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

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 (> 8%). 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".

Discovery of English grain aphid (Hemiptera: Aphididae) biotypes in China.

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. avenae: 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.

Coordinative mediation of the response to alarm pheromones by three odorant binding proteins in the green peach aphid Myzus persicae.

Odorant binding proteins (OBPs) play an essential role for insect chemosensation in insect peripheral nervous systems of antennae. Each antennal sensilla contains more than one OBP at high concentrations but the interactions and cooperation between co-localized OBPs are rarely reported. In present study, we cloned, expressed and purified eight OBPs of the green peach aphid Myzus persicae. The effects of knocking down the expression of these OBP genes by RNAi on the electrophysiological and behavioural responses of M. persicae to the aphid alarm pheromone, (E)-ß-farnesene (EßF) were investigated. The results showed that the aphids could still be repelled by EßF when the expression of each of three OBP genes was individually knocked down. However, the simultaneous knockdown of MperOBP3/7/9 expression significantly reduced the electrophysiological response and the repellent behaviours of M. persicae to EßF than the single OBP gene knockdown (P < 0.05). Rather than a normal saturation binding curve of individual OBP, the binding curve of MperOBP3/7/9 is bell-shaped with a higher affinity for the fluorescent probe N-phenyl-1-naphthylamine (1-NPN). The competitive binding assays confirmed that MperOBP3, MperOBP7, MperOBP9 and MperOBP3/7/9 mixture exhibited a stronger binding affinity for EßF, than for sex pheromones and plant volatiles with a dissociation constant of 2.5 µM, 1.1 µM, 3.9 µM and 1.0 µM, respectively. The competitive binding curve of MperOBP3/7/9 mixture to EßF is shallow without bottom plateau, suggesting a conformational change and a rapid dissociation after the displacement of all 1-NPN (in vivo after the saturation binding of all OBPs by EßF). The interaction between OBPs and formation of a heterogeneous unit may facilitate the delivery EßF to the OR at electrophysiological and behavioural levels during insect odorant signal transduction thus mediate M. persicae response to the alarm pheromone EßF.

Impact of aphid alarm pheromone release on virus transmission efficiency: When pest control strategy could induce higher virus dispersion.

Aphids cause serious damages to crops not only by tacking sap but also by transmitting numerous viruses. To develop biological control, the aphid alarm pheromone, namely E-ß-farnesene (EßF), has been demonstrated to be efficient to repel aphids and as attract beneficials, making it a potential tool to control aphid pests. Considering aphids also as virus vectors, changes of their behavior could also interfere with the virus acquisition and transmission process. Here, a combination of two aphid species and two potato virus models were selected to test the influence of EßF release on aphid and virus dispersion under laboratory conditions. EßF release was found to significantly decrease the population of Myzus persicae and Macrosiphum euphorbiae around the infochemical releaser but simultaneously also increasing the dispersal of Potato Virus Y (PVY). At the opposite, no significant difference for Potato Leaf Roll Virus (PLRV) transmission efficiency was observed with similar aphid alarm pheromone releases for none of the aphid species. These results provide some support to carefully consider infochemical releasers not only for push-pull strategy and pest control but also to include viral disease in a the plant protection to aphids as they are also efficient virus vectors. Impact of aphid kinds and transmission mechanisms will be discussed according to the large variation found between persistent and non persistent potato viruses and interactions with aphids and related infochemicals.

[Ecological effects of wheat-oilseed rape intercropping combined with methyl salicylate release on Sitobion avenae and its main natural enemies].

In order to explore the effects of wheat-oilseed rape intercropping in combining with methyl salicylate (MeSA) release on Sitobion avenae and its main natural enemies, a field experiment was conducted at the Tai'an Experimental Station of Shandong Agricultural University in East China from October 2008 to June 2010 to study the temporal dynamics of S. avenae and its main natural enemies as well as the ecological control effect on the aphid. In the plots of intercropping combined with MeSA release, the S. avenae apterae population reached a peak about 12 d in advance of the control, but the peak value was significantly lower than that of the control. The average annual number of S. avenae apterae per 100 wheat tillers decreased in the order of wheat monoculture > wheat-oilseed rape intercropping > MeSA release > wheat-oilseed rape intercropping combined with MeSA release. Moreover, the total number of ladybeetles was the highest in the plots of intercropping combined with MeSA release. The population densities of aphid parasitoids reached a peak about 10 d in advance of the control, which could play a significant role in controlling S. avenae at the filling stage of wheat. Taking the biological control index (BCI) as a quantitative indicator, and with the ladybeetles and parasitoids as the dominant control factors in fields, it was observed that wheat-oilseed rape intercropping combined with MeSA release could suppress the population increase of S. avenae apterae effectively from the heading to filling stages of wheat.

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.

[Effects of wheat leaf surface waxes on the feeding of two wheat aphid species].

By using GC-MS and bioassay techniques, this paper studied the effects of different wheat varieties (cultivars) leaf surface waxes on the feeding of wheat aphids Sitobion avenae and Rhopalosiphum padi. The results showed that the leaf surface waxes of wheat varieties (cultivars) SN80, SN18 and Zimail2 could stimulate the feeding of test aphids, while SN87 could not. GC-MS analysis showed that the chemical composition of leaf surface waxes differed with wheat varieties (cultivars). The main components were long chain alkanes, and others were 7-tetradecene, 8-pentadecanone, ethyl citrate, tetradecanoic acid ethyl ester, and hexadecanoic acid ethyl ester. The bioassay found that alkanes (> C17), 7-tetradecene and 8-pentadecanone could act as strong stimulants to the feeding of the aphids, while ethyl citrate, tetradecanoic acid ethyl ester and hexadecanoic acid ethyl ester didn't have stimulation to S. avenae, neither tetradecanoic acid ethyl ester and hexadecanoic acid ethyl ester to R. padi.