Aphid Growth Research Articles

Seed inoculations with entomopathogenic fungi affect aphid populations coinciding with modulation of plant secondary metabolite profiles across plant families.

Entomopathogenic fungi (EPF) can display a plant-associated lifestyle as endophytes. Seed application of EPF can affect insect herbivory above ground, but the mechanisms behind this are not documented. Here we applied three EPF isolates, Beauveria bassiana, Metarhizium brunneum and M.robertsii, as seed inoculation of wheat and bean, and evaluated the effects on population growth of aphids, Rhopalosiphum padi and Aphis fabae, respectively. In wheat and bean leaves, we quantified benzoxazinoids and flavonoids, respectively, in response to EPF inoculation and aphid infestation to elucidate the role of specific plant secondary metabolites (PSMs) in plant-fungus-herbivore interactions. Inoculations of wheat and bean with M.robertsii and B.bassiana reduced aphid populations compared with control treatments, whereas M.brunneum unexpectedly increased the populations of both aphids. Concentrations of the majority of PSMs were differentially altered in EPF-treated plants infested with aphids. Changes in aphid numbers were associated with PSMs regulation rather than EPF endophytic colonisation capacity. This study links the effects of EPF seed inoculations against aphids with unique PSM accumulation patterns in planta. The understanding of PSM regulation in tri-trophic interactions is important for the future development of EPF for pest management.

Constitutive expression of an endogenous sugar transporter gene SWEET11 in Indian mustard (Brassica juncea) and its effect thereof on mustard aphids

One of the major oil yielding crops Indian mustard [Brassica juncea (L.) Czern. & Coss.] is highly susceptible to mustard aphid, a hemipteran sap sucking insect-pest. Leaf-transcriptome of mustard treated with different aphid species as host and non-host revealed variable expression of three sugar transporter genes. One of these transporters BjSWEET11 was constitutively expressed under a CaMV 35S promoter in B. juncea through Agrobacterium-mediated plant transformation. The transgenic plants after requisite molecular analysis for the presence and expression of the introduced gene were assayed for their deterring effects on the infestation by mustard aphid (Lipaphis erysimi). Attenuating effect of the enhanced BjSWEET11 expression on multiplication and population growth of mustard aphids demonstrated likely involvement of this transporter in endogenous plant defense mechanism.

Effect of silicon on aphid populations and wheat yield in Minas Gerais, Brazil

The area cultivated with wheat has been increasing in the savannahs of the state of Minas Gerais, Brazil. Aphids are usually one of the main pests of wheat in many regions of the world; however, little is known about the aphid population in this new environment. The southern region of Brazil, the main wheat production area, has had several problems as a result of aphids, but aphid populations and the resulting impact on wheat production have not been investigated in these new crop production areas. Understanding control strategies to manage this insect could be essential for the “Cerrado” wheat that is grown in this area. The application of silicon (Si) has the potential to reduce the population growth of wheat aphids; however no field studies have been reported. Hence, we evaluated the effect of Si fertilization via soil application on the aphid populations and species composition and on yield components of wheat in three locations in Minas Gerais; the experiment was repeated simultaneously in Uberlândia, at the experimental areas of UFU and IFTM, and in Montes Claros, at the experimental area of UFMG, using the cultivars BRS 264 and BRS 394. The aphids first appeared just before wheat earing; they were then sampled six times over the course of the study, seven days apart, starting from 45 days after sowing. The aphid species Sitobion avenae (Fabricius), Schizaphis graminum (Rondani), and Rhopalosiphum padi (Linnaeus) were observed in all three locations; S. avenae was the dominant species in all locations. The experimental area of UFU had the highest number of S. avenae aphids per tiller for both cultivars, while UFMG had the lowest populations. Aphid populations and wheat yield components were not affected by soil Si fertilization. There was no difference in yield as a result of location or cultivar, but the location UFU and the cultivar BRS 394 had the greatest average hectoliter weight.

Effects of drought and mycorrhiza on wheat and aphid infestation.

The impacts of climate change on worldwide crop production become increasingly severe. Thus, sustainable enhancements of agricultural production are needed. The present study investigated the effects of drought and arbuscular mycorrhizal fungi on wheat plants (Triticum aestivum) and their interaction with aphids. Considering predicted climate change scenarios, wheat plants were exposed to well‐watered conditions, continuous drought (CD), or pulsed (PD) drought and plants were grown without (NM) or with mycorrhizal (AM) fungi. Ear biomass and harvest index were evaluated when grains were produced. Moreover, drought‐ and mycorrhiza‐induced changes in the amino acid composition of leaf phloem exudates were studied and the population growth and survival of Sitobion avenae aphids on those plants measured. Wheat plants responded differently toward the irrigation treatments. Under drought stress, ear biomass was reduced, while AM resulted in an enhanced harvest index. In phloem exudates especially, relative concentrations of the osmoprotectant proline were modulated by drought. Aphid population size was influenced by the interaction of drought and mycorrhiza treatment. This study emphasizes the pronounced influence of irrigation frequency on plant performance and indicates positive contributions of AM that may be relevant for agriculture.

Establishment of the entomopathogenic fungus Beauveria bassiana as an endophyte in Capsicum annuum and its effects on the aphid pest Myzus persicae (Homoptera: Aphididae)

Introduction: Entomopathogenic fungi have been used as biological control agents of insect pests and have demonstrated a promising ability to colonize as endophytes a wide range of plant species. Objective: The aims of this study were to evaluate, in pepper plants, the most effective Beauveria bassiana inoculation techniques. In order to evaluate the presence of natural endophytes and its interaction with B. bassiana. Also to assess the effect of B. bassiana on the aphid Myzus persicae pepper leaf feeding preference and growth. Methods: Three inoculation techniques were evaluated: leaf spraying, seed immersion and root dipping. The pepper plants were inoculated with a conidia suspension adjusted to 1×108 conidia/ml. The presence of B. bassiana in the seedlings was evaluated at 7, 15 and 28 days after inoculation. Results: We found significant statistical differences between inoculation techniques. Foliar spraying showed the highest B. bassiana colonization frequency. The natural endophytes presented higher presence in the treatments in which B. bassiana had a low presence. This might indicate the occurrence of antifungal activity that interferes with the establishment of the entomopathogen in pepper tissues. We did not find statistical differences between inoculated and control pepper leaves with regard to the mortality and reproduction of the aphid pest M. persicae. However, the inoculation with B. bassiana showed a tendency to increase the mortality of adults and to decrease the offspring (nymphs). We did not find significant differences in the feeding preference between inoculated and control leaves, although there was a higher number of individuals on control leaves compared to those inoculated. Conclusions: The strain B. bassiana LPSC 1067 was established effectively as an endophyte in the pepper tissues. The most effective inoculation technique was leaf spraying. We did not find differences of statistical significance with regard to the mortality and reproduction of the aphid pest M. persicae. However, the inoculation with B. bassiana showed a tendency to increase the mortality of adults and to decrease the offspring (nymphs). Future studies evaluating the indirect effects of endophytic entomopathogens on both plants and herbivorous insects are needed to further explore their potential use in the management of insect pests.

Simultaneous Increase in CO2 and Temperature Alters Wheat Growth and Aphid Performance Differently Depending on Virus Infection.

Climate change impacts crop production, pest and disease pressure, yield stability, and, therefore, food security. In order to understand how climate and atmospheric change factors affect trophic interactions in agriculture, we evaluated the combined effect of elevated carbon dioxide (CO2) and temperature on the interactions among wheat (Triticum aestivum L.), Barley yellow dwarf virus species PAV (BYDV-PAV) and its vector, the bird cherry-oat aphid (Rhopalosiphum padi L.). Plant traits and aphid biological parameters were examined under two climate and atmospheric scenarios, current (ambient CO2 and temperature = 400 ppm and 20 °C), and future predicted (elevated CO2 and temperature = 800 ppm and 22 °C), on non-infected and BYDV-PAV-infected plants. Our results show that combined elevated CO2 and temperature increased plant growth, biomass, and carbon to nitrogen (C:N) ratio, which in turn significantly decreased aphid fecundity and development time. However, virus infection reduced chlorophyll content, biomass, wheat growth and C:N ratio, significantly increased R. padi fecundity and development time. Regardless of virus infection, aphid growth rates remained unchanged under simulated future conditions. Therefore, as R. padi is currently a principal pest in temperate cereal crops worldwide, mainly due to its role as a plant virus vector, it will likely continue to have significant economic importance. Furthermore, an earlier and more distinct virus symptomatology was highlighted under the future predicted scenario, with consequences on virus transmission, disease epidemiology and, thus, wheat yield and quality. These research findings emphasize the complexity of plant–vector–virus interactions expected under future climate and their implications for plant disease and pest incidence in food crops.

Aphid growth and reproduction on plants with altered sterol profiles: Novel insights using Arabidopsis mutant and overexpression lines

Sterols are essential membrane components and are critical for many physiological processes in all eukaryotes. Insects and other arthropods are sterol auxotrophs that typically rely on a dietary source of sterols. Herbivorous insects generally obtain sterols from plants and then metabolize them into cholesterol, the dominant sterol in most insects. However, there is significant variation in phytosterol structure, and not all phytosterols are equally suitable for insects. In the current study, we used seven Arabidopsis thaliana lines that display altered sterol profiles due to mutations in the sterol biosynthetic pathway or to overexpression of key enzymes of the pathway, and investigated how plant sterol profiles affected green peach aphid (Myzus persicae) growth and reproduction. We also characterized the sterol profile of aphids reared on these Arabidopsis genotypes. Aphids on two mutant lines (14R/fk and ste1-1) that accumulated biosynthetic sterol intermediates (Δ8,14-sterols, and Δ7-sterols, respectively) all showed significantly reduced growth and reproduction. Aphids on SMT2COSUP plants (which have decreased β-sitosterol but increased campesterol) also displayed significantly reduced growth and reproduction. However, aphids on SMT2OE plants (which have increased β-sitosterol but decreased campesterol) performed similarly to aphids on wild-type plants. Finally, Arabidopsis plants that had an overproduction of sterols (CD-HMGROE) or decreased sterol esters (psat1-2) had no impact on aphid performance. Two noteworthy results come from the aphid sterol profile study. First, β-sitosterol, cholesterol and stigmasterol were recovered in all aphids. Second, we did not detect Δ8,14-sterols in aphids reared on 14R/fk plants. We discuss the implications of our findings, including how aphid sterol content does not appear to reflect plant leaf sterol profiles. We also discuss the potential of modifying plant sterol profiles to control insect herbivore pests, including aphids.

An ERF transcription factor enhances plant resistance to Myzus persicae and Spodoptera litura

Aphids are sap-sucking insects and are pests that cause substantial damage to many crops worldwide. Spodoptera litura is a leaf-chewing insect and poses a severe threat to many species of vegetable and cotton plants. In this paper, we studied an ethylene-responsive factor (ERF) that enhances plant resistance to sap-sucking and leaf-chewing insects. ERF11-like was obtained from Chinese cabbage via reverse transcription-polymerase chain reaction and was termed BrERF11b. The putative protein encoded by the BrERF11b gene includes 168 amino acid residues and contains an EAR motif. The plasmid pBI121-BrERF11b was constructed and transformed into tobacco plants (Nicotiana tabacum cv. K326 and N. benthamiana) by the Agrobacterium-mediated transformation method. The function of the BrERF11b gene in the resistance of the transgenic plants to Myzus persicae and S. litura was assayed. The results showed that the weights of the S. litura larvae fed the transgenic plant line were significantly reduced from 28 to 76% compared to those of the S. litura larvae fed the control plants (wild type), and the transgenic plant line KLine12 significantly reduced the survival rate of S. litura by 62.5%. The colony growth of the apteral aphids fed the transgenic plant line was significantly reduced from 22.5 to 63.4% compared to that of the apteral aphids fed the control plants. Compared to control plants, the transgenic plant line significantly reduced the survival rate of the aphids from 46 to 55%. These results first indicate that the BrERF11b gene significantly enhances plant resistance to S. litura and M. persicae.

Temperature Dependent Development of Sugarcane Aphids Melanaphis Sacchari, (Hemiptera: Aphididae) on Three Different Host Plants with Estimates of the Lower and Upper Threshold for Fecundity

Abstract The sugarcane aphid, Melanaphis sacchari (Zehntner) is a serious economic threat to grain sorghum across the U.S. sorghum belt. It can develop on multiple grass hosts but only appears to survive winter temperatures in Texas near the Mexican border, Florida and Louisiana. Because survival and reproduction of aphids is dependent on access to appropriate nutrition and temperatures at which metabolic processes are maintained, we evaluated the growth, reproduction and survival of sugarcane aphids at constant temperatures (5°C,10°C,15°C,20°C,25°C,30°C,35°C) on three known hosts, sorghum, Johnsongrass, and Columbus grass. Longevity, fecundity, number of female nymphs/d, reproductive period in d, and intrinsic rate of increase were measured at 24 h intervals. At temperatures below 10°C and above 30°C, reproduction did not occur on any of the hosts. Longevity was maximal at 15oC and thereafter decreased with increasing temperatures. The intrinsic rate of increase was highest between 15oC and 25°C on all host plants, while maximum fecundity differed by host plant and was greatest on sorghum. For aphids feeding on sorghum, the Weibull and Natural models were used to estimate lower and upper thresholds for development based on daily fecundity. The lower threshold for fecundity was 9oC, while the upper threshold for fecundity was 32oC. These results suggest that sugarcane aphid can use alternate hosts for survival and reproduction, but both low and high temperatures limit its reproductive capacity. Higher temperatures may trigger dispersal, while lower temperatures should limit sugarcane aphid fecundity and survival in most of the US. Keywords Growth; Host Plants; Reproduction; SugarcaneAphid; Temperature Threshold

Quantitative trait locus for resistance to the aphid Rhopalosiphum padi L. in barley (Hordeum vulgare L.) is not linked with a genomic region for gramine concentration

Gramine is an indole alkaloid found in certain grass species. Results of previous studies have diverged as to whether this compound might cause resistance to aphids or not. In a breeding program aiming to introduce resistance to the cereal pest Rhopalosiphum padi L. in barley, a cultivar has been crossed with the progenitor of cultivated barley, Hordeum vulgare ssp. spontaneum, and an F1-derived population of doubled haploid (DH) lines was screened both for seedling gramine concentration and resistance to R. padi. The resistance was measured as individual aphid growth in the laboratory. The present study aims to determine if there is a genetic relationship between aphid growth retardation and gramine concentration. To do so, the lines were genotyped with a 384 SNP oligonucleotide pool assay and QTL analyses were performed for both traits. A previously identified aphid resistance locus on the distal part of chromosome 2HS was thereby confirmed, with resistance inherited from H. v. ssp. spontaneum, whereas one or more QTL for gramine concentration were potentially indicated on chromosome 3H, thus corroborating that the two traits are not linked genetically.

Intercropping impacts the host location behaviour and population growth of aphids

AbstractIncreasing intrafield plant diversity has been shown to regulate pest populations in various agroecosystems. Among the suggested mechanisms for this bottom‐up pest control, the disruptive crop hypothesis states that herbivores' abilities to locate and colonize their host plants are reduced by the presence of non‐host plants. Under laboratory conditions, we evaluated how intercropping wheat and legumes modifies the behaviour of apterous cereal aphids,Sitobion avenae(Fabricius) (Hemiptera: Aphididae), in terms of host plant location and population growth. We compared two intercropping systems – soft winter wheat,Triticum aestivumL. (Poaceae), associated with winter pea,Pisum sativumL., or with white clover,Trifolium repensL. (both Fabaceae) – and sole stands of soft winter wheat. Aphids needed more time to locate their wheat host plant and then spent less time on wheat when it was intercropped with clover. At the population level, and accounting for host plant biomass, only intercropping wheat with clover significantly reduced aphid densities on wheat, as this was particularly disruptive toS. avenaebehaviour and population growth.Our laboratory study points out that the species used as non‐host plants and their density are important parameters that should be taken into account in field studies on intercropping systems.

Transcriptional and Chemical Changes in Soybean Leaves in Response to Long-Term Aphid Colonization.

Soybean aphids (Aphis glycines Matsumura) are specialized insects that feed on soybean (Glycine max) phloem sap. Transcriptome analyses have shown that resistant soybean plants mount a fast response that limits aphid feeding and population growth. Conversely, defense responses in susceptible plants are slower and it is hypothesized that aphids block effective defenses in the compatible interaction. Unlike other pests, aphids can colonize plants for long periods of time; yet the effect on the plant transcriptome after long-term aphid feeding has not been analyzed for any plant–aphid interaction. We analyzed the susceptible and resistant (Rag1) transcriptome response to aphid feeding in soybean plants colonized by aphids (biotype 1) for 21 days. We found a reduced resistant response and a low level of aphid growth on Rag1 plants, while susceptible plants showed a strong response consistent with pattern-triggered immunity. GO-term analyses identified chitin regulation as one of the most overrepresented classes of genes, suggesting that chitin could be one of the hemipteran-associated molecular pattern that triggers this defense response. Transcriptome analyses also indicated the phenylpropanoid pathway, specifically isoflavonoid biosynthesis, was induced in susceptible plants in response to long-term aphid feeding. Metabolite analyses corroborated this finding. Aphid-treated susceptible plants accumulated daidzein, formononetin, and genistein, although glyceollins were present at low levels in these plants. Choice experiments indicated that daidzein may have a deterrent effect on aphid feeding. Mass spectrometry imaging showed these isoflavones accumulate likely in the mesophyll cells or epidermis and are absent from the vasculature, suggesting that isoflavones are part of a non-phloem defense response that can reduce aphid feeding. While it is likely that aphid can initially block defense responses in compatible interactions, it appears that susceptible soybean plants can eventually mount an effective defense in response to long-term soybean aphid colonization.

Introgression of resistance to Rhopalosiphum padi L. from wild barley into cultivated barley facilitated by doubled haploid and molecular marker techniques

Key messageLong-term pre-breeding using Hordeum vulgare ssp. spontaneum as a donor of bird cherry-oat aphid resistance has resulted in agronomically improved resistance sources of barley along with easy-to-use molecular markers.Bird cherry-oat aphid (Rhopalosiphum padi L.) is a pest and a virus vector in barley to which there are no bred-resistant cultivars. The present study describes how resistance from Hordeum vulgare ssp. spontaneum has been introgressed in cultivated barley via five successive crosses with the same cultivar Lina (BC) and in parallel with other more modern barley cultivars. Most of the selections for resistance are based on measurements of individual aphid growth in the laboratory. This very slow phenotyping method has been complemented by molecular marker evaluation and application in part of the breeding material. Doubled haploid production in each generation has been crucial for more precise selection of lines with the quantitatively expressed resistance. A field trial of selected “BC3”-generation lines essentially confirmed the laboratory results, so did genotyping of the whole pedigree of parents and selected “BC2” and “BC4” offspring lines. The Infinium iSelect 50 K SNP assay confirmed relationships between lines and discerned several new markers for a resistance QTL on chromosome 2H.

Additive effects of plant chemotype, mutualistic ants and predators on aphid performance and survival

Abstract Cascading effects in ecological systems acting across three or more trophic levels can be either of a resource‐based (bottom‐up) or natural enemy‐based (top‐down) nature. But, due to their complexity, these effects are often considered separately and their relative strength, acting simultaneously, remains unknown. In a semi‐natural field experiment using tansy (Tanacetum vulgare L.) and the specialised tansy‐aphid Metopeurum fuscoviride Stroyan as a model system, we compared the effects of four distinct plant chemotypes (i.e., bottom‐up), defined by the bouquet of their volatile terpenoids, on aphid population dynamics by manipulating the presence/absence of mutualistic ants and presence/absence of naturally occurring predators (i.e., top‐down). Predators reduced aphid abundance and colony survival but did not reduce initial growth rate due to a time‐lag until predators arrived on the plants. Ants directly benefited initial aphid growth rates and abundance, even in the absence of predators, but not the number of days an aphid colony persisted on the plant. Plant chemotype directly affected aphid growth rate and final abundances across the different plants and indirectly affected the abundances of tending ants and predators through effects on aphids. We found that tending ants were more abundant on one plant chemotype. Although ant abundance did not affect aphid population development, it became clear that ants had a preference towards aphids on certain chemotypes. However, a higher number of predators led to a lower number of aphids. The results confirm the importance of plant chemical variation, acting through multiple effects on many species in arthropod communities, and support results from field studies. In a natural population, with a diverse selection of host‐plant variants, aphid populations and their interacting species can therefore be structured at the level of an individual plant. Specialist aphids on patchily distributed host plants can exhibit metacommunity dynamics at very local scales. Plant within‐species variation within a local population is often ignored in metacommunity ecology, yet our work shows that this can have strong effects on insect–ant–natural enemy dynamics, and therefore, future research should incorporate this into current theory and experimental studies. A plain language summary is available for this article.

Landscape structure alters the abundance and species composition of early-season aphid populations in wheat fields

Agricultural landscape composition is reported to have effects on the occurrence of natural enemies in fields, but the responses of herbivorous pests to landscape features have rarely been studied. Our previous landscape-level study in northern China found that natural enemies had no significant effects on the population growth of wheat aphids at the colonization stage. Hence, we hypothesised that the initial aphid population in wheat fields may largely depend on immigration events from other habitats. In this study, we investigated the effects of landscape pattern on wheat aphid abundance and species composition at the colonization stage by surveying population densities of different aphid species along a landscape gradient. We found that noncrop habitats such as woodlots, fallow lands and vegetation around dwellings or wetlands in the landscape all had positive correlations with aphid abundance in wheat fields because they provided a source for aphid colonization. More specifically, the proportion of woodlots, fallow lands, dwellings, and other crops increased the abundance of Rhopalosiphum padi (L.), and the existence of water and dwellings in an agricultural landscape facilitated the occurrence of Sitobion avenae (Fabricius). Likewise, the abundance of Schizaphis graminum (Rondani) in wheat fields was found to be significantly promoted by the presence of water. The habitats around water and dwellings usually provide the overwintering sites for the aphids. Furthermore, wheat production acreage had a significant negative correlation with the abundance of R. padi, S. avenae and S. graminum. Landscape characteristics had a significant effect on the species composition of wheat aphids. Our study suggests that noncrop habitats in a landscape enhance aphid occurrence at the population colonization stage, and differences in overwintering host plants among aphid species may be responsible for the differing responses of the abundance of different aphids to landscape variables, which greatly altered aphid population composition across different landscapes. These results highlight the need for taking landscape effects on the pest itself into consideration when designing landscape-level pest management strategies.

Bacteria and Competing Herbivores Weaken Top-Down and Bottom-Up Aphid Suppression.

Herbivore suppression is mediated by both plant defenses and predators. In turn, plant defenses are impacted by soil fertility and interactions with soil bacteria. Measuring the relative importance of nutritional and microbial drivers of herbivore resistance has proven problematic, in part because it is difficult to manipulate soil-bacterial community composition. Here, we exploit variation in soil fertility and microbial biodiversity across 20 farms to untangle suppression of aphids (Brevicoryne brassicae) through bottom–up and top–down channels. We planted Brassica oleracea plants in soil from each farm, manipulated single and dual infestations of aphids alone or with caterpillars (Pieris rapae), and exposed aphids to parasitoid wasps (Diaeretiella rapae) in the open field. We then used multi-model inference to identify the strongest soil-based predictors of herbivore growth and parasitism. We found that densities of Bacillus spp., a genus known to include plant-growth-promoting rhizobacteria, negatively correlated with aphid suppression by specialist parasitoids. Aphid parasitism also was disrupted on plants that had caterpillar damage, compared to plants attacked only by aphids. Relative abundance of Pseudomonas spp. bacteria correlated with higher aphid growth, although this appeared to be a direct effect, as aphid parasitism was not associated with this group of bacteria. Non-pathogenic soil bacteria are often shown to deliver benefits to plants, improving plant nutrition and the deployment of anti-herbivore defenses. However, our results suggest that these plant growth-promoting bacteria may also indirectly weaken top–down aphid suppression by parasitoids and directly improve aphid performance. Against a background of varying soil fertility, microbial biodiversity, competing herbivores, and natural enemies, we found that effects of non-pathogenic soil microbes on aphid growth outweighed those of nutritional factors. Therefore, predictions about the strength of plant defenses along resource gradients must be expanded to include microbial associates.

MTOR Complex 1 Implicated in Aphid/Buchnera Host/Symbiont Integration.

Obligate nutritional endosymbioses are arguably the most intimate of all interspecific associations. While many insect nutritional endosymbioses are well studied, a full picture of how two disparate organisms, a bacterial endosymbiont and a eukaryotic host, are integrated is still lacking. The mTOR pathway is known to integrate nutritional conditions with cell growth and survival in eukaryotes. Characterization and localization of amino acid transporters in aphids suggest the mTOR pathway as a point of integration between an aphid host and its amino acid-provisioning endosymbiont Buchnera aphidicola. The mTOR pathway is unannotated in aphids and unstudied in any nutritional endosymbiosis. We annotated mTOR pathway genes in two aphid species, Acyrthosiphon pisum and Myzus persicae, using both BLASTp searches and Hidden Markov Models. Using previously collected RNAseq data we constructed new reference transcriptomes for bacteriocyte, gut, and whole insect tissue for three lines of M. persicae. Annotation of the mTOR pathway identified homologs of all known invertebrate mTOR genes in both aphid species with some duplications. Differential expression analysis showed that genes specific to the amino acid-sensitive mTOR Complex 1 were more highly expressed in bacteriocytes than genes specific to the amino acid-insensitive mTOR Complex 2. Almost all mTOR genes involved in sensing amino acids showed higher expression in bacteriocytes than in whole insect tissue. When compared to gut, the putative glutamine/arginine sensing transporter ACYPI000333, an ortholog of SLC38A9, showed 6.5 times higher expression in bacteriocytes. Our results suggest that the mTOR pathway may be functionally important in mediating integration of Buchnera into aphid growth and reproduction.

Impact of the parasitoid Aphelinus certus on soybean aphid populations

Aphelinus certus Yasnosh (Hymenoptera: Aphelinidae) is an accidentally introduced parasitoid of the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae) in North America and it has become one of the most common natural enemies of soybean aphids in its adventive range. It is unclear, however, if increased prevalence of A. certus has resulted in increased biological control. We conducted an exclusion-cage experiment designed to isolate the impact of parasitoids from that of other resident natural enemies (mainly predators) of the soybean aphid. We found that A. certus greatly outnumbered all other soybean aphid parasitoids, and that it significantly reduced soybean aphid populations over a time span of less than two weeks compared to controls. Moreover, parasitoids alone resulted in aphid densities that were statistically equivalent to the combined effect of predators and parasitoids. Across all treatment cages, there was a significant negative association between parasitism rate and aphid population growth, with predicted zero aphid growth occurring at a parasitism rate of 42.2%.

Drought and soil fertility modify fertilization effects on aphid performance in wheat

Agricultural intensification and climate change are expected to affect pest performance through excessive inputs of chemical fertilizers and increased probability of extreme drought events. Potential interactive effects of fertilization and water availability on aboveground pest performance may depend on soil fertility because of its effect on nutrient availability. In a greenhouse experiment, we examined the effects of inorganic fertilization on the performance of the grain aphid (Sitobion avenae, F.), an important pest of wheat, under different conditions of soil fertility and water availability. We found soil fertility and water availability to influence the positive effects of inorganic fertilizers on aphid growth, i.e. fertilization promoted faster aphid development time and higher fecundity and biomass under low fertility and under well-watered conditions. Moreover, although increased soil fertility favored aphid growth under well-watered conditions, it simultaneously sustained plant development. The current practices promoting soil fertility do not have direct negative consequence on crop protection under conventional cropping systems.

Expression of Pinellia pedatisecta Lectin Gene in Transgenic Wheat Enhances Resistance to Wheat Aphids.

Wheat aphids are major pests during the seed filling stage of wheat. Plant lectins are toxic to sap-sucking pests such as wheat aphids. In this study, Pinellia pedatisecta agglutinin (ppa), a gene encoding mannose binding lectin, was cloned, and it shared 92.69% nucleotide similarity and 94% amino acid similarity with Pinellia ternata agglutinin (pta). The ppa gene, driven by the constitutive and phloem-specific ribulose bisphosphate carboxylase small subunit gene (rbcs) promoter in pBAC-rbcs-ppa expression vector, was transferred into the wheat cultivar Baofeng104 (BF104) by particle bombardment transformation. Fifty-four T0 transgenic plants were generated. The inheritance and expression of the ppa gene were confirmed by PCR and RT-PCR analysis respectively, and seven homozygous transgenic lines were obtained. An aphid bioassay on detached leaf segments revealed that seven ppa transgenic wheat lines had lower aphid growth rates and higher inhibition rates than BF104. Furthermore, two-year aphid bioassays in isolated fields showed that aphid numbers per tiller of transgenic lines were significantly decreased, compared with wild type BF104. Therefore, ppa could be a strong biotechnological candidate to produce aphid-resistant wheat.