Julian Chen

Activation of defense mechanism in wheat by polyphenol oxidase from aphid saliva.

The saliva of two cereal aphids, Sitobion avenae and Schizaphis graminum in third-instar nymphs, was collected after 24 h of feeding by 30 aphids, separately, on artificial diet sachets, and the salivary enzymes were determined. The result showed that polyphenol oxidase (PPO) existed in the saliva of both aphid species, and the enzymatic activities were 6.2 x 10(-3) U/g for S. avenae and 2.37 x 10(-1) U/g for S. graminum, revealing a 38-fold higher activity in the saliva of S. graminum than in the saliva of S. avenae. It was speculated that the higher PPO activity in S. graminum saliva was a contributing factor to the light yellow spot left on the feeding site of the wheat leaf by S. graminum; no such spot was left by S. avenae. After treatment of a wheat seedling with the saliva of S. avenae and S. graminum and PPO at the concentration of aphid saliva, transcript profiling data showed that aphid saliva and PPO significantly induced expression of the genes aos and fps. Because genes aos and fps encode the key enzymes in the defense signal pathways jasmonic acid and terpene signal pathways, respectively, it was deduced that PPO from aphid saliva, as the main elicitor, triggers an appropriate defense response in wheat through jasmonic acid and terpene signal pathways.

Identification and Expression Analysis of Candidate Odorant-Binding Protein and Chemosensory Protein Genes by Antennal Transcriptome of Sitobion avenae

Odorant-binding proteins (OBPs) and chemosensory proteins (CSPs) of aphids are thought to be responsible for the initial molecular interactions during olfaction that mediate detection of chemical signals. Analysis of the diversity of proteins involved comprises critical basic research work that will facilitate the development of sustainable pest control strategies. To help us better understand differences in the olfactory system between winged and wingless grain aphids, we constructed an antennal transcriptome from winged and wingless Sitobion avenae (Fabricius), one of the most serious pests of cereal fields worldwide. Among the 133,331 unigenes in the antennal assembly, 13 OBP and 5 CSP putative transcripts were identified with 6 OBP and 3 CSP sequences representing new S. avenae annotations. We used qPCR to examine the expression profile of these genes sets across S. avenae development and in various tissues. We found 7 SaveOBPs and 1 SaveCSP were specifically or significantly elevated in antennae compared with other tissues, and that some transcripts (SaveOBP8, SaveCSP2 and SaveCSP5) were abundantly expressed in the legs of winged or wingless aphids. The expression levels of the SaveOBPs and SaveCSPs varied depending on the developmental stage. Possible physiological functions of these genes are discussed. Further molecular and functional studies of these olfactory related genes will explore their potential as novel targets for controlling S. avenae.

Genetic Variation Among the Geographic Population of the Grain Aphid, Sitobion avenae (Hemiptera: Aphididae) in China Inferred from Mitochondrial COI Gene Sequence

Abstract In order to characterize the genetic relationship of the geographic populations of Sitobion avenae (Hemiptera: Aphididae) in China, a 588 bp region of the mitochondrial cytochrome oxidase subunit I (mtDNA-COI) gene was sequenced and analyzed among the different geographic populations. 269 individuals were collected from 17 localities in different wheat-growing areas in China that covered most of the range reported for this species. Within the sequence among these geographic populations, 15 polymorphic sites defined 16 distinct haplotypes, ranging in sequence divergence from 0.2% (one nucleotide) to 1.7% (10 nucleotides). Of the 15 variable sites, 12 were transitional substitutions, 2 were transversional substitutions and 1 was transitional and transversional substitution. Phylogenetic analysis showed that all haplotypes were highly interconnected with each other, in absence of phylogeographic structing. Each of 8 haplotypes was found only at one locality, and the other haplotypes were the widespread distributed in the different localities. The higher genetic diversity was found in the northern China populations than that in the southern China populations. The low genetic differentiation (FST=−0.06945-0.69857) and high migration rate (Nm=0.21575-infinite) of Chinese populations suggest that dispersal over long distance is a major factor in the demography of S. avenae.

Wheat (Triticum aestivum L.)-based intercropping systems for biological pest control: a review

Wheat (Triticum aestivum L.) is one of the most cultivated crops in temperate climates. As its pests are mainly controlled with insecticides that are harmful to the environment and human health, alternative practices such as intercropping have been studied for their potential to promote biological control. Based on the published literature, this study aimed to review the effect of wheat-based intercropping systems on insect pests and their natural enemies. Fifty original research papers were obtained from a systematic search of the peer-reviewed literature. Results from a vote-counting analysis indicated that, in the majority of studies, pest abundance was significantly reduced in intercropping systems compared with pure stands. However, the occurrence of their natural enemies as well as predation and parasitism rates were not significantly increased. The country where the studies took place, the type of intercropping and the crop that was studied in the association had significant effects on these results. These findings show that intercropping is a viable practice to reduce insecticide use in wheat production systems. Nevertheless, other practices could be combined with intercropping to favour natural enemies and enhance pest control.

Discovery of English Grain Aphid (Hemiptera: Aphididae) Biotypes in China

ABSTRACT The English grain aphid, Sitobion avenae (F.) (Hemiptera: Aphididae), is an important pest insect of wheat, Triticum aestivum (L.), in China. Grain aphid biotypes are necessary to breed aphid-resistant wheat varieties; however, none have currently been identified. Here, we describe a method to identify grain aphid biotypes and survey the aphid biotype variation in the wheat growth area of China. Clones of S. avenae were collected from 11 locations in China and used to establish culture populations. These populations were then used to assess the resistance of 12 wheat varieties. Based on resistance responses, seven differential hosts were selected to identify the biotype of S. avenue: Amigo, ‘Fengchan No. 3’, Zhong 4 wumang, JP1, L1, 885479-2, and ‘Xiaobaidongmai’. S. avenae was ultimately classified into five biotypes: EGA I, EGA II, EGA III, EGA IV, and EGA V. These methods provide a mechanism to detect the variation and evolution of grain aphids in different wheat-growing locations and also allow for selection of appropriate aphid-resistant germplasm for wheat breeding of commercial wheat cultivars.

Use of slow-release plant infochemicals to control aphids: a first investigation in a Belgian wheat field.

Using infochemicals to develop a push–pull strategy in pest control is a potential way to promote sustainable crop production. Infochemicals from plant essential oils were mixed with paraffin oil for slow release in field experiments on wheat to control the population density of cereal aphids and to enhance their natural enemies. (Z)-3-Hexenol (Z3H) attracted Metopolophum dirhodum and Sitobion avenae, the predominant species on wheat in Belgium, and may be a useful infochemical for aphid control by attracting aphids away from field plots. Release of (E)-β-farnesene (EBF) or a garlic extract (GE) led to a significant decrease in the abundance of wheat aphids. The main natural enemies of cereal aphids found were lacewings (47.8%), hoverflies (39.4%), and ladybirds (12.8%). Ladybird abundance varied little before the end of the wheat-growing season. Our results suggest that these chemicals can form the basis of a “push–pull” strategy for aphid biological control, with GE and EBF acting as a pest- and beneficial-pulling stimulus and Z3H for aphid pulling.

Impact of wheat-mung bean intercropping on English grain aphid (Hemiptera: Aphididae) populations and its natural enemy.

ABSTRACT The effects of intercropping wheat, Triticum aestivum L., with mung bean, Vigna radiate L., on the populations of English grain aphid, Sitobion avenae (F.) (Hemiptera: Aphididae), and its natural enemies were evaluated by field and laboratory experiments. The population densities of aphids and their natural enemies were evaluated in the intercropped field against different row ratio combinations of wheat—mung bean. Results showed that wheat—mung bean intercropping caused a drop in aphid densities, and the ratio 12 wheat:4 mung bean brought about the largest drop (>18%). In addition, the population densities of coccinellids (ladybirds) and parasitoids and the species diversity of all the natural enemies of aphid were higher in the intercropped field than in the field planted only with wheat. However, intercropping did not influence the community indices (evenness and index of dominance concentration) of the natural enemies. Y-tube olfactometer bioassays were carried out in the laboratory to test whether odor blends of host and nonhost plants affect the host selection of S. avenae. Bioassays indicated that both apterous and alate aphids significantly preferred host plant odor over odor blends of host and intercropped species. Hence, the olfactory-based host location of aphids in the field might be affected by intercropping. The intercropping experiment clearly showed that increased crop species diversity suppresses aphid population growth and preserves the population of natural enemies of aphids. Our results also provide support for the “resource concentration hypothesis” and the “enemies hypothesis.”

Evaluation on the resistance to aphids of wheat germplasm resources in China

A collection of more than 200 wheat lines from the main wheat-producing areas of China was evaluated for resistance to wheat aphids, using fuzzy recognition technique in five field experiments over 2 years. The results show that susceptibility to wheat aphids was exhibited in most of the lines tested, and no immune and highly resistant lines to wheat aphids was observed. The average percentage of wheat germplasm lines with resistant, lowly susceptible, moderately susceptible and highly susceptible to aphid were 9.30, 23.15, 42.32, and 25.23%, respectively. 5 moderately resistant wheat germplasm lines to wheat aphids (Lantian18, Lantian20, Lantian22, Lantian00-30 and Shanmai175) were found in Jiangyou experimental station in 2009. More importantly, 2 wheat germplasm lines (Lantian20, Lantian22) with the continuous resistance to wheat aphid in the five experimental stations over 2 years were discovered. Although, resistance of wheat germplasm lines had a close relation to their genetics and inheritance, we also found that the resistance of the same wheat germplasm lines was varied in different experimental stations. It would be helpful to make wheat germplasm selections for breeding programs, especially if they have unique genes that may provide resistance to future biotypes of wheat aphids. A valuable method for evaluating the potential of aphid-resistance for wheat germplasm lines was also confirmed.

Cloning and RNA interference analysis of the salivary protein C002 gene in Schizaphis graminum

Abstract The full-length cDNA of functionally-unknown salivary protein C002 in Schizaphis graminum was cloned using rapid amplification of cDNA ends (RACE) and designated as SgC002 (GenBank accession no. KC977563). It is 767 bp long and encodes a protein of 190 amino acid residues with a predicted mass of 21.5 kDa and a predicted cleavage site of N-terminal signal peptide between the 24th and the 25th residues. SgC002 is specifically expressed in salivary gland with the highest level at the 2nd instar. Introducing SgC002-specific 476-siRNA, but not 546-siRNA to aphids through artificial diet significantly suppressed SgC002 expression. Silencing SgC002 gene led to lethality of the aphid on wheat plants, but not on pure artificial diet. Our study demonstrated that artificial diet-mediated RNAi can be a useful tool for research on the roles of genes in aphid salivary gland, and also provided new insights into the characteristics of C002 in wheat aphids.

Variation in the transmission of barley yellow dwarf virus-PAV by different Sitobion avenae clones in China

Fourteen Sitobion avenae Fabricius (Hemiptera: Aphididae) clonal lines (clones) originating from China were tested for their ability to transmit BYDV-PAV (one isolate from Belgium and another from China) using wheat plants. By sequence analysis, the coat protein gene of BYDV-PAV-BE was distinguishable from BYDV-PAV-CN. All of the clones could transmit BYDV-PAV, and the transmission varied from 24.42% to 66.67% with BYDV-PAV-BE and from 23.55% to 56.18% with BYDV-PAV-CN. These data suggest that S. avenae has no specialty in BYDV-PAV isolate. Significant differences in the transmission frequencies between the clones with BYDV-PAV-BE and BYDV-PAV-CN were observed. The transmission efficiencies of aphid clones from the middle-lower reaches of Yangtze River (AH, HD, HDE, HZ, JZ, JY and SJ) and Yunnan province (YH) were similar. Nevertheless, differences in the virus transmission efficiencies of the clones from northern (ST and STA) and northwestern (QX, SB and XS) regions were assessed. The transmission efficiency of S. avenae from northern and northwestern China, where BYDV impact is more important, was higher than that from the middle-lower reaches of the Yangtze River and Yunnan province. This work emphasizes the importance of considering aphid vector clonal diversity in addition to virus strain variability when assessing BYDV transmission efficiency.