Screening and Evaluation of Different Wheat Cultivars for Resistance to Sitobion avenae at Seedling and Adult-plant Stages

In order to clarify the relationships between seedling and adult-plant resis- tance to English grain aphid Sitobion avenae （Fabricius）, 94 wheat cultivars were screened and evaluated based on aphid number ratio through artificial inoculation in greenhouse and natural infection in field from 2010 to 2012. The results indicated that 43 wheat cultivars were resistant to aphid at different levels, of which two dis- played high resistance, eight moderate resistance and 33 low resistance at adult- plant stage. Meanwhile, 45 wheat cultivars exhibited aphid resistance at seedling stage, including 5 highly-resistant cultivars, 16 moderately-resistant cultivars and 24 low-resistant cultivars. Thirty wheat cultivars showed resistance to aphids to different degrees at both seedling and adult-plant stages, accounting for 31.91% of all tested wheat cultivars, especially that C273 and Lanmai （Shaanxi Zhashui） showed high aphid resistance. Aphid number ratio of wheat cultivars at seedling stage had an extremely significant positive correlation with that at adult-plant stage. Additionally, 66 wheat cultivars exhibited the same resistance to aphids at both seedling and adult-plant stages, accounting for 70.21% of all cultivars. The study demonstrated that inoculation test at seedling stage in greenhouse is a reliable method for identi- fying wheat resistance to S. avenae.

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

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.

EPG Comparison of Sitobion avenae (Fab.) Feeding Behavior on Three Wheat Varieties

This article was to study the potential resistance mechanism of three different wheat varieties （Ww2730, Xiaoyan 22 and Batis） in the seedling stage to Sitobion avenae. The aphid feeding behavior was ascertained by stylet penetration activities monitoring using the electrical penetration graph （EPG） technique. When the aphids feed on Ww2730 seedlings, the time for the 1st duration probing was later than that on Xiaoyan 22 and Batis significantly, and the number of interrupted probing before the 1st duration probing was more than that on Xiaoyan 22 and Batis significantly, and the 1st duration probing was shorter than that on Xiaoyan 22 and Batis significantly. The durations of the stylet pierce from the extra- to the intra-cellular （pd Ⅱ-1） on Ww2730 and Xiaoyan 22 were longer than those on Batis significantly. The duration of the potential drop （pd） in C wave on Ww2730 was longer than that on Xiaoyan 22 and Batis significantly. The times and duration of the G wave （ingestion in xylem） on Ww2730 were more and longer than those on Xiaoyan 22 and Batis significantly. The times of spot G wave on Batis was more than that on Ww2730 significantly, but the duration of spot G was shorter than that on Xiaoyan 22 and Ww2730 significantly. The total time of E1 wave, the longest duration of E1 fractions, and the mean duration time of E1 fractions that followed E2 wave on Xiaoyan 22 and Batis were all significantly longer than those on Ww2730. There was no difference of the mean duration of the 1st E1 wave on the 3 varieties, but the mean durations of other E1 wave on Ww2730 and Xiaoyan 22 were shorter than those on Batis significantly. The other wave parameters, including times and durations of F and E2 were all not different on the 3 wheat varieties. It is suggested that the resistance mechanism of wheat variety Ww2730 to S. avenae is a restriction factor of feeding in epidermis, the thicker cell wall in mesophyll, and secondary metabolites or nutrition unbalance in phloem in the seedling phase. The resistance mechanism of Xiaoyan 22 is thicker cell wall and more cell layer in mesophyll in the seedling phase. The feeding strategy of S. avenae against the resistance of Ww2730 was to shorten the second duration of secrete watery salivation to xylem than the first.

Comparison of the potential rate of population increase of brown and green color morphs of Sitobion avenae （Homoptera： Aphididae） on barley infected and uninfected with Barley yellow dwarf virus

Life tables of brown and green color morphs of the English grain aphid, Sitobion avenae （Fabricius） reared on barley under laboratory conditions at 20 ＋ 1℃,65% ± 5% relative humidity and a photoperiod of 16 ： 8 h （L ： D） were compared. The plants were either： （i） infected with the Barley yellow dwarf virus （BYDV）; （ii） not infectedwith virus but previously infested with aphids; or （iii） healthy barley plants, which were not previously infested with aphids. Generally, both color morphs of S. avenae performedsignificantly better when fed on BYDV-infected plants than on plants that were virus free but had either not been or had been previously infested with aphids. Furthermore,when fed on BYDV-infected plants, green S. avenae developed significantly faster and had a significantly shorter reproductive period than the brown color morph. There wereno significant differences in this respect between the two color morphs ofS. avenae when they were reared on virus-free plants that either had been or not been previously infestedwith aphids. These results indicate that barley infected with BYDV is a more favorable host plant than uninfected barley for both the color morphs ofS. avenae tested, particularly the green color morph.

燕麦红叶病介体蚜虫获毒前后差异表达基因分析

燕麦(Avena sativa L.)红叶病是由蚜蚧体传播的大麦黄短病毒(Barley yellow dwarf virus,BYDV)引起的病毒病,已成为燕麦生产上的常发病害。为探讨BYDV与蚜虫互作机制,以麦长管蚜(Sitobion avenae)为研究对象,通过高通量转录组(RNA-Seq)测序和分析技术对其获毒前后的转录组进行了测定和分析。结果表明,在获毒前后转录组中共获得622个差异表达基因,获毒蚜虫中有406个上调基因,216个下调基因。共有53个基因比对上NCBI蛋白数据库并获得功能注释;其中36个被聚类到GO的三大功能中;32个被注释到KEGG的77个代谢通路中。根据差异表达基因的GO和KEGG分析,麦长管蚜代谢过程和催化活性的相关基因明显上调。筛选出与细胞免疫和免疫信号路径相关的基因8个,其中75%的基因表达上调。BYDV和介体昆虫麦长管蚜存在互作关系,病毒入侵后可能通过代谢活动相关基因的上调和免疫相关基因的差异表达而影响麦长管蚜的代谢活动和免疫反应过程。

Influence of Garlic Intercropping or Active Emitted Volatiles in Releasers on Aphid and Related Beneficial in Wheat Fields in China

In order to develop biological control of aphids by a ＂push-pull＂ approach, intercropping using repellent emitting plants was developed in different crop and associated plant models. Garlic is one of the potential plant that could be inserted in crops to decrease the pest occurrence in neighboring crop plots. In this study, field works were conducted in wheat fields in Langfang Experimental Station, Hebei Province in China from October 2009 to July 2010 during wheat developmental season. The effect of wheat intercropping with garlic but also the volatiles emission on the incidence of the English grain aphid, Sitobion avenae Fabricius （Homoptera： Aphididae） was assessed. Natural beneficial occurrence and global yields in two winter wheat varieties that were susceptible or resistant to cereal aphid were also determined comparing to control plots without the use of garlic plant intercrop nor semiochemical releaser in the fields. S. avenae was found to be lower in garlic oil blend treatment （GOB）, diallyl disulfide treatment （DD） and wheat-garlic intercropping treatment （WGI） when compared to the control plots for both two varieties （P〈0.01）. Both intercropping and application of volatile chemicals emitted by garlic could improve the population densities of natural enemies of cereal aphid, including ladybeetles and mummified aphids. Ladybeetle population density in WGI, GOB and mummified aphids densities in WGI, DD were significantly higher than those in control fields for both two varieties （P〈0.05）. There were significant interactions between cultivars and treatments to the population densities of S. avenae. The 1 000-grain weight and yield of wheat were also increased compared to the control. Due to their potential alternatives as a biological control agent against cereal aphid, garlic intercropping and related emitted volatiles are expected to contribute to the further improvement of integrated pest management systems and to potentially reduce the amount of traditional synthetic pesticides applied in wheat fields.

Aphidophagous guilds on nettle （Urtica dioica） strips close to fields of green pea, rape and wheat

The common nettle （Urtica dioica L.） is a perennial and cosmopolitan plant species and is known to be the source of food for a great diversity of insects. To understand the importance of the nettle in agro-ecosystems, a field experiment was carried out in an experimental farm at Gembloux （Belgium） to study the effect of nettle margin strips on aphid and aphidophagous populations in close field crops, namely wheat （Triticum aestivum L.）, green pea （Pisum sativum L.） and rape （Brassicae napus L.）. The aphids and related beneficial populations were weekly assessed, from March to August 2005, by visual observations in two plots per field crop. A higher abundance of aphidophagous beneficials was collected in nettle strips when compared to the field crops. Particularly, the presence of predatory anthocorids, mirids and green lacewings was observed on nettle only. Nevertheless, the most abundant aphid predatory family, the Coccinellidae, was distributed in both environments, in nettle strips and in crop fields. The field margin supported a significantly higher density ofHarmonia axyridis than the field crops. In contrast, the field crops, green pea particularly, supported a higher density of Coccinella septempunctata. The distribution of the aphidophagous species, mainly the ladybirds, was discussed in relation to the host plant and related aphid species and their potential effect on integrated pest management.

Increased nitrogen fertilization inhibits the biocontrol activity promoted by the intercropping partner plant

The examination of the compatibility between agricultural practices and biocontrol activities is crucial for establishing an efficient,eco-friendly,and sustainable pest management program.In this study,we examined the population dynamics of two specialist aphids,the English grain aphid(Sitobion avenae)on potted wheat and the pea aphid(Acyrthosiphon pisum)on potted alfalfa,as well as the biocontrol activity of a generalist predator,the harlequin ladybird beetle(Harmonia axyridis).We investigated their responses to the presence of the intercropping partner plant species(alfalfa and wheat,respectively)through plant volatiles or visual cues at three nitrogen fertilizer levels in a greenhouse.In the absence of the predator,the English grain aphid population growth rate increased significantly with increasing nitrogen levels,whereas the pea aphid population increased significantly more slowly in response to high nitrogen levels.The English grain aphid and pea aphid population dynamics were unaffected by the presence of the intercropping partner.However,the presence of the intercropping partner enhanced the control of both aphid populations by the harlequin ladybird beetle.Increasing nitrogen fertilizer levels decreased the predation rates,which were otherwise increased by the intercropping partner.The beneficial effects of the intercropping partner were eventually non-existent at the highest nitrogen level tested.These results imply that the interaction between the presence of intercropping partner and the nitrogen fertilizer application affects the biocontrol activity of the natural enemies of insect pests.Thus,the compatibility between agricultural intensification and biocontrol strategies in integrated pest management programs need to be investigated.