Seasonal occurrence of Aphis glycines and physiological responses of soybean plants to its feeding

The soybean aphid Aphis glycines Matsumura （Hemiptera： Aphididae） is an important pest of soybean in China. To monitor and manage this pest effectively it is neces-sary to understand its population dynamics and demographics, as well as the physiological responses of soybean plants to its feeding. In this study, using field surveying and suction-trap monitoring, we investigated the population dynamics of the soybean aphid in Xiuyan County, Liaoning Province in northeastern China during 2009-2012. The results indicatedthat the population dynamics of the soybean aphid followed a unimodal curve distribution, with the insect generally colonizing soybean fields from the middle of June to early Julyand the population reaching a peak between early July and early August. On the whole, soybean aphids occurred in suction-traps at least 2 weeks earlier than they were foundin field surveys. A total of 72 alates were collected by suction-trapping over the 4 years, with the earliest alate captures occurring on 28 May in 2009, 2011, 2012 and 4 June in 2010. The life table parameters clearly showed that this aphid had a short doubling time （4.73 ± 0.21 days）, and 7.36± 0.98 nymphs were produced by a soybean aphid adult during its lifetime （13.57 ± 0.30 days）. Finally, biochemical assays indicated that the amount of malondialdehyde and the activities of four defense-related enzymes in soybean leavessignificantly changed between 0 day and 7 days of aphid infestation. Polyphenol oxidase （PPO） and catalase （CAT） activities increased more dramatically after 1 day of aphid feed-ing. In addition, significantly higher levels of superoxide dismutase and CAT were found after aphid feeding for 7 days, whereas there was no significant change in the activitiesof peroxidase and PPO. Consequently, this study will be beneficial in determining the seasonal occurrence of the soybean aphid and selecting insect-resistant soybean varieties,and thus in developing a theoretical framework for appropriate management strategies.     

High nymphal host density and mortality negatively impact parasitoid complex during an insect herbivore outbreak

Insect herbivore outbreaks frequently occur and this may be due to factors that restrict top-down control by parasitoids, for example, host-parasitoid asynchrony, hyperparasitization, resource limitation and climate. Few studies have examined hostparasitoid density relationships during an in sect herbivore outbreak in a n atural ecosystem with diverse parasitoids. We studied parasitization patterns of Cardiaspina psyllids during an outbreak in a Eucalyptus woodland. First, we established the trophic roles of the parasitoids through a species-specific multiplex PCR approach on mummies from which parasitoids emerged. Then, we assessed host-parasitoid density relationships across three spatial scales (leaf, tree and site) over one yeas We detected four endoparasitoid species of the family Encyrtidae (Hymenoptera);two primary parasitoid and one heteronomous hyperparasitoid Psyllaephagus species (the latter with female development as a primary parasitoid and male development as a hyperparasitoid), and the hyperparasitoid Coccidoctonuspsyllae. Parasitoid development was host-synchronized, although synchrony between sites appeared constrained during winter (due to temperature differences). Parasitization was predominantly driven by one primary parasitoid species and was mostly inversely host-density dependent across the spatial scales. Hyperparasitization by C. psyllae was psyllid-density dependent at the site scale, however, this only impacted the rarer primary parasitoid. High larval parasitoid mortality due to density-dependent nymphal psyllid mortality (a consequence of resource limitation) compounded by a summer heat wave was incorporated in the assessment and resulted in density independence of host-parasitoid relationships. As such, high larval parasitoid mortality during insect herbivore outbreaks may contribute to the absence of host density-dependent parasitization during outbreak events.     

Expressing an (E)-β-farnesene synthase in the chloroplast of tobacco affects the preference of green peach aphid and its parasitoid

(E)-β-Famesene(EβF) synthase catalyses the production of EβF,which for many aphids is the main or only component of the alarm pheromone causing the repellence of aphids and also functions as a kairomone for aphids' natural enemies.Many plants possess EβF synthase genes and can release EβF to repel aphids.In order to effectively recruit the plant-derived EβF synthase genes for aphid control,by using chloroplast transit peptide(CTP) of the small subunit of Rubisco(rbcS) from wheat(Triticum aestivum L.),we targeted AαβFS1,an EβF synthase gene from sweet wormwood(Artemisia annua L),to the chloroplast of tobacco to generate CTP + AαβFS1 transgenic lines.The CTP +AαβFS1 transgenic tobacco plants could emit EβF at a level up to 19.25 ng/day per g fresh tissues,4-12 fold higher than the AαβFS1 transgenic lines without chloroplast targeting.Furthermore,aphid/parasitoid behavioral bioassays demonstrated that the CTP + AαβFS1 transgenic tobacco showed enhanced repellence to green peach aphid(Myzus persicae) and attracted response of its parasitoid Diaeretiella rapae,thus affecting aphid infestation at two trophic levels.These data suggest that the chloroplast is an ideal subcellular compartment for metabolic engineering of plant-derived EβF synthase genes to generate a novel type of transgenic plant emitting an alarm pheromone for aphid control.     

Influence of cornicle droplet secretions of the cabbage aphid,Brevicoryne brassicae,on parasitism behavior of na＇fve and experienced Diaeretiella rapae

Insects have evolved amazing methods of defense to ward off enemies. Many aphids release cornicle secretions when attacked by predators and parasitoids. These se cretions contain an alarm pheromone that alerts other colony members of danger, thereby providing indirect fitness benefits to the releaser. In addition, contact with cornicle se cretions could also threaten an attacker and could provide direct fitness to the releaser. However, cornicle secretions may also be recruited as a kairomonal cue by aphid natural enemies. In this study, we investigated the effect of the cornicle droplet volatiles of the cabbage aphid, Brevicoryne brassicae （L.）, on the hostsearching behavior of naive and experienced female Diaeretiella rapae （M＇Intosh） parasitoids in olfactometer studies. In addition, we evaluated the role ofB. brassicae cornicle droplets on the oviposition prefer ence of the parasitoid in a twochoice bioassay. Naive females did not exhibit any preference between volatiles from aphids secreting cornicle droplets over nonsecreting aphids, while experienced parasitoids exploited the secretions in their host location. Experienced females were also able to choose volatiles from both secreting and nonsecreting aphids over clean air, while this ability was not observed in naive females. Although secretion of cornicle droplets did not influence the percentage of first attack in either naive or experienced females, the success of attack （i.e. resulting in a larva） was significantly different between secreting and nonsecreting aphids in the case of experienced parasitoids.     

Genetic Diversity of Soybean and the Establishment of a Core Collection Focused on Resistance to Soybean Cyst Nematode

Soybean cyst nematode （SCN; Heterodera glycines） Is one of the most Important pests affecting soybean production. The best method of control of SCN is through the development of resistant cultlvars. However, limited progress has been made in soybean breeding In China because most modern cultlvars have no resistance to SCN. The distribution and phenotype of 432 immune or highly resistant Chinese accessions were surveyed and a primary core collection was selected as a representative sample for further analyses. Using evenly distributed simple sequence repeat markers, five selection methods were applied to the primary core collection and the optimal method was chosen to establish a core collection, which consisted of 28 accessions. These encompassed 70.8% of the ailelic variation present in the overall resistant collection. The 28 accessions differed from the reference resistant accessions at the genomlc level, Indicating that Chinese resistant accessions are distinct from known resistant accessions. This applied core collection provides a rational framework for undertaking diversity surveys, using genetic variation for the investigation of complex traits and for the discovery of novel traits.     

The evolutionary ecology of symbiont-conferred resistance to parasitoids in aphids

Abstract Aphids may harbor a wide variety of facultative bacterial endosymbionts. These symbionts are transmitted maternally with high fidelity and they show horizontal trans-mission as well, albeit at rates too low to enable infectious spread. Such symbionts need to provide a net fitness benefit to their hosts to persist and spread. Several symbionts haveachieved this by evolving the ability to protect their hosts against parasitoids. Reviewing empirical work and some models, I explore the evolutionary ecology of symbiont-conferredresistance to parasitoids in order to understand how defensive symbiont frequencies are maintained at the intermediate levels observed in aphid populations. I further show thatdefensive symbionts alter the reciprocal selection between aphids and parasitoids by augmenting the heritable variation for resistance, by increasing the genetic specificity of thehost-parasitoid interaction, and by inducing environment-dependent trade-offs. These effects are conducive to very dynamic, symbiont-mediated coevolution that is driven by frequency-dependent selection. Finally I argue that defensive symbionts represent a problem for biological control of pest aphids, and I propose to mitigate this problem byexploiting the parasitoids＇ demonstrated ability to rapidly evolve counteradaptations to symbiont-conferred resistance.     

The price of protection:a defensive endosymbiont impairs nymph growth in the bird cherry-oat aphid,Rhopalosiphum padi

Bacterial endosymbionts have enabled aphids to adapt to a range of stressors,but their effects in many aphid species remain to be established.The bird cherry-oat aphid,Rhopalosiphum padi(Linnaeus),is an important pest of cereals worldwide and has been reported to form symbiotic associations with Serratia symbiotica and Sitobion miscanthi L-type symbiont endobacteria,although the resulting aphid phenotype has not been described.This study presents the first report of R.padi infection with the facultative bacterial endosymbiont Hamiltonella defensa.Individuals of R.padi were sampled from populations in Eastern Scotland,UK,and shown to represent seven R.padi genotypes based on the size of polymorphic microsatellite markers;two of these genotypes harbored H.defensa.In parasitism assays,survival of H.defensa-infected nymphs following attack by the parasitoid wasp Aphidius colemani(Viereck)was 5 fold higher than for uninfected nymphs.Aphid genotype was a major determinant of aphid performance on two Hordeum species,a modern cultivar of barley H.vulgare and a wild relative H.spontaneum,although aphids infected with H.defensa showed 16%lower nymph mass gain on the partially resistant wild relative compared with uninfected individuals.These findings suggest that deploying resistance traits in barley will favor the fittest R.padi genotypes,but symbiontinfected individuals will be favored when parasitoids are abundant,although these aphids will not achieve optimal performance on a poor quality host plant.     

When parasitoids deal with the spatial distribution of their hosts: consequences for both partners

Insect parasitoids developing inside hosts face a true challenge: hosts are scattered in the field and their localization and selection require the use of complex and sometime confusing information. It was assumed for a long time that small-brained organisms like parasitoids have evolved simple and efficient behavioral mechanisms, leading them to be adapted to a given ecological situation, for example, the spatial distribution o f hosts in the habitat. However, hosts are not static and their distribution may also vary through generations and within the life of parasitoid individuals. We investigated if and how parasitoids deal with such a spatial com plexity in a m esocosm experiment. We used the Aphidius rhopalosiphi/Sitobion avenae parasitoid/host system to investigate if parasitoid females experiencing different host aggregation levels exhibit different foraging behaviors independently of the number of hosts in the environment. We showed that A. rhopalosiphi females exploited hosts more intensively both within and among patches at higher host aggregation levels. We discussed the adaptiveness of such behaviors in the light of evolution and biological control.     

An assessment of interspecific competition between two introduced parasitoids of Diaphorina citri (Hemiptera: Liviidae) on caged citrus plants

Two parasitoids attacking nymphs of Asian citrus psyllid,Diaphorina citri Kuwayama (Hemiptera:Liviidae),Tamarixia radiata (Waterston)(Hymenoptera:Eulophi- dae)and Diaphoreneyrtus aligarhensis (Shafee,Alam &Agarwal)(Hymenoptera:Encyrtidae)are being released in California,USA in a classical biological control program. To evaluate the effect of multiple parasitoid species on D.citri mortality,we conducted mesocosm experiments under controlled conditions using a complete block design with 6 treatments (D.cirri nymphs exposed to:no parasitoids;D.aligarhensis or T.radiata alone;D.aligarhensis or T.radiata released first (by 48 h);and both species released simultaneously).Parasitism of D.citri nymphs by T.radiata exceeded 60%and was unchanged when D.aligarhensis were present.Parasitism by D.aligarhensis was greatest when T. radiata was absent (-28%)and was reduced in all treatments with T.radiata present (<3%).D.cirri mortality and parasitoid-related mortality olD.citri was consistent across parasitoid treatments.Laboratory results suggest that competition between D.aligarhensis and T.radiata is asymmetric and favors T.radiata.It may be difficult for D.aligarhensis to contribute significantly to D.cirri biological control where T.radiata is present.However, results reported here suggest that competition between T.radiata and D.aligarhensis is not likely to reduce parasitism by T.radiata or reduce parasitoid-induced mortality of D.citri.     

From laboratory to the field: consistent effects of experience on host location by the fruit fly parasitoid Diachasmimorpha kraussii (Hymenoptera: Braconidae)

Associative learning is well documented in Hymenopteran parasitoids, where it is thought to be an adaptive mechanism for increasing successful host location in complex environments. Based on this learning capacity, it has been suggested that providing prerelease training to parasitoids reared for inundative release may lead to a subsequent increase in their efficacy as biological control agents. Using the fruit fly parasitoid Diachasmimorpha krausii we tested this hypothesis in a series of associative learning experiments which involved the parasitoid, two host fruits (tomatoes and nectarine), and one host fly (Bactrocera ttyoni). In sequential Y-tube olfactometer studies, large field-cage studies, and then open field studies, naive wasps showed a consistent preference for nectarines over tomatoes. The preference for nectarines was retained, but not significantly increased, for wasps which had prior training exposure to nectarines. However, and again consistently at all three spatial scales, prior experience on tomatoes led to significantly increased attraction to this fruit by tomato-trained wasps, including those liberated freely in the environment. These results, showing consistency of learning at multiple spatial scales, gives confidence to the many laboratory-based learning studies which are extrapolated to the field without testing. The experiment also provides direct experimental support for the proposed practice of enhancing the quality of inundatively released parasitoids through associative learning.     

Identification of Soybean Genes Involved in Circadian Clock Mechanism and Photoperiodic Control of Flowering Time by In Silico Analyses

Glycine max is a photoperiodic short-day plant and the practical consequence of the response is latitude and sowing period limitations to commercial crops. Genetic and physiological studies using the model plants Arabidopsis thaliana and rice （Oryza sativa） have uncovered several genes and genetic pathways controlling the process, however information about the corresponding pathways in legumes is scarce. Data mining prediction methodologies, including multiple sequence alignment, phylogeneUc analysis, bioinformaUcs expression and sequence motif pattern identification, were used to identify soybean genes involved in day length perception and photoperiodic flowering induction. We have investigated approximately 330 000 sequences from open-access databases and have identified all bona fide central oscillator genes and circadian photoreceptors from A. thaliana in soybean sequence databases. We propose a working model for the photoperiodic control of flowering time in G. max, based on the identified key components. These results demonstrate the power of comparative genomics between model systems and crop species to elucidate the several aspects of plant physiology and metabolism.     

Self-/conspecific discrimination and superparasitism strategy in the ovicidal parasitoid Echthrodelphax fairchildii （Hymenoptera： Dryinidae）

Superparasitism in solitary parasitoids results in fatal competition between the immature parasitoids, and consequently only one individual can emerge. In the semisoli- tary ovicidal parasitoid Echthrodelphaxfairchildii （Hymenoptera： Dryinidae）, 2 adults can emerge under superparasitism with a short interval （〈24 h） between the first and second ovipositions. We determined the female parasitoid＇s behavioral responses under self- and conspecific superparasitism bouts with first-to-second oviposition intervals of 〈2 h. The self- and conspecific superparasitizing frequencies increased up to an oviposition interval of 0.75 h, with the former remaining lower than the latter, particularly for oviposition intervals of _〈0.25 h, suggesting the existence of self-/conspecific discrimination. The superparasitizing frequency plateaued for oviposition intervals of _〉0.75 h, with no dif- ference between self- and conspecific superparasitism. The ovicidal-probing frequency did not differ under self- and conspecific superparasitism, and was usually 〈20%. The females exhibited no preference for the oviposition side （i.e., ovipositing on the side with or without the first progeny） and almost always laid female eggs for any oviposition in- terval under self- and conspecific superparasitism. The sex ratio was not affected by the type of superparasitism, oviposition sides, or the occurrence of ovicidal probing. These observed results about the oviposition side, ovicidal probing, and sex ratios differed from the predictions obtained assuming that the females behave optimally. Possible reasons for the discrepancies are discussed： likely candidates include the high cost of selecting oviposition sides and ovicidal probing, and, for the sex ratio, the low frequency of encountering suitable hosts before superparasitism bouts.     

Phylogenetic Analysis of Brine Shrimp （Artemia） in China Using DNA Barcodinge

DNA barcoding is a powerful approach for characterizing species of organisms, especially those with almost identical morphological features, thereby helping to to establish phylogenetic relationships and reveal evolutionary histories. In this study, we chose a 648-bp segment of the mitochondrial gene, cytochrome c oxidase subunit 1 （COI）, as a standard barcode region to establish phylogenetic relationships among brine shrimp （Artemia） species from major habitats around the world and further focused on the biodiversity of Artemia species in China, especially in the Tibetan Plateau. Samples from five major salt lakes of the Tibetan Plateau located at altitudes over 4,000 m showed clear differences from other Artemia populations in China. We also observed two consistent amino acid changes, 153A/V and 183L/F, in the COI gene between the high and low altitude species in China. Moreover, indels in the COI sequence were identified in cyst and adult samples unique to the Co Qen population from the Tibetan Plateau, demonstrating the need for additional investigations of the mitochondrial genome among Tibetan Artemia populations.     

The role of herbivore‐ and plant‐related experiences in intraspecific host preference of a relatively specialized parasitoid

Parasitoids use odor cues from infested plants and herbivore hosts to locate their hosts. Specialist parasitoids of generalist herbivores are predicted to rely more on herbivorederived cues than plant-derived cues. Microplitis croceipes (Cresson)(Hymenoptera: Braconidae) is a relatively specialized larval endoparasitoid of Heliothis virescens (F.)(Lepidoptera: Noctuidae), which is a generalist herbivore on several crops including cotton and soybean. Using M. croceipes/H. virescens as a model system, we tested the following predictions about specialist parasitoids of generalist herbivores:(i) naive parasitoids will show innate responses to herbivore-emitted kairomones, regardless of host plant identity and (ii) herbivore-related experience will have a greater influence on intraspecific oviposition preference than plant-related experience. Inexperienced (naive) female M. croceipes did not discriminate between cotton-fed and soybean-fed H. virescens in oviposition choice tests, supporting our first prediction. Oviposition experience alone with either host group influenced subsequent oviposition preference while experience with infested plants alone did not elicit preference in M. croceipes, supporting our second prediction. Furthermore, associative learning of oviposition with host-damaged plants facilitated host location. I terestingly, naive parasitoids attacked more soybeathan cotton-fed host larvae in two-choice tests when a background of host-infested cotton odor was supplied, and vice versa. This suggests that plant volatiles may have created an olfactory contrast effect. We discussed ecological significance of the results and concluded that both plant- and herbivore-related experiences play important role in parasitoid host foraging.     

Association of aphid life stages using DNA sequences： A case study of tribe Eriosomatini （Hemiptera： Aphididae Pemphiginae）

Association of aphid life stages based on a portion of COI sequence was applied in Eriosomatini. Three aphid specimens, nos. 17496, 19265a, and 19265b collected on Gramineae roots all clustered with Tetraneura chinensis Mordvilko with strong support. The average pairwise p-distance among the four taxa was 0.001 （range, 0.000-0.002）, and that among all the ingroup taxa was 0.065 （range, 0.000-0.141）. This indicated that nos. 17496 and 19265 b were the secondary-host morphs of T. chinensis. In this paper the secondary host morph of T. chinensis is described for the first time. With the identification of more species＇ secondary-host morphs, aphids identification based on this morph will be made easily.     

Differential attraction of parasitoids in relation to specificity of kairomones from herbivores and their by-products

Infochemicals are used by foraging parasitoids in the host selection process from habitat preference until host recognition. Kairomones from the herbivore host plays a vital role in the attraction of parasitoids, particularly in the micro-habitat. Parasitoids are specifically attracted to their respective herbivore species even when different herbivores are present on the same plant. Chemicals emitted from different stages of host （eggs, larvae, pupae, adult）, host by-products （e.g., frass, exuviae, mandibular gland secretions, defense secretions etc.）, or intra-specific infochemicals （pheromones） can be main signals for the parasitoids. Parasitoids can differentiate between host and non-host, between different hosts and host stages by perceiving specific volatile and contact kairomones from the host itself, host along with its by-product, by-products alone or intra-specific infochemicals; of which frass （by-product） and intra-specific infochemicals are the most reported ones. Adult and larval parasitoids have been reported to be attracted to kairomones of their target stage or byproduct of their host. Pupal parasitoids have been found to utilize kairomones from the preceding host stage while egg parasitoids are known to exploit a variety of host infochemicals, for example, either from eggs themselves or other non-target host stages, especially adults and adult-related by-products. The kairomonal chemicals identified so far include various groups, but mainly hydrocarbons. A high degree of host specificity and host acceptance is important for the parasitoids as any mistake may result in the loss of fitness.     

Model Identification of a Micro Air Vehicle

This paper is focused on the model identification of a Micro Air Vehicle （MAV） in straight steady flight condition. The identification is based on input-output data collected from flight tests using both frequency and time dorrtain techniques. The vehicle is an in-house 40 cm wingspan airplane. Because of the complex coupled, multivariable and nonlinear dynamics of the aircraft, linear SISO structures for both the lateral and longitudinal models around a reference state were derived. The aim of the identification is to provide models that can be used in future development of control techniques for the MAV.     

Metabolic Engineering of Plant-derived (E)-β-farnesene Synthase Genes for a Novel Type of Aphid-resistant Genetically Modified Crop Plants

Aphids are major agricultural pests that cause significant yield losses of crop plants each year.Excessive dependence on insec-ticides for long-term aphid control is undesirable because of the development of insecticide resistance,the potential negative effects on non-target organisms and environmental pollution.Transgenic crops engineered for resistance to aphids via a non-toxic mode of action could be an efficient alternative strategy.(E)-β-Farnesene (EβF) synthases catalyze the formation of EβF,which for many pest aphids is the main component of the alarm pheromone involved in the chemical communication within these species.EβF can also be synthesized by certain plants but is then normally contaminated with inhibitory compounds.Engineering of crop plants capable of synthesizing and emitting EβF could cause repulsion of aphids and also the attraction of natural enemies that use EβF as a foraging cue,thus minimizing aphid infestation.In this review,the effects of aphids on host plants,plants' defenses against aphid herbivory and the recruitment of natural enemies for aphid control in an agricultural setting are briefly introduced.Furthermore,the plant-derived EβF synthase genes cloned to date along with their potential roles in generating novel aphid resistance via genetically modified approaches are discussed.     

DNA Barcode ITS Effectively Distinguishes the Medicinal Plant Boerhavia diffusa from Its Adulterants

Boerhavia diffusa (B. diffusa), also known as Punarnava, is an indigenous plant in India and an important component in traditional Indian medicine. The accurate identification and collection of this medicinal herb is vital to enhance the drug’s efficacy and biosafety. In this study, a DNA barcoding technique has been applied to identify and distinguish B. diffusa from its closely-related species. The phylogenetic analysis was carried out for the four species of Boerhavia using barcode candidates including nuclear ribosomal DNA regions ITS, ITS1, ITS2 and the chloroplast plastid gene psbA-trnH. Sequence alignment revealed 26% polymorphic sites in ITS, 30% in ITS1, 16% in ITS2 and 6% in psbA-trnH, respectively. Additionally, a phylogenetic tree was constructed for 15 species using ITS sequences which clearly distinguished B. diffusa from the other species. The ITS1 demonstrates a higher transition/transversion ratio, percentage of variation and pairwise distance which differentiate B. diffusa from other species of Boerhavia. Our study revealed that ITS and ITS1 could be used as potential candidate regions for identifying B. diffusa and for authenticating its herbal products.