic distance (r = 0.56, P<0.001). The population history of this species provided no evidence for population expansion or bottlenecks in any of these populations. Our data suggest that the distribution of genetic diversity, genetic differentiation and population structure of S. mosellana have resulted from a historical event, reflecting its adaptation to diverse habitats and forming two different gene pools. These results may be the outcome of a combination of restricted gene flow due to geographical and environmental factors, population history, random processes of genetic drift and individual dispersal patterns. Given the current risk status of this species in China, this study can offer useful information for forecasting outbreaks and designing effective pest management programs.

The adult head morphology of the hessian flyMayetiola destructor(diptera, cecidomyiidae)

Cover illustration. Mayetiola destructor is a major pest of wheat in Europe, North Africa and North America. In this issue of the Journal of Morphology, Schneeberg et al. (pp. 1299-1311) investigate the adult head structures of the cecidomyiid fly and compared their findings with evolutionarily less successful families within Bibionomorpha. The cover image shows a histological cross section of the head of Mayetiola destructor (Diptera, Cecidomyiidae).

The adult head morphology of the hessian flyMayetiola destructor(diptera, cecidomyiidae)

The adult head of the Hessian fly Mayetiola destructor was examined and described in detail. Morphological features are evaluated with respect to phylogenetic implications and possible effects of miniaturisation. Preserved groundplan features of Diptera are the orthognathous orientation of the head, the vestiture of small microtrichia (possible autapomorphy), filiform antennae inserted frontally between the compound eyes, the presence of a clypeolabral muscle (possible autapomorphy), the presence of labellae (autapomorphy), and the presence of only one premental retractor. Potential synapomorphies of the groups assigned to Bibionomorpha are the origin of M. tentorioscapalis medialis on the frons and the loss of M. craniolacinialis. Further apomorphies of Cecidomyiidae identified in Mayetiola are the unusually massive anterior tentorial arm, the absence of the labro-epipharyngeal food channel, the absence of the lacinia, and the presence of antennal sensilla connected by a seta, a feature not known from any other group of Diptera. The very large size of the compound eyes (in relation to the entire head surface) and the complete loss of ocelli are possible effects of miniaturization. The large size of the brain (in relation to the cephalic lumen), the unusual shape of the optic lobes, and the absence of the frontal ganglion as a separate structure are probably also linked with size reduction.

Genome-wide association mapping for five major pest resistances in wheat

Insect pests cause substantial damage to wheat production in many wheat-producing areas of the world. Amongst these, Hessian fly (HF), Russian wheat aphid (RWA), Sunn pest (SP), wheat stem saw fly (WSSF) and cereal leaf beetle (CLB) are the most damaging in the areas where they occur. Historically, the use of resistance genes in wheat has been the most effective, environmentally friendly, and cost-efficient approach to controlling pest infestations. In this study, we carried out a genome-wide association study with 2518 Diversity Arrays Technology markers which were polymorphic on 134 wheat genotypes with varying degrees of resistance to the five most destructive pests (HF, RWA, SP, WSSF and CLB) of wheat, using mixed linear model (MLM) analysis with population structure as a covariate. We identified 26 loci across the wheat genome linked to genes conferring resistance to these pests, of which 20 are potentially novel quantitative trait loci with significance values which ranged between 5 × 10−3 and 10−11. We used an in silico approach to identify probable candidate genes at some of the genomic regions and found that their functions varied from defense response with transferase activity to several genes of unknown function. Identification of potentially new loci associated with resistances to pests would contribute to more rapid marker-aided incorporation of new and diverse genes to develop new varieties with improved resistance against these pests.

A genome-wide analysis of transcripts in a 2BS.2RL wheat-rye translocation during Hessian fly infestation

The Hessian fly [Mayetiola destructor (Say)] biotype L is the most damaging pest to wheat (Triticum aestivum L.). The long arm of rye chromosome 2 (2RL) has been transferred to common wheat, in the form of 2BS.2RL wheat-rye translocations. 2RL carries gene(s) for resistance to Hessian fly (biotype L), representing a promising target for engineered resistance. The objective of this study was to examine changes in gene expression in near-isogenic lines (NILs) differing by the presence (resistant NIL) or absence (susceptible NIL) of 2RL under Hessian fly infestation. Gene expression was detected using an Affymetrix 3′ IVT wheat genome array. Separate comparisons of data sets generated from the array were performed to identify transcripts involved in the defense pathways. Diverse resistant NIL-specific transcripts including ethylene-responsive factor-like transcription factors and zinc-finger proteins were discovered. Evidence of the enrichment of gene ontologies associated with hydrolase was found in resistant NIL during Hessian fly infestation. The gene information identified in this study would be an important resource in growing our understanding of the resistance mechanisms and for cloning candidate genes.

Mobilization of lipids and fortification of cell wall and cuticle are important in host defense against Hessian fly.

BackgroundWheat – Hessian fly interaction follows a typical gene-for-gene model. Hessian fly larvae die in wheat plants carrying an effective resistance gene, or thrive in susceptible plants that carry no effective resistance gene.ResultsGene sets affected by Hessian fly attack in resistant plants were found to be very different from those in susceptible plants. Differential expression of gene sets was associated with differential accumulation of intermediates in defense pathways. Our results indicated that resources were rapidly mobilized in resistant plants for defense, including extensive membrane remodeling and release of lipids, sugar catabolism, and amino acid transport and degradation. These resources were likely rapidly converted into defense molecules such as oxylipins; toxic proteins including cysteine proteases, inhibitors of digestive enzymes, and lectins; phenolics; and cell wall components. However, toxicity alone does not cause immediate lethality to Hessian fly larvae. Toxic defenses might slow down Hessian fly development and therefore give plants more time for other types of defense to become effective.ConclusionOur gene expression and metabolic profiling results suggested that remodeling and fortification of cell wall and cuticle by increased deposition of phenolics and enhanced cross-linking were likely to be crucial for insect mortality by depriving Hessian fly larvae of nutrients from host cells. The identification of a large number of genes that were differentially expressed at different time points during compatible and incompatible interactions also provided a foundation for further research on the molecular pathways that lead to wheat resistance and susceptibility to Hessian fly infestation.

Wheat Mds-1 encodes a heat-shock protein and governs susceptibility towards the Hessian fly gall midge

Gall midges induce formation of host nutritive cells and alter plant metabolism to utilize host resources. Here we show that the gene Mayetiola destructor susceptibility-1 on wheat chromosome 3AS encodes a small heat-shock protein and is a major susceptibility gene for infestation of wheat by the gall midge M. destructor, commonly known as the Hessian fly. Transcription of Mayetiola destructor susceptibility-1 and its homoeologs increases upon insect infestation. Ectopic expression of Mayetiola destructor susceptibility-1 or induction by heat shock suppresses resistance of wheat mediated by the resistance gene H13 to Hessian fly. Silencing of Mayetiola destructor susceptibility-1 by RNA interference confers immunity to all Hessian fly biotypes on normally susceptible wheat genotypes. Mayetiola destructor susceptibility-1-silenced plants also show reduced lesion formation due to infection by the powdery mildew fungus Blumeria graminis f. sp. tritici. Modification of susceptibility genes may provide broad and durable sources of resistance to Hessian fly, B. graminis f. sp. tritici, and other pests.

Genetic association of OPRgenes with resistance to Hessian fly in hexaploid wheat

BackgroundHessian fly (Mayetiola destructor) is one of the most destructive pests of wheat. The genes encoding 12-oxo-phytodienoic acid reductase (OPR) and lipoxygenase (LOX) play critical roles in insect resistance pathways in higher plants, but little is known about genes controlling resistance to Hessian fly in wheat.ResultsIn this study, 154 F6:8 recombinant inbred lines (RILs) generated from a cross between two cultivars, ‘Jagger’ and ‘2174’ of hexaploid wheat (2n = 6 × =42; AABBDD), were used to map genes associated with resistance to Hessian fly. Two QTLs were identified. The first one was a major QTL on chromosome 1A (QHf.osu-1A), which explained 70% of the total phenotypic variation. The resistant allele at this locus in cultivar 2174 could be orthologous to one or more of the previously mapped resistance genes (H9, H10, H11, H16, and H17) in tetraploid wheat. The second QTL was a minor QTL on chromosome 2A (QHf.osu-2A), which accounted for 18% of the total phenotypic variation. The resistant allele at this locus in 2174 is collinear to an Yr17-containing-fragment translocated from chromosome 2N of Triticum ventricosum (2n = 4 × =28; DDNN) in Jagger. Genetic mapping results showed that two OPR genes, TaOPR1-A and TaOPR2-A, were tightly associated with QHf.osu-1A and QHf.osu-2A, respectively. Another OPR gene and three LOX genes were mapped but not associated with Hessian fly resistance in the segregating population.ConclusionsThis study has located two major QTLs/genes in bread wheat that can be directly used in wheat breeding programs and has also provided insights for the genetic association and disassociation of Hessian fly resistance with OPR and LOX genes in wheat.

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.

Serine and cysteine protease-like genes in the genome of a gall midge and their interactions with host plant genotypes

Proteases play important roles in a wide range of physiological processes in organisms. For plant-feeding insects, digestive proteases are targets for engineering protease inhibitors for pest control. In this study, we identified 105 putative serine- and cysteine-protease genes from the genome of the gall midge Mayetiola destructor (commonly known as Hessian fly), a destructive pest of wheat. Among the genes, 31 encode putative trypsins, 18 encode putative chymotrypsins, seven encode putative cysteine proteases, and the remaining may encode either other proteases or protease homologues. Developmental stage- and tissue-specific expression profiles of the genes encoding putative trypsins, chymotrypsins, and cysteine proteases were determined by quantitative reverse-transcription PCR. Comparative analyses of stage- and tissue-specific expression patterns suggested that several genes are likely to encode digestive proteases in the M. destructor larval gut, including genes encoding putative trypsins MDP3, MDP5, MDP9, MDP24, MDP48, MDP51, MDP57, MDP61, MDP71, and MDP90; genes encoding putative chymotrypsins MDP1, MDP7, MDP8, MDP18, MDP19, and MDP20; and genes encoding putative cysteine proteases MDP95 and MDP104. The expression of some protease genes was affected by plant genotypes. Genes encoding trypsins MDP3, MDP9, and MPD23, chymotrypsins MDP20 and MDP21, and cysteine proteases MDP99 and MDP104 were upregulated in M. destructor larvae feeding in resistant plants, whereas genes encoding trypsins MDP12, MDP24, and MDP33, and chymotrypsins mdp8, mdp15, and mdp16 were downregulated in M. destructor larvae feeding in resistant plants. This study provides a foundation for further comparative studies on proteases in different insects, and further characterization of M. destructor digestive proteases and their interactions with host plants, as well as potential targets for transgenic wheat plants.

Identification of a novel gene, H34, in wheat using recombinant inbred lines and single nucleotide polymorphism markers

Hessian fly (HF), Mayetiola destructor, is an important pest of wheat (Triticum aestivum L.) worldwide. Because it has multiple biotypes that are virulent to different wheat HF resistance genes, pyramiding multiple resistance genes in a cultivar can improve resistance durability, and finding DNA markers tightly linked to these genes is essential to this process. This study identified quantitative trait loci (QTLs) for Hessian fly resistance (HFR) in the wheat cultivar 'Clark' and tightly linked DNA markers for the QTLs. A linkage map was constructed with single nucleotide polymorphism and simple sequence repeat markers using a population of recombinant inbred lines (RILs) derived from the cross 'Ning7840'×'Clark' by single-seed descent. Two QTLs associated with resistance to fly biotype GP were identified on chromosomes 6B and 1A, with the resistance alleles contributed from 'Clark'. The QTL on 6B flanked by loci Xsnp921 and Xsnp2745 explained about 37.2% of the phenotypic variation, and the QTL on 1A was flanked by Xgwm33 and Xsnp5150 and accounted for 13.3% of phenotypic variation for HFR. The QTL on 6B has not been reported before and represents a novel wheat gene with resistance to HF, thus, it is designated H34. A significant positive epistasis was detected between the two QTLs that accounted for about 9.5% of the mean phenotypic variation and increased HFR by 0.16. Our results indicated that different QTLs may contribute different degrees of resistance in a cultivar and that epistasis may play an important role in HFR.

Palaeolimnological impacts of early prehistoric farming at Lough Dargan, County Sligo, Ireland

This study provides a unique method of inquiry for archaeological investigation with an aim to assess the intensity and effects of Neolithic and Bronze Age farming practices at Lough Dargan, northwest Ireland, through a multi-proxy analysis of a lake sediment core. Chironomid (non-biting midge fly) subfossils and lake sediment geochemistry (δ13C, δ15N and C:N ratios) were used to assess changes in limnological conditions through time. The limnological data were compared with macroscopic charcoal concentration and pollen data to examine the potential influence that early farmers had on a freshwater lake system within a prehistorically active catchment. Results from the chironomid analysis show that the first substantial period of agricultural activity in the early Neolithic (c. 3730–3190 BC) resulted in a temporary shift to more eutrophic lake conditions. There is evidence of animal husbandry with substantial levels of animal waste reaching the lake, leaving an imprint in the geochemical record of increased δ15N values and decreased δ13C values and C:N ratios during this time. The chironomid community reverted back to its pre-impacted state c. 3190 BC in response to a period of reduced farming (c. 3390–3000 BC) which eventually led to a distinct lull in activity, with possible cessation of farming from 3000 to 2700 BC. A return to eutrophic conditions coincided with the gradual return of agriculture, with more permanently altered lake conditions dominating from 2400 BC, even during a 250-year period of reduced human activity commencing at c. 1440 BC. Increased sedimentation rate, along with increases in δ13C, δ15N and C:N, the presence of chironomid taxa indicative of erosion, more eutrophic lake conditions and high concentrations of macroscopic charcoal all point to more intensive land use practices during the Bronze Age. Palaeolimnological data exhibited an immediate response to intensified farming during this time, and were especially responsive to pastoral farming due either to scale of activity or proximity to the lakeside. The success of this study demonstrates the effectiveness of palaeolimnological analysis in the investigation of prehistoric farming. This approach will help inform Neolithic and Bronze Age land-use practice and human–environment relations in the region, and highlights the potential for chironomid-based archaeological research.