Soybean Aphid Research Articles

Potential Overwintering Locations of Soybean Aphid (Hemiptera: Aphididae) Colonizing Soybean in Ohio and Wisconsin.

Soybean aphids, Aphis glycines Matsumura, depend on long-distance, wind-aided dispersal to complete their life cycle. Despite our general understanding of soybean aphid biology, little is explicitly known about dispersal of soybean aphids between winter and summer hosts in North America. This study compared genotypic diversity of soybean aphids sampled from several overwintering locations in the Midwest and soybean fields in Ohio and Wisconsin to test the hypothesis that these overwintering locations are sources of the soybean colonists. In addition, air parcel trajectory analyses were used to demonstrate the potential for long-distance dispersal events to occur to or from these overwintering locations. Results suggest that soybean aphids from overwintering locations along the Illinois-Iowa border and northern Indiana-Ohio are potential colonists of soybean in Ohio and Wisconsin, but that Ohio is also colonized by soybean aphids from other unknown overwintering locations. Soybean aphids in Ohio and Wisconsin exhibit a small degree of population structure that is not associated with the locations of soybean fields in which they occur, but that may be related to specific overwintering environments, multiple introductions to North America, or spatial variation in aphid phenology. There may be a limited range of suitable habitat for soybean aphid overwintering, in which case management of soybean aphids may be more effective at their overwintering sites. Further research efforts should focus on discovering more overwintering locations of soybean aphid in North America, and the relative impact of short- and long-distance dispersal events on soybean aphid population dynamics.

Temperature alters the interaction between a herbivore and a resistant host plant

Temperature and other environmental factors can strongly influence arthropods and their interactions with host plants. However, such effects are usually studied while keeping the suitability of host plants as constant as possible, thereby removing the possibility of interactions between temperature and host plant resistance. We performed experiments to determine whether temperature interacts with plant resistance to alter the density, movement, and distribution of wingless soybean aphids on resistant and susceptible soybeans. In individual plant tests, temperature influenced aphids differently depending on the plant they were on; aphids in the warmer temperature did better than aphids in the cooler temperature when on susceptible plants, but when on resistant plants aphids did worse in the warmer temperature. This pattern was, in part, due to markedly increased aphid fecundity on susceptible plants in warmer temperatures which was not the case on resistant plants. A follow-up experiment showed that higher temperature meant lower adult survival for aphids on a nutrient-poor diet, further suggesting how higher temperatures may be difficult for aphids when on resistant host plants. We also saw that both higher temperature and resistance increased within-plant movement in an additive fashion. Altering temperature and host plant resistance can each influence the demographic and movement responses of herbivores; however, this study indicates that the two factors may interact to influence herbivores in potentially unexpected ways.

Abiotic and biotic stressors causing equivalent mortality induce highly variable transcriptional responses in the soybean aphid.

Environmental stress affects basic organismal functioning and can cause physiological, developmental, and reproductive impairment. However, in many nonmodel organisms, the core molecular stress response remains poorly characterized and the extent to which stress-induced transcriptional changes differ across qualitatively different stress types is largely unexplored. The current study examines the molecular stress response of the soybean aphid (Aphis glycines) using RNA sequencing and compares transcriptional responses to multiple stressors (heat, starvation, and plant defenses) at a standardized stress level (27% adult mortality). Stress-induced transcriptional changes showed remarkable variation, with starvation, heat, and plant defensive stress altering the expression of 3985, 510, and 12 genes, respectively. Molecular responses showed little overlap across all three stressors. However, a common transcriptional stress response was identified under heat and starvation, involved with up-regulation of glycogen biosynthesis and molecular chaperones and down-regulation of bacterial endosymbiont cellular and insect cuticular components. Stressor-specific responses indicated heat affected expression of heat shock proteins and cuticular components, whereas starvation altered a diverse set of genes involved in primary metabolism, oxidative reductive processes, nucleosome and histone assembly, and the regulation of DNA repair and replication. Exposure to host plant defenses elicited the weakest response, of which half of the genes were of unknown function. This study highlights the need for standardizing stress levels when comparing across stress types and provides a basis for understanding the role of general vs. stressor specific molecular responses in aphids.

Rag Virulence Among Soybean Aphids (Hemiptera: Aphididae) in Wisconsin.

Soybean aphid, Aphis glycines Matsumura, a pest of soybean, Glycine max (L.) Merr., and native of Asia, invaded North America sometime before 2000 and rapidly became the most significant insect pest of soybean in the upper Midwest. Plant resistance, a key component of integrated pest management, has received significant attention in the past decade, and several resistance (Rag) genes have been identified. However, the efficacy of Rag (Resistance to Aphis glycines) genes in suppressing aphid abundance has been challenged by the occurrence of soybean aphids capable of overcoming Rag gene-mediated resistance. Although the occurrence of these Rag virulent biotypes poses a serious threat to effective and sustainable management of soybean aphid, little is known about the current abundance of biotypes in North America. The objective of this research was to determine the distribution of Rag virulent soybean aphids in Wisconsin. Soybean aphids were collected from Wisconsin during the summers of 2012 and 2013, and assayed for Rag1, Rag2, and Rag1+2 virulence using no-choice tests in a greenhouse. One clone from Monroe County in 2012 reacted like biotype 4, three clones in different counties in 2013 responded like biotype 2, and eight others expressed varying degrees of Rag virulence. Rag virulence in 2013 was observed in aphids from 33% of the sampled sites and was accounted for by just 4.5% of sampled clones, although this is likely a conservative estimate. No-choice test results are discussed in light of current questions on the biology, ecology, and population genetics of soybean aphid.

On-farm evaluation of a fall-seeded rye cover crop for suppression of soybean aphid (Hemiptera: Aphididae) on soybean

Cover crops offer environmental and agricultural benefits, but adoption remains low. Soybean growers have indicated that the adoption of rye as a winter cover crop would increase, if it was shown to offer suppression of a key soybean pest, the soybean aphid Aphis glycines. We performed an on-farm evaluation of two cropping systems utilized in organic production and reduced-herbicide input production. One system includes a rye cover crop, whereas the other does not. At six and five location-years in Minnesota, A. glycines and predator populations, respectively, were measured and compared between the systems with and without rye. The system with the rye cover crop significantly suppressed A. glycines populations on soybean at five of six location-years. Predators appeared to respond more to prey abundance than to plant diversity. An exposure analysis examining biological control potential revealed no differences between soybean with and without rye at any location-year. Insect control can be added to the multiple benefits of rye winter cover crops.

Synthesis and Biological Activity of Different Heterocyclic Substituted (E)-β-Farnesene Analogues

In order to discover novel aphid control agent, aphid alarm pheromone (E)-β-farnesene (EBF) was chosen as lead compound and a series of substituted EBF analogues were designed by replacing unstable conjugated double bond of EBF with different kinds of heterocyclic rings. All the compounds were synthesized and their structures were confirmed by 1 H NMR, 13 C NMR, IR spectra and HRMS analysis. Biological test showed that all the compounds displayed insecticidal or repellency ac- tivity to Myzuspersicae (Sulzer) or Aphis glycines (Matsumura). Some of them exhibited higher insecticidal activity than EBF. Introducing ester group was favorable to repellent activity. Keywords EBF analogues; heterocyclic rings; insecticidal activity; repellency activity; structure-activity relationship

Whole Genome Sequence of the Soybean Aphid Endosymbiont Buchnera aphidicola and Genetic Differentiation among Biotype-Specific Strains.

Endosymbiosis with microorganisms is common in insects, with more than 10% of species requiring the metabolic capabilities of intracellular bacteria for their nutrient acquisition. Aphids harbor an obligate mutualism with the vertically transferred endosymbiont, Buchnera aphidicola, which produces key nutrients lacking in the aphid's phloem-based diet that are necessary for normal development and reproduction. It is thought that, in some groups of insects, bacterial symbionts may play key roles in biotype evolution against host-plant resistance. The genome of Buchnera has been sequenced in several aphid strains but little genomic data is currently available for the soybean aphid (Aphis glycines), one of the most important pests of soybean in North America. In this study, DNA sequencing was used to assemble and annotate the genome sequence of the Buchnera A. glycines strain and to reconstruct phylogenetic relationships among different strains. In addition, we identified several fixed Buchnera SNPs between Aphis glycines biotypes that were avirulent or virulent to a soybean aphid resistance gene (Rag1). The results of this study describe the genetic and evolutionary relationships of the Buchnera A. glycines strain, and begin to define the roles of an aphid symbiont in host-plant resistance.

Field Abundance and Performance of Hoverflies (Diptera: Syrphidae) on Soybean Aphid

The management of the soybean aphid Aphis glycines Matsumara is a major challenge to soybean production in the north-central United States. The identification and characterization of the insect predator community has informed integrated pest management strategies by providing insight on predators that can suppress soybean aphid populations. Hoverflies (Diptera: Syrphidae) are known predators of A. glycines, but more information is needed on their diversity, abundance, and performance to evaluate their importance as biological control agents of A. glycines. In this study, syrphid abundance was evaluated across two growing seasons in four soybean fields in east-central Minnesota. Six methods were used to quantify syrphid abundance at the larval, pupal, and adult life stages; describe species composition and richness for adults; and directly compare larval abundance to aphid abundance. The syrphid community comprised eight species, dominated by Toxomerus marginatus (Say) and Toxomerus geminatus (Say). Syrphid abundance was relatively low in soybean fields. Feeding trials were conducted to compare the performance of the most common syrphid (T. marginatus) on a diet of A. glycines with two native aphids, Aphis nerii Boyer de Fonscolombe and Aphis monardae Oestlund. Despite their low abundance in soybeans, T. marginatus larvae perform well on A. glycines, A. nerii, and A. monardae in laboratory feeding trials, implying that factors other than host suitability are limiting their potential to exert biological control on soybean aphids.

Sublethal and hormesis effects of imidacloprid on the soybean aphid Aphis glycines.

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 (0.20mgL(-1)) and two sublethal (0.05 and 0.10mgL(-1)) imidacloprid concentrations on various A.glycines life history traits. Aphid exposure to 0.20mgL(-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.

Elevated expression of esterase and cytochrome P450 are related with lambda–cyhalothrin resistance and lead to cross resistance in Aphis glycines Matsumura

A resistant strain of the Aphis glycines Matsumura (CRR) has developed 76.67-fold resistance to lambda–cyhalothrin compared with the susceptible (CSS) strain. Synergists piperonyl butoxide (PBO), S,S,S-Tributyltrithiophosphate (DEF) and triphenyl phosphate (TPP) dramatically increased the toxicity of lambda–cyhalothrin to the resistant strain. Bioassay results indicated that the CRR strain had developed high levels of cross-resistance to chlorpyrifos (11.66-fold), acephate (8.20-fold), cypermethrin (53.24-fold), esfenvalerate (13.83-fold), cyfluthrin (9.64-fold), carbofuran (14.60-fold), methomyl (9.32-fold) and bifenthrin (4.81-fold), but did not have cross-resistance to chlorfenapyr, imidacloprid, diafenthiuron, abamectin. The transcriptional levels of CYP6A2-like, CYP6A14-like and cytochrome b-c1 complex subunit 9-like increased significantly in the resistant strain than that in the susceptible. Similar trend were observed in the transcripts and DNA copy number of CarE and E4 esterase. Overall, these results demonstrate that increased esterase hydrolysis activity, combined with elevated cytochrome P450 monooxygenase detoxicatication, plays an important role in the high levels of lambda–cyhalothrin resistance and can cause cross-resistance to other insecticides in the CRR strain.

Soybean aphid intrabiotype variability based on colonization of specific soybean genotypes.

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is one of the most destructive insect pests on soybeans in the United States. One method for managing this pest is through host plant resistance. Since its arrival in 2000, 4 aphid biotypes have been identified that are able to overcome soybean aphid resistance (Rag) genes. A soybean aphid isolate collected from Moline, Illinois readily colonized soybean plants with the soybean aphid resistance gene Rag2, unlike biotypes 1 and 2, but similar to soybean aphid biotype 3. Two no-choice experiments compared the virulence of the Moline isolate with biotype 3. In both experiments, differences in aphid population counts were not significant (P > 0.05) on soybean genotypes LD08-12957a (Rag2) and LD11-5413a (Rag2), but the aphid counts for the Moline isolate were significantly (P < 0.05) lower than the aphid counts for the biotype 3 isolate on the soybean genotypes Dowling (Rag1), LD05-16611 (Rag1), LD11-4576a (Rag1), and PI 567598B (rag1b and rag3). The Moline isolate was a variant of aphid biotype 3, which is the first report showing that soybean aphid isolates classified as the same biotype, based on virulence against specific Rag genes, can differ in aggressiveness or ability to colonize specific host genotypes.

A cryptic species of Aphis gossypii (Hemiptera: Aphididae) complex revealed by genetic divergence and different host plant association.

Three cryptic species, Aphis gossypii, Aphis glycines, and Aphis rhamnicola sp. nov., are recognized as sharing buckthorn plant, Rhamnus spp. as primary hosts. These aphid species have morphological similarities; however, there are significant genetic differences between the three cryptic species. Based on the high level of genetic divergence and the different secondary host association, we described a new species, Aphis rhamnicola sp. nov., for apterous and alate vivipara, fundatrix, ovipara, and gynopara, including diagnostic key for the host sharing species in the genus Aphis.

RNA-Seq reveals a xenobiotic stress response in the soybean aphid, Aphis glycines, when fed aphid-resistant soybean.

BackgroundWhile much recent research has expanded our understanding of the molecular interactions between aphids and their host plants, it is lacking for the soybean aphid, Aphis glycines. Since its North American invasion, A. glycines has become one of the most damaging insect pests on this important crop. Five soybean genes for host plant resistance to A. glycines have been identified, but populations of A. glycines have already adapted to overcome these resistance genes. Understanding the molecular interactions between resistant soybean and A. glycines can provide clues to its adaptation mechanisms. Here, we used RNA-Sequencing to compare and contrast A. glycines gene expression when fed resistant (Rag1) and susceptible soybean.ResultsCombining results from a previous A. glycines transcriptome, we generated 64,860 high quality transcripts, totaling 41,151,086 bases. Statistical analysis revealed 914 genes with significant differential expression. Most genes with higher expression in A. glycines on resistant plants (N = 352) were related to stress and detoxification such as cytochrome P450s, glutathione-S-transferases, carboxyesterases, and ABC transporters. A total of 562 genes showed lower transcript abundance in A. glycines on resistant plants. From our extensive transcriptome data, we also identified genes encoding for putative salivary effector proteins (N = 73). Among these, 6 effector genes have lower transcript abundance in A. glycines feeding on resistant soybean.ConclusionsOverall, A. glycines exhibited a pattern typical of xenobiotic challenge, thereby validating antibiosis in Rag1, presumably mediated through toxic secondary metabolites. Additionally, this study identified many A. glycines genes and gene families at the forefront of its molecular interaction with soybean. Further investigation of these genes in other biotypes may reveal adaptation mechanisms to resistant plants.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-972) contains supplementary material, which is available to authorized users.

Diel variation in the abundance and composition of the predator assemblages feeding on aphid-infested soybean

Many predatory arthropods are nocturnal, yet the potential contribution of nocturnal predators to biological control is often overlooked. The soybean aphid, Aphis glycines Matsumura, has emerged as a significant pest of soybean in the North Central US. Soybean aphid biological control research has focused on diurnal predators. Here, we used video cameras to continuously monitor soybean plants infested with soybean aphids, compare the diurnal and nocturnal predator communities on those plants, and assess predator activity during different times of day. Different predator communities were observed being active on soybean during day and night. Coccinellids and anthocorids dominated the diurnal predator community, while Opiliones and Araneae dominated the nocturnal predator community. Nocturnal and diurnal predators were recorded being active for similar rates per hour. Future research is needed to clarify the significance of arachnid predators and other nocturnal generalists to soybean aphid biocontrol.

Stability of Soybean Aphid Resistance in Soybean Across Different Temperatures

ABSTRACTThe soybean aphid (Aphis glycines Matsumura) is the most important insect pest posing a threat to soybean [Glycine max (L.) Merr.] grain production in the United States. Soybean cultivars with resistance are currently being deployed to aid in management of the pest. Temperature has been reported to influence the expression of host plant resistance against crop pests. The objective of this study was to determine if temperatures, 14, 21, and 28°C, altered resistance expression in four aphid‐resistant soybean genotypes, LD05‐16611 (with the Rag1 resistance gene), PI 200538 (Rag2), PI 567541B (rag1c, rag4), and PI 567597C (antixenosis) compared to a susceptible soybean genotype (Williams 82) when challenged with soybean aphid. A replicated no‐choice experiment was conducted and aphid populations of the three soybean aphid biotypes, 1, 2, and 3, were enumerated 14 d after inoculating the five soybean genotypes. Significant interactions were found in the analysis of the effects of temperature, soybean genotype, and aphid biotype on aphid populations. Responses between soybean genotypes and aphid biotypes were consistent with previous reports with the exception of PI 567541B, which had lower resistance against aphid biotype 1 than found in an earlier study. At 14°C, there was limited aphid population growth on all soybean genotypes, including Williams 82. At 21 and 28°C, resistance expression was stable in LD05‐16611 (Rag1), PI 567541B (rag1c, rag4), and PI 567597C (antixenosis), relative to susceptible Williams 82; however, resistance expressed in PI 200538 (Rag2) was significantly stronger at 28°C than at 21°C, as indicated by differences in aphid population size that were found. Results of this study indicated that soybean aphid virulence variability had a stronger influence on the effectiveness of soybean aphid resistance than did temperature, and that the aphid resistance tested in this study would remain stable or be stronger in temperatures ranging between 21 and 28°C.

Identification of Resistance to Soybean Aphids in Early Germplasm

ABSTRACTThe soybean aphid (Aphis glycines Matsumura) causes agricultural losses worldwide. Identifying sources of soybean resistance to the soybean aphid is a key strategy in preventing crop damage caused by this pest. Three hundred accessions of cultivated soybean [Glycine max (L.) Merr.] and two hundred accessions of wild soybean (G. soja) originally from northeastern China were evaluated in 2011 and 2012. The objectives of this study were to identify sources and types of resistance to the soybean aphid in early‐maturing soybean germplasm. First, two preliminary choice tests were performed. Accessions that had been identified as aphid resistant in the two choice tests were simultaneously re‐evaluated in a pot choice test, pot no‐choice test, and field no‐choice test to determine the type of resistance. The results of all tests showed that 4 of the 500 accessions were resistant to the soybean aphid. The results of a confirmation test indicated that the logarithmic value and the damage index 25 d after inoculation of accessions ZDD0326, ZDD0219, ZYD00022, and ZYD00033 were significantly (P &lt; 0.05) different from those of susceptible checks in the pot choice test. Accessions ZDD0219, ZYD00022, and ZYD00033 had significantly lower logarithmic values and significantly lower damage index (DI) values than the susceptible checks in the pot and field no‐choice tests (P &lt; 0.05). Evidence indicated that ZDD0219, ZYD00022, and ZYD00033 have antibiotic resistance, and ZDD0326 has antixenosis resistance.

Impact of nitrogen fixing and plant growth-promoting bacteria on a phloem-feeding soybean herbivore

In soybean (Glycine max L.) production systems, growers often inoculate seeds with the symbiotic N-fixing species Bradyrhizobium japonicum along with other bacterial species or chemicals intended to enhance plant growth and yield. However, microbes associated with plant roots can also impact the biology of above-ground insect herbivores through influencing various aspects of plant physiology, with effects dependent on the bacterial species. Because rhizobial seed inoculants can potentially affect densities of soybean herbivores, we investigated the performance of phloem-feeding soybean aphids (Aphis glycines Matsumura) on: (1) soybeans receiving one of four commercially available rhizobial seed inoculants, (2) non-inoculated soybeans associated with existing soil bacteria, or (3) non-inoculated soybeans receiving high levels of fertilizer to suppress N-fixation while still providing adequate N as nitrate. We quantified effects of inoculants and aphid presence on parameters associated with plant growth, N-fixation, and foliar N levels, and explored relationships between aphid densities and these plant parameters. Regardless of inoculation treatment, aphid presence negatively affected plant biomass, pod density, and total N concentration in aerial plant tissues, although, effects on the concentration of ureide N (primary products of N-fixation) were not significant. Inoculant identity significantly impacted aphid populations in both short- (1 week) and longer-term experiments (2 months), with pest densities negatively related to the number of root nodules per plant. This research indicates that nodulation status of soybeans can influence above-ground herbivores.

Grassland plantings and landscape natural areas both influence insect natural enemies

Local habitat management and landscape composition are main factors in determining the abundance and diversity of conservation biological control agents. In Midwestern U.S.A., the establishment of conservation plantings is encouraged through government programs. These plantings buffer streams from agricultural inputs and increase wildlife habitat. We examined the effects that these plantings and semi-natural areas in the surrounding landscape have upon the abundance and diversity of natural enemies of the soybean aphid. We quantified abundances of soybean aphids and their natural enemies in soybean fields and adjacent plantings in Newton County, Indiana, U.S.A. We found a higher number of natural enemies in conservation plantings than in soybean fields before aphids arrived. When soybean aphid populations were increasing, aphid abundance was a main factor influencing the four major predator groups (Anthocoridae, Nabidae, and exotic and native Coccinellidae). Along with aphid abundance, the presence of adjacent plantings and forest areas within 3km affected nabid abundance and the presence of adjacent plantings and grassy areas within 5km influenced the abundance of native coccinellid in soybean fields. Lastly, this study showed that the presence of grassland strips enhances beta diversity of natural enemies in soybean fields. Therefore, natural enemy communities may be more resilient to disturbance in landscapes containing conservation plantings. The increased natural enemy abundance with plantings and semi-natural areas in the surrounding landscape may enhance conservation biological control and benefit farmers.

The impact of prairie strips on aphidophagous predator abundance and soybean aphid predation in agricultural catchments.

Reconstructing prairie vegetation in row crop-dominated agricultural landscapes may contribute to several ecosystem services, including the biological control of insect pests, such as the soybean aphid Aphis glycines Matsumura. The influence of the amount and configuration of reconstructed prairie vegetation on the delivery of ecosystem services was investigated in several small catchments at Neal Smith National Wildlife Refuge in Iowa. Treatments include catchments entirely in row crops under a no-till, corn-soybean (Zea mays L.-Glycine max [L.] Merrill) rotation, catchments with 10% of the land in prairie located at the base, and catchments with 10 or 20% of the land in multiple contour strips of prairie. During 2009 and 2011 growing seasons, we measured abundance and diversity of aphidophagous insect predators in response to treatment and habitat type (i.e., soybean, prairie). In 2011, we further studied the biological control of soybean aphids by artificially infesting uncaged and caged plants to prevent exposure from predators. While aphidophagous predators were more abundant in prairie, populations of key aphid predators did not significantly differ among treatments. Biological control of the soybean aphid did not differ among treatments or with distance from prairie. Our results suggest that prairie strips, in addition to providing soil and water quality benefits, may increase the populations of beneficial insects, but may not directly impact biocontrol. We propose several hypotheses to explain why we did not observe more soybean aphid predation with the increased abundance of aphidophagous predators in catchments containing prairie.

Characterization of Peroxidase Changes in Tolerant and Susceptible Soybeans Challenged by Soybean Aphid (Hemiptera: Aphididae).

Changes in protein content, peroxidase activity, and isozyme profiles in response to soybean aphid feeding were documented at V1 (fully developed leaves at unifoliate node, first trifoliate leaf unrolled) and V3 (fully developed leaf at second trifoliate node, third trifoliate leaf unrolled) stages of soybean aphid-tolerant (KS4202) and -susceptible (SD76R) soybeans. Protein content was similar between infested and control V1 and V3 stage plants for both KS4202 and SD76R at 6, 16, and 22 d after aphid introduction. Enzyme kinetics studies documented that control and aphid-infested KS4202 V1 stage and SD76R V1 and V3 stages had similar levels of peroxidase activity at the three time points evaluated. In contrast, KS4202 aphid-infested plants at the V3 stage had significantly higher peroxidase activity levels than control plants at 6 and 22 d after aphid introduction. The differences in peroxidase activity observed between infested and control V3 stage KS4202 plants at these two time points suggest that peroxidases may be playing multiple roles in the tolerant plant. Native gels stained for peroxidase were able to detect differences in the isozyme profiles of aphid-infested and control plants for both KS4202 and SD76R.