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Background Genetic resistance of soybean [ Glycine max (L.) Merr] against Aphis glycines provides effective management of this invasive pest, though the underlying molecular mechanisms are largely unknown. This study aimed to investigate genome-wide changes in gene expressions of soybean near-isogenic lines (NILs) either with the Rag 5 allele for resistance or the rag 5 allele for susceptibility to the aphid following infestation with soybean aphid biotype 2. Results The resistant (R)-NIL responded more rapidly to aphid infestation than the susceptible (S)-NIL, with differential expressions of 2496 genes during first 12 h of infestation (hai), compared to the aphid-free control. Although the majority of the differentially expressed genes (DEGs) in the R-NIL also responded to aphid infestation in S-NIL, overall the response time was longer and/or the magnitude of change was smaller in the S-NIL. In addition, 915 DEGs in R-NIL continued to be regulated at all time points (0, 6, 12, and 48 hai), while only 20 DEGs did so in S-NIL. Enriched gene ontology of the 2496 DEGs involved in plant defense responses including primary metabolite catalysis, oxidative stress reduction, and phytohormone-related signaling. By comparing R- vs. S-NIL, a total of 556 DEGs were identified. Of the 13 genes annotated in a 120-kb window of the Rag 5 locus, two genes (Glyma.13 g190200 and Glyma.13 g190600) were differentially expressed (upregulated in S- or R-NIL), and another gene (Glyma.13 g190500) was induced up to 4-fold in the R-NIL at 6 and 12 h following aphid infestation. Conclusions This study strengthens our understanding of the defense dynamics in compatible and incompatible interactions of soybean and soybean aphid biotype 2. Several DEGs (e.g., Glyma.13 g190200, Glyma.13 g190500, and Glyma.13 g190600) near the Rag 5 locus are strong candidate genes for further investigations.

Host plant resistance to the soybean aphid, Aphis glycines Matsumura, is an effective means of controlling populations of this introduced pest species in the United States. Rag (Resistance to Aphis glycines) genes identified in soybean germplasm have been incorporated into commercial cultivars, but differential responses by soybean aphid biotypes to the Rag genes have made understanding mechanisms underlying resistance associated with Rag genes increasingly important. We compared the behavior of biotype 2 aphids on the resistant soybean line PI243540, which is a source of Rag2, and the susceptible cultivar Wyandot. Scanning electron microscopy revealed that the abaxial surface of leaves from resistant plants had a higher density of both long and glandular trichomes, which might repel aphids, on veins. Time-lapse animation also suggested a repellent effect of resistant plants on aphids. However, electropenatography (EPG) indicated that the time to first probe did not differ between aphids feeding on the resistant and susceptible lines. EPG also indicated that fewer aphids feeding on resistant plants reached the phloem, and the time before reaching the phloem was much longer relative to susceptible soybean. For aphids that reached the phloem, there was no difference in either number of feedings or their duration in phloem. However, aphids feeding on resistant soybean had fewer prolonged phases of active salivation (E1) and many more pathway activities and non-probing intervals. Together, the feeding behavior of aphids suggested that Rag2 resistance has strong antixenosis effects, in addition to previously reported antibiosis, and was associated with epidermal and mesophyll tissues.

The population dynamics of the soybean aphid (Aphis glycines Matsumura) was studied over a 12-yr period (2004–2015) from archive and field data collected in the Montérégie area of Quebec (Canada). As observed in the United States, a 2-yr oscillation cycle was observed from 2005 to 2011 in Quebec, with high infestations during odd years, while the opposite was found in 2014 and 2015. A broader pattern could also be observed, with high infestation in two consecutive years every 10 yr. In addition, the infestation intensity observed in high infestation years decreases throughout the years, which questions the evolution of the oscillation cycle in the future.

The mutualism between legumes and nitrogen-fixing soil bacteria (rhizobia) is a key feature of many ecological and agricultural systems, yet little is known about how this relationship affects aboveground interactions between plants and herbivores. We investigated the effects of the rhizobia mutualism on the abundance of a specialized legume herbivore on soybean plants. In a field experiment, soybean aphid (Aphis glycines) abundances were measured on plants (Glycine max) that were either (1) treated with a commercial rhizobial inoculant, (2) associating solely with naturally occurring rhizobia, or (3) given nitrogen fertilizer. Plants associating with naturally occurring rhizobia strains exhibited lower aphid population densities compared to those inoculated with a commercial rhizobial preparation or given nitrogen fertilizer. Genetic analyses of rhizobia isolates cultured from field plants revealed that the commercial rhizobia strains were phylogenetically distinct from naturally occurring strains. Plant size, leaf nitrogen concentration, and nodulation density were similar among rhizobia-associated treatments and did not explain the observed differences in aphid abundance. Our results demonstrate that plant-rhizobia interactions influence plant resistance to insect herbivores and that some rhizobia strains confer greater resistance to their mutualist partners than do others.

Very little is known about how spatial effects influence invasive species throughout the invasion sequence. We propose here two mechanisms to explain the changes in spatial effects throughout the stages of invasion, using the soybean aphid (Aphis glycines) as a model. First, the “hierarchical spatial effect” hypothesis, based on a change in the relative importance of the spatial scales throughout the invasion process, with main effect at broad scale during the first years of invasion, and main effect at local scale during the subsequent years. Second, the “host-switching spatial effect” hypothesis, stating that the spatial effect is driven by a switch in the effect of the host/habitat throughout the invasion process, from effect of main summer host/habitat during the first years of invasion to effect of overwintering host/habitat during the subsequent years. Data from governmental archives and field samplings enabled to investigate the spatial effects on aphid density at three scales (regional, landscape, local) during a 7 year period (2006–2012). Our results demonstrate that the hierarchical spatial effect hypothesis is not an adequate model for the soybean aphid, aphid density being more affected by landscape-scale factors irrespective of years. In contrast, our results are in accordance with the host-switching spatial hypothesis, with positive effect of the main summer host/habitat (soybean) during the first steps of invasion (2006–2008), followed by a positive effect of overwintering habitats (buckthorn, woodland) during the subsequent years (2010–2012). Overall, investigating these hypotheses in other systems would determine whether the same tendency is observed for other invasive species.

RNA interference (RNAi) has been recognized as a novel and safe strategy in pest management due to its high sequence-dependent specificity. However, the existing dsRNA delivery methods largely restrict the application of the RNAi-based pest management strategy; thus, we previously constructed a nanocarrier-based transdermal dsRNA delivery system on the soybean aphid Aphis glycines with the help of nanocarrier and detergent. In the current study, we improved our transdermal dsRNA delivery system with a smaller and cheaper nanocarrier to investigate the efficacy of spraying aphid-infested soybean seedlings to apply our RNA pesticide. A dsRNA/nanocarrier/detergent formulation was performed, and the dsRNA could penetrate the aphid body wall within 4 h with the help of nanocarrier through the topical application. Four potential RNAi target genes ( TREH , ATPD , ATPE and CHS1 ) were selected and cloned, and their dsRNA fragments were synthesized and tested through the transdermal dsRNA delivery system. The delivered dsRNA efficiently silenced the target gene expression with the knockdown effects ranging from 86.86 to 58.87% and resulted in a high mortality up to 81.67% (dsATPD + dsATPE) through the topical application, when through the spray method, with the highest percent mortality of 78.50% (dsATPD + dsCHS1). Our novel transdermal dsRNA delivery system not only provides a powerful tool for gene functional analysis in laboratory, but also shows a great potential for the pest management in the field, which will promote the practice and development of RNAi-based pest management.

Terrestrial plants can harbor endophytic fungi that may induce changes in plant physiology that in turn affect interactions with herbivorous insects. We evaluated whether the application of entomopathogenic fungi Beauveria bassiana and Metarhizium brunneum to soybean seeds could become endophytic and affect interactions with soybean aphid (Aphis glycines Matsumura). It was found that A. glycines population sizes increased on plants with M. brunneum (strain F52) seed inoculum, but no significant effects were shown with analogous treatments with B. bassiana (strain GHA). Fungi recovered from soybean plant tissues indicate that endophytism was established, and that B. bassiana was more prevalent. Metarhizium brunneum was only recovered from stems, but B. bassiana was recovered from stems and leaves. This work confirms that some entomopathogenic fungi can be endophytic in soybean, however, some of these fungi may have a negative effect on the plants by increasing susceptibility of soybean to A. glycines. We also used DNA sequence data to identify species of Metarhizium obtained from agricultural fields in Iowa. Phylogenetic analyses, based on DNA sequence data, found that all isolates were Metarhizium robertsii, which is consistent with past studies indicating a cosmopolitan distribution and wide host range for this species. These results are important for understanding the dynamics of implementing environmentally sustainable measures for the control of pest insects.

The harlequin ladybird, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), is native to Asia but has been intentionally introduced to many countries as a biological control agent of pest insects. In numerous countries, however, it has been introduced unintentionally. The dramatic spread of H. axyridis within many countries has been met with considerable trepidation. It is a generalist top predator, able to thrive in many habitats and across wide climatic conditions. It poses a threat to biodiversity, particularly aphidophagous insects, through competition and predation, and in many countries adverse effects have been reported on other species, particularly coccinellids. However, the patterns are not consistent around the world and seem to be affected by many factors including landscape and climate. Research on H. axyridis has provided detailed insights into invasion biology from broad patterns and processes to approaches in surveillance and monitoring. An impressive number of studies on this alien species have provided mechanistic evidence alongside models explaining large-scale patterns and processes. The involvement of citizens in monitoring this species in a number of countries around the world is inspiring and has provided data on scales that would be otherwise unachievable. Harmonia axyridis has successfully been used as a model invasive alien species and has been the inspiration for global collaborations at various scales. There is considerable scope to expand the research and associated collaborations, particularly to increase the breadth of parallel studies conducted in the native and invaded regions. Indeed a qualitative comparison of biological traits across the native and invaded range suggests that there are differences which ultimately could influence the population dynamics of this invader. Here we provide an overview of the invasion history and ecology of H. axyridis globally with consideration of future research perspectives. We reflect broadly on the contributions of such research to our understanding of invasion biology while also informing policy and people.

The soybean aphid, Aphis glycines Matsumura, is a major pest in soybean crop. Current management of this pest relies mainly on insecticides applications, and the neonicotinoid imidacloprid has been proposed as an effective insecticide to control A. glycines in soybean field. Imidacloprid at lethal concentrations not only exerts acute toxicity to A. glycines, but also cause various biological changes when aphids are chronically exposed to lower concentrations. In this study, we assessed the effects of a low-lethal (0.20 mg L-1) and two sublethal (0.05 and 0.10 mg L-1) imidacloprid concentrations on various A. glycines life history traits. Aphid exposure to 0.20 mg L-1 imidacloprid caused slower juvenile development, shorter reproductive period, and reduced adult longevity, fecundity and total lifespan. Stimulatory effects, i.e. hormesis, on reproduction and immature development duration were observed in aphids exposed to the lower sublethal imidacloprid concentrations. Consequently, the net reproduction rate (R-0) was significantly higher than in the control aphids. These findings stress the importance of the actual imidacloprid concentration in its toxicological properties on A. glycines. Therefore, our results would be useful for assessing the overall effects of imidacloprid on A. glycines and for optimizing integrated pest management programs targeting this pest.

Arthropod predators and parasitoids provide valuable ecosystem services in agricultural crops by suppressing populations of insect herbivores. Many natural enemies are influenced by non-crop habitat surrounding agricultural fields, and understanding if, and at what scales, land use patterns influence natural enemies is essential to predicting how landscape alters biological control services. Here we focus on biological control of soybean aphid, Aphis glycines Matumura, a specialist crop pest recently introduced to the north-central United States. We measured the amount of biological control service supplied to soybean in 26 replicate fields across Michigan, Wisconsin, Iowa, and Minnesota across two years (2005—2006). We measured the impact of natural enemies by experimentally excluding or allowing access to soybean aphid infested plants and comparing aphid population growth over 14 days. We also monitored aphid and natural enemy populations at large in each field. Predators, principally coccinellid beetles, dominated the natural enemy community of soybean in both years. In the absence of aphid predators, A. glycines increased significantly, with 5.3-fold higher aphid populations on plants in exclusion cages vs. the open field after 14 days. We calculated a biological control services index (BSI) based on relative suppression of aphid populations and related it to landscape diversity and composition at multiple spatial scales surrounding each site. We found that BSI values increased with landscape diversity, measured as Simpson's D. Landscapes dominated by corn and soybean fields provided less biocontrol service to soybean compared with landscapes with an abundance of crop and non-crop habitats. The abundance of Coccinellidae was related to landscape composition, with beetles being more abundant in landscapes with an abundance of forest and grassland compared with landscapes dominated by agricultural crops. Landscape diversity and composition at a scale of 1.5 km surrounding the focal field explained the greatest proportion of the variation in BSI and Coccinellidae abundance. This study indicates that natural enemies provide a regionally important ecosystem service by suppressing a key soybean pest, reducing the need for insecticide applications. Furthermore, it suggests that management to maintain or enhance landscape diversity has the potential to stabilize or increase biocontrol services.