Yun Duan

Sub‐lethal effects of four neonicotinoid seed treatments on the demography and feeding behaviour of the wheat aphid Sitobion avenae

BACKGROUND Neonicotinoids are widely used as seed treatments in wheat fields against the grain aphid (Sitobion avenae F.) in China. Due to the degradation of neonicotinoids in wheat plants, wheat aphids are more likely to be exposed to low concentrations of neonicotinoids over long periods. It is therefore expected that neonicotinoids, aside from acute (lethal) effects, may also cause a range of sub-lethal effects on this pest. RESULTS The growth and fertility of S. avenae feeding on wheat plants treated with a sub-lethal concentration (LC10 ) of imidacloprid, dinotefuran, thiacloprid and thiamethoxam were not greatly affected. However, the population growth parameters of S. avenae were significantly reduced at median lethal concentration (LC50 ). Electronic penetration graph recordings showed a higher percentage of no probing phase and shorter phloem sap ingestion phase on the wheat plants treated with LC10 and LC50 concentrations. CONCLUSION The results indicate that even low concentrations of neonicotinoid treatments on wheat seeds have long-term, adverse effects on wheat aphid. As such, neonicotinoid seed treatments have far greater effects on wheat aphids than estimated by acute toxicity tests. These results benefit our understanding on the subtle effects of the four tested neonicotinoids when applied as seed treatments.

Global Transcriptome Analysis of Orange Wheat Blossom Midge, Sitodiplosis mosellana (Gehin) (Diptera: Cecidomyiidae) to Identify Candidate Transcripts Regulating Diapause

Background Many insects enter a developmental arrest (diapause) that allows them to survive harsh seasonal conditions. Despite the well-established ecological significance of diapause, the molecular basis of this crucial adaptation remains largely unresolved. Sitodiplosis mosellana (Gehin), the orange wheat blossom midge (OWBM), causes serious damage to wheat throughout the northern hemisphere, and sporadic outbreaks occur in the world. Traits related to diapause appear to be important factors contributing to their rapid spread and outbreak. To better understand the diapause mechanisms of OWBM, we sequenced the transcriptome and determined the gene expression profile of this species. Methodology/Principal Findings In this study, we performed de novo transcriptome analysis using short-read sequencing technology (Illumina) and gene expression analysis with a tag-based digital gene expression (DGE) system. The sequencing results generated 89,117 contigs, and 45,713 unigenes. These unigenes were annotated by Blastx alignment against the NCBI non-redundant (nr), Clusters of orthologous groups (COG), gene orthology (GO), and the Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. 20,802 unigenes (45.5% of the total) matched with protein in the NCBI nr database. Two digital gene expression (DGE) libraries were constructed to determine differences in gene expression profiles during diapause and non-diapause developmental stages. Genes related to diapause were analyzed in detail and in addition, nine diapause-related genes were analyzed by real time PCR. Conclusions/Significance The OWBM transcriptome greatly improves our genetic understanding and provides a platform for functional genomics research of this species. The DGE profiling data provides comprehensive information at the transcriptional level that facilitates our understanding of the molecular mechanisms of various physiological aspects including development and diapause stages in OWBM. From this study it is evident that various genes coding metabolic enzymes are crucial for diapause and metamorphosis.

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.

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 insects 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.

Flight Performance of the Orange Wheat Blossom Midge (Diptera: Cecidomyiidae)

ABSTRACT The orange wheat blossom midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae), is a chronic wheat pest worldwide. Adult S. mosellana engage in short-distance flight, but also exploit weather patterns for long-distance dispersal. However, little is known about the flight performance of S. mosellana, and the effects of the biotic and abiotic factors that influence its flight activity. In this study, we explored the active flight potential of S. mosellana under various environmental factors using a 26-channel computer-monitored flight mill system. The most suitable temperature for flight and flight distance was 16-24°C; flight duration peaked at 16°C while speed peaked at 28°C. Flight performance gradually declined between 10 and 400 lux light intensity. More than 50% individuals of 1-d-old females flew >500 m, while only 24% of males flew >500 m. One-day-old S. mosellana had stronger flight ability than that of 2-d-old individuals. This research showed that S. mosellana possessed strong enough flight ability that they can fly to a high altitude and then disperse via moving air currents. These results can aid in forecasting S. mosellana outbreak.

Transcriptome analysis of molecular mechanisms responsible for light-stress response in Mythimna separata (Walker)

Light is an important environmental signal for most insects. The Oriental Armyworm, Mythimna separata, is a serious pest of cereal crops worldwide, and is highly sensitive to light signals during its developmental and reproductive stages. However, molecular biological studies of its response to light stress are scarce, and related genomic information is not available. In this study, we sequenced and de novo assembled the transcriptomes of M. separata exposed to four different light conditions: dark, white light (WL), UV light (UVL) and yellow light (YL). A total of 46,327 unigenes with an average size of 571 base pairs (bp) were obtained, among which 24,344 (52.55%) matched to public databases. The numbers of genes differentially expressed between dark vs WL, dark vs UVL, dark vs YL, and UVL vs YL were 12,012, 12,950, 14,855, and 13,504, respectively. These results suggest that light exposure altered gene expression patterns in M. separata. Putative genes involved in phototransduction-fly, phototransduction, circadian rhythm-fly, olfactory transduction, and taste transduction were identified. This study thus identified a series of candidate genes and pathways potentially related to light stress in M. separata.

The genetic diversity of SMLS (Sitobion miscanthi L type symbiont) and its effect on the fitness, mitochondrial DNA diversity and Buchnera aphidicola dynamic of wheat aphid, Sitobion miscanthi (Hemiptera: Aphididae)

SMLS (Sitobion miscanthi L type symbiont) is a recently discovered aphid secondary symbiont. Using evidence extracted from 16S rRNA sequences, previous studies indicate that SMLS is the most widely distributed and most recently transferred secondary symbiont in Chinese Sitobion miscanthi populations. Here, we further investigated genetic diversity among SMLS geographic strains with multiloci data. Furthermore, the influence of SMLS on S. miscanthi was uncovered with ecological and evolutionary evidence. The results indicated that there was limited influence of infection with SMLS on variation and evolutionary patterns of S. miscanthi mitochondrial DNA. By hemolymph injection, the SMLS‐infected and SMLS‐uninfected S. miscanthi clones with the identical genetic background were built in this study. Although similar Buchnera aphidicola dynamics were observed between SMLS‐infected and SMLS‐uninfected S. miscanthi population, B. aphidicola density of SMLS‐infected S. miscanthi population was always significantly higher than SMLS‐uninfected ones. The results of fitness measurements indicated that under laboratory rearing conditions, transfection of SMLS could confer modest advantages to some fitness components of S. miscanthi, that is, total number of offspring, longevity, age of first reproduction and weight of adult. However, as SMLS is not strictly associated with S. miscanthi, further investigations are needed to uncover the mechanisms responsible for this inconceivable association.

Spectral sensitivity of the compound eyes of Anomala corpulenta motschulsky (Coleoptera: Scarabaeoidea)

Abstract The scarab beetle, Anomala corpulenta Motschulsky (Coleoptera: Scarabaeoidea), is a widespread and destructive pest in China. Vision is one of the most important means of acquiring information about the external environment. In order to contribute to the understanding of the perception of visual stimuli in this species, the light sensitivity and spectral responses of the scarab beetle, A. corpulenta, were measured by using an electroretinogram (ERG) technique. In total, 14 monochromatic light intensities, between 340 and 605 nm, were applied to the compound eyes of A. corpulenta under varying levels of adaptation to dark and light conditions. The results showed that all light stimuli induced an ERG response, with varied amplitudes. The spectral sensitivity curve of dark-adapted eyes showed one major peak (~400 nm; near-ultraviolet), a secondary peak (from 498 to 562 nm; yellow-green) and the third peakat 460 nm. By contrast, in light-adapted eyes, only a near-UV peak was observed. From these results, we conclude that the compound eye of A. corpulenta is likely to have at least three spectral types of photoreceptor. Significance of differences were also recorded in the responses of male and female compound eyes, as well as diurnally and nocturnally. The amplitude of ERG in response to white-light stimuli varied with the light intensity: The stronger the luminance, the higher the ERG value. This suggests that the compound eye of A. corpulenta adapts quickly to changing light conditions, enabling A. corpulenta to maintain nocturnal activities.

Resistance Grading Method and Evaluation in Wheat Varieties to Orange Wheat Blossom Midge,Sitodiplosis mosellana(Diptera:Cecidomyidae) in China

To simplify the method of identifying resistance in winter wheat varieties to orange wheat blossom midge, Sitodiplosis mosellana(Diptera: Cecidomyidae), we compared the traditional method for resistance assessment and a resistance grading method based on percentage of infested spike(ISP) in field experiments carried out in Luoyang, Henan Province, China from2008 to 2012, using 236–417 wheat varieties each year. The correlation analysis showed that yield loss was highly associated with ISP. Under high density of insect population, the ISP grading method was more effective in identifying the resistance to the insect than the traditional method, and the resistance to S. mosellana was divided into five levels, namely immune(ISP = 0), highly resistant(0 ISP 20), moderately resistant(20 ≤ ISP 40), Medium(40 ≤ ISP 60), susceptible(60 ≤ ISP 80), and highly susceptible(ISP ≥ 80). Using ISP grading method, resistance to S. mosellana was evaluated in 25 commercial wheat varieties with growing area larger than 2×105hectares. All varieties were susceptible or highly susceptible to S. mosellana, but Jingmai 66 was highly resistant. This result indicates not only the possibility of replacement of the traditional resistance evaluation method by the new simple and high-efficient grading method, but also the risk of S. mosellana burst due to extreme shortage of resistant resource in Chinese wheat varieties.