Genetic mapping shows intraspecific variation and transgressive segregation for caterpillar‐induced aphid resistance in maize

Plants in nature have inducible defences that sometimes lead to targeted resistance against particular herbivores, but susceptibility to others. The metabolic diversity and genetic resources available for maize (Zea mays) make this a suitable system for a mechanistic study of within‐species variation in such plant‐mediated interactions between herbivores. Beet armyworms (Spodoptera exigua) and corn leaf aphids (Rhopalosiphum maidis) are two naturally occurring maize herbivores with different feeding habits. Whereas chewing herbivore‐induced methylation of 2,4‐dihydroxy‐7‐methoxy‐1,4‐benzoxazin‐3‐one glucoside (DIMBOA‐Glc) to form 2‐hydroxy‐4,7‐dimethoxy‐1,4‐benzoxazin‐3‐one glucoside (HDMBOA‐Glc) promotes caterpillar resistance, lower DIMBOA‐Glc levels favour aphid reproduction. Thus, caterpillar‐induced DIMBOA‐Glc methyltransferase activity in maize is predicted to promote aphid growth. To test this hypothesis, the impact of S. exigua feeding on R. maidis progeny production was assessed using seventeen genetically diverse maize inbred lines. Whereas aphid progeny production was increased by prior caterpillar feeding on lines B73, Ki11, Ki3 and Tx303, it decreased on lines Ky21, CML103, Mo18W and W22. Genetic mapping of this trait in a population of B73 × Ky21 recombinant inbred lines identified significant quantitative trait loci on maize chromosomes 1, 7 and 10. There is a transgressive segregation for aphid resistance, with the Ky21 alleles on chromosomes 1 and 7 and the B73 allele on chromosome 10 increasing aphid progeny production. The chromosome 1 QTL coincides with a cluster of three maize genes encoding benzoxazinoid O‐methyltransferases that convert DIMBOA‐Glc to HDMBOA‐Glc. Gene expression studies and benzoxazinoid measurements indicate that S. exigua ‐induced responses in this pathway differentially affect R. maidis resistance in B73 and Ky21.     

Community‐wide impact of an exotic aphid on introduced tall goldenrod

1. The aphid Uroleucon nigrotuberculatum Olive, which is specialised to the tall goldenrod, Solidago altissima L., in its native range, has become a dominant species on the introduced tall goldenrod in Japan. How this exotic aphid influenced arthropod communities on the introduced tall goldenrod in aphid‐present (spring) and aphid‐absent (autumn) seasons was examined, using an aphid removal experiment. 2. In spring, aphid presence increased ant abundance because aphid honeydew attracted foraging ant workers. A significant negative correlation was found between the numbers of ants and herbivorous insects other than aphids on the aphid‐exposed plants, but no significant correlation was detected on the aphid‐free plants. Thus, the aphid presence was likely to decrease the abundance of co‐occurring herbivorous insects through removal behaviour of the aphid‐tending ants. There were no significant differences in plant traits between the aphid‐exposed and aphid‐free plants. 3. In autumn, the numbers of lateral shoots and leaves, and the leaf nitrogen content were increased in response to the aphid infestation in spring. Because of the improvement of plant traits by aphid feeding, the abundance of leaf chewers increased on aphid‐exposed plants. In contrast, the abundance of sap feeders decreased on the aphid‐exposed plants. In particular, the dominant scale insect among sap feeders, Parasaissetia nigra Nietner, decreased, followed by a decrease in the abundance of ants attending P. nigra. Thus, aphid feeding may have attenuated the negative impacts of the tending ants on leaf chewers. 4. Aphid presence did not change herbivore species richness but changed the relative density of dominant herbivores, resulting in community‐wide effects on co‐occurring herbivores through ant‐mediated indirect effects, and on temporally separated herbivores through plant‐ and ant‐mediated indirect effects. The aphid also altered predator community composition by increasing and decreasing the relative abundance of aphid‐tending ants in the spring and autumn, respectively.     

The value of three cereal aphid species as food for a generalist predator

The value of the cereal aphid species Metopolophium dirhodum (Wlk.), Sitobion avenae (F.) and Rhopalosiphum padi (L.) as prey for the linyphiid spider Erigone atra (Bl.) was assessed. Fecundity of females was determined for spiders fed on eight experimental diets: three single‐species aphid diets, a mixed diet of all three aphid species, three mixed diets with each aphid species in combination with fruit flies Drosophila melanogaster (Meig.), and pure D. melanogaster as a high quality comparison diet. The development and survival of first‐instar juveniles fed on three diets of single aphid species, and on a diet of Collembola were compared with those subjected to starvation. Prey value for adult females was assessed by egg production, hatching success and offspring size. In pure diets all three aphid species were of low value to the spiders, causing a rapid decline in egg production and supporting no growth of significance of first‐instar juveniles. No difference in value of aphid species of single‐species aphid diets was found in the fecundity experiment, while a ranking of aphid species of M. dirhodum > R. padi > S. avenae was revealed in the survivorship experiment. A mixed‐aphid diet was not found to be advantageous compared with single‐species aphid diets, and no advantage of including aphids in mixed diets with fruit flies was found. Metopolophium dirhodum and R. padi were neutral in mixed diets, while a diet of S. avenae and fruit flies caused reduced egg production compared with the pure diet of fruit flies, revealing a toxic effect of S. avenae on the spider. The value‐ranking of aphid species in mixed diets was similar to that of single‐species diets. A similar ranking of aphid species was found for different fitness parameters (fecundity of adult females and development of juveniles). A ranking of aphids by offspring size of mothers on aphid‐only diets was S. avenae > M. dirhodum > R. padi. All aphid‐fruit fly diets resulted in larger offspring than a diet of only D. melanogaster, with the overall largest offspring being produced on the diet of M. dirhodum and fruit flies.     

The genetic structure of Aphis gossypii populations in Japanese fruit orchards

The genetic structure of Aphis gossypii Glover (Hemiptera: Aphididae) populations was characterized using microsatellite analysis of insects sampled from pear and citrus orchards at three locations in the summer seasons of 2001 and 2003. These data will enable more precise forecasting of infestation and will be of value to the development of better control methods. In total, 89 genotypes were found in 500 aphid samples. The diversity indices in aphid populations on pear trees fluctuated but showed a decrease with time in citrus orchards. Japanese aphid populations have greater variation in their microsatellite loci than African, European, or Southeast Asian populations. Approximately half of the genotypes were found in only one colony, whereas the remainder were identified in two or more colonies. Fifteen genotypes appeared in different years, in samples from different areas, or on different host plants. Our data suggest the existence of aphid populations with pear‐adapted genotypes and with a permanent parthenogenetic life cycle. Some of the genotypes included genes conferring resistance to pirimicarb and pyrethroid insecticides. Japanese A. gossypii populations may maintain their large genetic variation through differences in their life cycles.     

Effects of Rag1 aphid‐resistant soybean on mortality,development, and preference of brown marmorated stink bug

The brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), poses a new threat to soybean, Glycine max (L.) Merrill (Fabaceae), production in the north central USA. As H. halys continues to spread and increase in abundance in the region, the interaction between H. halys and management tactics deployed for other pests must be determined. Currently, the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is the most abundant and damaging insect pest of soybean in the region. Aphid‐resistant soybean, mainly with the Rag1 gene, is commercially available for management of A. glycines. Here, experiments were performed to evaluate the effects of Rag1 aphid‐resistant soybean on the mortality, development, and preference of H. halys. In a no‐choice test, mortality of H. halys reared on Rag1 aphid‐resistant soybean pods was significantly lower than when reared on aphid‐susceptible soybean pods (28 vs. 53%). Development time, adult weight, and proportion females of surviving adults did not differ when reared on Rag1 aphid‐resistant or aphid‐susceptible soybean pods. In choice tests, H. halys exhibited a preference for Rag1 aphid‐resistant over aphid‐susceptible soybean pods after 4 h, but not after 24 h. Halyomorpha halys exhibited no preference when tested with vegetative‐stage or reproductive‐stage soybean plants. The preference by H. halys for Rag1 aphid‐resistant soybean pods and the decreased mortality when reared on these pods suggests that the use of Rag1 aphid‐resistant soybean may favor this emerging pest in the north central USA.     

Possible roles of esterase, glutathione S-transferase, and superoxide dismutase activities in understanding aphid–cereal interactions

Activities of the detoxification enzymes esterase, glutathione S‐transferase, and of superoxide dismutase in aphids and aphid‐infested cereal leaves were assayed using polyacrylamide gel electrophoresis and a spectrophotometer to elucidate the enzymatic mechanisms of aphid resistance in cereal plants. A chlorosis‐eliciting Russian wheat aphid, Diuraphis noxia (Mordvilko), and non‐chlorosis‐eliciting bird cherry‐oat aphid, Rhopalosiphum padi (L.), and four cereals were used in this study. The four cereal genotypes were ‘Arapahoe’ (susceptible) and ‘Halt’ (resistant) wheat (Triticum aestivum L.), ‘Morex’ (susceptible) barley (Hordeum vulgare L.), and ‘Border’ (resistant) oat (Avena sativa L.). Esterase isozymes differed between the two aphid species, although glutathione S‐transferase and superoxide dismutase did not. Esterase, glutathione S‐transferase, and superoxide dismutase activities in either aphid species were not affected by the level of resistance of a cereal to D. noxia. The assays of cereal leaf samples showed that D. noxia feeding elicited an increase in esterase activity in all four cereal genotypes, although R. padi feeding did not. The increase of esterase activity in cereals, however, was not correlated to aphid resistance in the cereals. The time‐series assays of aphid‐infested cereal leaves showed that D. noxia‐infested Morex barley had a significant increase in esterase activity on all sampling dates (3, 6, and 9 days) in comparison with either uninfested or R. padi‐infested barley. No difference in glutathione S‐transferase activity was detected among either aphid infestations or sampling dates. The electrophoretic assays, however, revealed that aphid feeding elicited a significant increase in superoxide dismutase activity, which served as the control of glutathione S‐transferase activity assays. The increase in esterase and superoxide dismutase activities suggested that D. noxia feeding imposes not only toxic, but also oxidative stresses on the cereals. The ramification of using these enzyme activity data to understand the etiology of D. noxia‐elicited chlorosis is discussed.     

Introduced ants reduce interaction diversity in a multi‐species,ant–aphid mutualism

Mutualisms contribute in fundamental ways to the origin, maintenance and organization of biological diversity. Introduced species commonly participate in mutualisms, but how this phenomenon affects patterns of interactions among native mutualists remains incompletely understood. Here we examine how networks of interactions among aphid‐tending ants, ant‐tended aphids, and aphid‐attacking parasitoid wasps differ between 12 spatially paired riparian study sites with and without the introduced Argentine ant Linepithema humile in southern California. To resolve challenges in species identification, we used DNA barcoding to identify aphids and screen for parasitoid wasps (developing inside their aphid hosts) from 170 aphid aggregations sampled on arroyo willow Salix lasiolepis. Compared to uninvaded sites, invaded sites supported significantly fewer species of aphid‐tending ants and ant‐tended aphids. At invaded sites, for example, we found only two species of ant‐tended aphids, which were exclusively tended by L. humile, whereas at uninvaded sites we found 20 unique ant–aphid interactions involving eight species of ant‐tended aphids and nine species of aphid‐tending ants. Ant–aphid linkage density was thus significantly lower at invaded sites compared to uninvaded sites. We detected aphid parasitoids in 14% (28/198) of all aphid aggregations. Although the level of parasitism did not differ between invaded and uninvaded sites, more species of wasps were detected within uninvaded sites compared to invaded sites. These results provide a striking example of how the assimilation of introduced species into multi‐species mutualisms can reduce interaction diversity with potential consequences for species persistence.     

Abscisic acid deficiency increases defence responses against Myzus persicae in Arabidopsis

Comparison of Arabidopsis thaliana (Arabidopsis) gene expression induced by Myzus persicae (green peach aphid) feeding, aphid saliva infiltration and abscisic acid (ABA) treatment showed a significant positive correlation. In particular, ABA‐regulated genes are over‐represented among genes that are induced by M. persicae saliva infiltration into Arabidopsis leaves. This suggests that the induction of ABA‐related gene expression could be an important component of the Arabidopsis–aphid interaction. Consistent with this hypothesis, M. persicae populations induced ABA production in wild‐type plants. Furthermore, aphid populations were smaller on Arabidopsis aba1‐1 mutants, which cannot synthesize ABA, and showed a significant preference for wild‐type plants compared with the mutant. Total free amino acids, which play an important role in aphid nutrition, were not altered in the aba1‐1 mutant line, but the levels of isoleucine (Ile) and tryptophan (Trp) were differentially affected by aphids in wild‐type and mutant plants. Recently, indole glucosinolates have been shown to promote aphid resistance in Arabidopsis. In this study, 4‐methoxyindol‐3‐ylmethylglucosinolate was more abundant in the aba1‐1 mutant than in wild‐type Arabidopsis, suggesting that the induction of ABA signals that decrease the accumulation of defence compounds may be beneficial for aphids.     

Microsatellite isolation and characterization in the beneficial parasitoid wasp Diaeretiella rapae (M’Intosh) (Hymenoptera: Braconidae: Aphidiinae)

The primary parasitoid wasp, Diaeretiella rapae (M’Intosh), is used as a biological control agent in insect pest management strategies to combat aphid pests, mainly on cruciferous plants. To investigate the spatial scales over which this beneficial parasitoid wasp moves within an agricultural landscape, we developed five polymorphic microsatellite markers. The number of alleles per locus ranged from 11 to 21. Cross‐species amplification indicated that these loci may be useful in some other members of the Aphidiinae.     

Elevated temperatures alter an ant‐aphid mutualism

Ant‐hemipteran mutualisms are keystone interactions that can be variously affected by warming: these mutualisms can be strengthened or weakened, or the species can transition to new mutualist partners. We examined the effects of elevated temperatures on an ant‐aphid mutualism in the subalpine zone of the Rocky Mountains in Colorado, USA. In this system, inflorescences of the host plant, Ligusticum porteri Coult. & Rose (Apiaceae), are colonized by the ant‐tended aphid Aphis asclepiadis Fitch or less frequently by the non‐ant tended aphid Cavariella aegopodii (Scopoli) (both Hemiptera: Aphididae). Using an 8‐year observational study, we tested for two key mechanisms by which ant‐hemipteran mutualisms may be altered by climate change: shifts in species identity and phenological mismatch. Whereas the aphid species colonizing the host plant is not changing in response to year‐to‐year variation in temperature, we found evidence that a phenological mismatch between ants and aphids could occur. In warmer years, colonization of host plant inflorescences by ants is decreased, whereas for A. asclepiadis aphids, host plant colonization is mostly responsive to date of snowmelt. We also experimentally established A. asclepiadis colonies on replicate host plants at ambient and elevated temperatures. Ant abundance did not differ between aphid colonies at ambient vs. elevated temperatures, but ants were less likely to engage in tending behaviors on aphid colonies at elevated temperatures. Sugar composition of aphid honeydew was also altered by experimental warming. Despite reduced tending by ants, aphid colonies at elevated temperatures had fewer intraguild predators. Altogether, our results suggest that higher temperatures may disrupt this ant‐aphid mutualism through both phenological mismatch and by altering benefits exchanged in the interaction.     

Clonal composition of the peach-potato aphid Myzus persicae (Homoptera: Aphididae) in France and Scotland: Comparative analysis with IGS fingerprinting and microsatellite markers

Fourteen colonies of the peach‐potato aphid, Myzus persicae, were taken either from French peach trees or weeds in 2001. Thirty five apomictic parthenogenetic lineages (APLs) were established. Ribosomal DNA intergenic spacer (IGS) fingerprinting was used to characterise these and 28 fingerprints were duly obtained. Those lineages with different fingerprints were considered different genotypes and those with the same fingerprint as the same. The genetic identity of APLs was further tested using four microsatellite loci. APLs that differed by IGS fingerprint had distinct microsatellite allele combinations and those that had the same IGS fingerprint had the same microsatellite allele combinations. The results confirmed that IGS types corresponded to different aphid genotypes. Independent APLs with identical IGS and microsatellite genotype were therefore considered different representatives of the same clone. APLs from M. persicae found on Scottish crops in 1995, 1996 and 2001, as well as a long‐term laboratory line were also examined by the same methods. Their IGS fingerprints were similar or identical suggesting that they all belonged to the same clone. Microsatellite markers also suggested that these lineages were derived from a single clone. Some field lineages exhibited slight modifications to their IGS fingerprints confirming that the IGS evolves more rapidly than these microsatellite alleles. Thus, IGS will continue to provide a useful marker for aphid fieldwork.     

Habitat variation,mutualism and predation shape the spatio‐temporal dynamics of tansy aphids

1. Spatially distributed resources can lead to the formation of metapopulations, where individual subpopulations are often small and can experience frequent local extinction events followed by recolonisation. An example of terrestrial metapopulations are specialised phytophagous insects on their patchily distributed host plants. 2. The present study investigated the population dynamics of a specialised aphid (Metopeurum fuscoviride) on its patchily distributed host plant (Tanacetum vulgare) and associated community of mutualistic ants and predators in a small‐scale field site. Furthermore, aphid habitat differences (plant size, C/N ratio, location and surrounding vegetation) were quantified, and seasonal timing and precipitation were considered. 3. Seasonal timing and precipitation both had effects on aphid colonisation, extinction events and aphid colony persistence. Towards the end of the season, and after higher precipitation, aphid colonisation events decreased and extinction events increased. Plant size and location as well as aphid within‐field dispersal determined the spatio‐temporal distribution of aphid colonies. 4. Mutualistic ants (Lasius niger and Myrmica rubra) increased the chance of establishment of aphid colonies. However, when M. rubra was tending, aphid colony persistence was reduced. Aphid persistence and extinction were dependent on aphid abundance, as a higher colony size reduced the probability of extinction by predation. 5. The results emphasise the importance of dispersal limitation, population growth and the presence of mutualists when studying the spatio‐temporal dynamics of tansy aphids, particularly in a small‐scale field site.     

Collembola respond to aphid herbivory but not to honeydew addition

Abstract. 1. Euedaphic collembola alter their soil distribution in response to above‐ground aphid herbivory of Poa annua L. Graminae, a host grass. 2. Two mechanisms potentially underpin this effect. Carbon‐rich aphid honeydew falling onto the soil surface may affect mycophagous collembola; alternatively aphid‐induced changes in root biomass may be necessary to produce changes in collembola abundance. 3. When compared to a plant‐only control, aphid herbivory increased the number of collembola in the top 5 cm of soil, reduced both foliar and root biomass, and increased shoot/root ratio. Honeydew addition had no effect on collembola numbers or any recorded host‐plant parameter. 4. Honeydew deposition is not responsible for the increased numbers of collembola found in the upper soil after aphid herbivory; aphid‐induced reductions in root biomass may be the most important factor explaining knock‐on effects of aphid herbivory on soil fauna.     

Evaluation of induced responses, insect population growth, and host-plant fitness may change the outcome of tests of the preference-performance hypothesis: a case study

The preference‐performance hypothesis predicts that insect preference should correspond to host suitability for offspring development. We studied the pattern of within‐plant preference in the aphid Sipha flava and its consequences for offspring performance on the host‐plant Sorghum halepense, regarding the role of induced responses of plants to aphid feeding. The consequences of within‐plant preference on aphid population growth and host‐plant traits were also evaluated. Our results showed that winged and wingless aphids preferred to settle on mature rather than young leaves. In contrast, aphid individual growth rate was higher on young leaves when compared with mature leaves, suggesting that the outcome of this test rejected the preference‐performance hypothesis. However, the inclusion of the factor ‘previous aphid infestation’ changed the outcome from a maladaptive choice to a neutral one. Thus, individual growth rates of S. flava increased when aphids developed on leaves that had been previously infested. Interestingly, aphid growth rate on previously infested leaves did not differ between young and mature leaves. On the other hand, aphid population reproductive rate was higher and the percentage of winged aphids lower when infestation occurred on mature rather than young leaves. Aphid infestation reduced plant and shoot biomass, and increased leaf mortality. These negative effects on plant traits related to plant fitness were greater when aphid infestation occurred on young leaves. Likewise, whereas infestation on mature leaves did not cause a significant reduction in the number of flowering plants compared with control plants, aphid infestation on young leaves did reduce the number of plants at the flowering stage. Consequently, if both the reproductive rate of aphids in the mid‐term, and host‐plant fitness are taken into account, the results indicate that aphid preference for mature leaves may be an adaptive choice, thus supporting the preference‐performance hypothesis.     

Aphids decelerate litter nitrogen mineralisation through changes in litter quality

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Responses of summer cereal aphid populations to reduced rate aphicide applications in field plots of winter wheat

Abstract 1 Recommended and reduced rate applications of pirimicarb and alpha‐cypermethrin were applied to winter wheat crops to control summer infestations of grain aphid (Sitobion avenae) and rose‐grain aphid (Metopolophium dirhodum). 2 Aphid numbers were assessed weekly and the yield response to treatment application was compared with accumulated aphid days on the crop. 3 Responses to aphicide treatment varied between sites according to variations in the subsequent development of aphid populations under varying weather conditions and differential pressures from aphid natural enemies. 4 Alpha‐cypermethrin treatment reduced spider density at most sites, and also resulted in a resurgence of aphid populations at three sites.     

The effect of fractionated Tagetes oil volatiles on aphid reproduction

The biological activity of essential oil volatiles from Tagetes minuta L. (Mexican marigold) against three aphid species was investigated in a series of laboratory experiments. The aphid species (Homoptera: Aphididae) studied were: Acyrthosiphon pisum (Harris) (pea aphid), Myzus persicae (Sulzer) (peach‐potato aphid), and Aulacorthum solani (Kaltenbach) (glasshouse and potato aphid). Tagetes minuta oil volatiles significantly reduced aphid reproduction (up to 100% after 5 days of exposure). The effect depended on the quantity of essential oil used, and varied with the aphid species tested. Pea aphids were the most susceptible. Tagetes minuta oil was fractionated by vacuum distillation. Fractions and three pure compounds (limonene, (Z)‐ocimene, and β‐caryophyllene) were tested using the same experimental technique. The chemical composition of the volatiles was investigated by headspace–solid phase microextraction–gas chromatography mass spectrometry (HS‐SPME‐GCMS), and the main constituents of the oil were identified. Overall, applied in equal quantity, fractions predominantly containing sesquiterpenes and oxygenated monoterpenoids were more effective in restricting aphid population growth than fractions predominantly containing monoterpenes. When tested as a pure compound, the sesquiterpene β‐caryophyllene produced a greater effect than the monoterpenes limonene and ocimene. The study demonstrates that T. minuta oil volatiles have potential for aphid control.     

Role of terpenes from aphid-infested potato on searching and oviposition behavior of Episyrphus balteatus

To cope with pathogen and insect attacks, plants develop different mechanisms of defence, in both direct （physical and chemical） and indirect ways （attractive volatiles to entomophagous beneficials）. Plants are then able to express traits that facilitate ＂top-down＂ control of pests by attracting herbivore predators. Here we investigate the indirect defence mechanism of potato plants by analyzing the volatile patterns of both healthy and aphid- infested plants. Important changes in the emitted terpene pattern by the Myzus persicae infested host plant were observed. Using Solid Phase MicroExtraction （SPME） and GC-MS, the （E）-fl-farnesene （EBF） appeared to be emitted by aphid-infested potato and not by healthy plants. To assess the infochemical role of these volatile releases after aphid damage on the aphidophagous predators Episyrphus balteams, the hoverfly foraging behavior was assessed using the Observer 5.0 software （Noldus, Wageningen, The Netherlands）. Aphidfree potato plants were also used as a control volatile source in the predator behavioral study. While aphid-infested plants induced efficient searching and acceptation behaviors leading to egg-laying, no kairomonal effect of healthy potato plants was observed, leading to longer immobility durations and shorter searching periods in the net cage. High oviposition rate of E. balteatus was observed when aphid-infested potato was used （mean of 48.9 eggs per laying and per female）. On the other hand, no egg was produced by the hoverfly on healthy aphid-free plants. The E. balteatus foraging and reproductive behaviors according to the volatile emission from aphid-infested plants are discussed in relation to the potential use of active infochemical molecules in integrated aphid pest management.     

Performance and prospects of Rag genes for management of soybean aphid

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is an invasive insect pest of soybean [Glycine max (L.) Merr. (Fabaceae)] in North America, and it has led to extensive insecticide use in northern soybean‐growing regions there. Host plant resistance is one potential alternative strategy for managing soybean aphid. Several Rag genes that show antibiosis and antixenosis to soybean aphid have been recently identified in soybean, and field‐testing and commercial release of resistant soybean lines have followed. In this article, we review results of field tests with soybean lines containing Rag genes in North America, then present results from a coordinated regional test across several field sites in the north‐central USA, and finally discuss prospects for use of Rag genes to manage soybean aphids. Field tests conducted independently at multiple sites showed that soybean aphid populations peaked in late summer on lines with Rag1 or Rag2 and reached economically injurious levels on susceptible lines, whereas lines with a pyramid of Rag1 + Rag2 held soybean aphid populations below economic levels. In the regional test, aphid populations were generally suppressed by lines containing one of the Rag genes. Aphids reached putative economic levels on Rag1 lines for some site years, but yield loss was moderated, indicating that Rag1 may confer tolerance to soybean aphid in addition to antibiosis and antixenosis. Moreover, no yield penalty has been found for lines with Rag1, Rag2, or pyramids. Results suggest that use of aphid‐resistant soybean lines with Rag genes may be viable for managing soybean aphids. However, virulent biotypes of soybean aphid were identified before release of aphid‐resistant soybean, and thus a strategy for optimal deployment of aphid‐resistant soybean is needed to ensure sustainability of this technology.     

Cross‐species amplification of microsatellite loci in aphids: assessment and application

Despite the relative ease of isolating microsatellites, their development still requires substantial inputs of time, money and expertise. For this reason there is considerable interest in using existing microsatellites on species from which markers were not cloned. We tested cross‐species amplification of 48 existing aphid loci in species of the following genera: Aphidinae: Aphidini: Aphis and Rhopalosiphum; Aphidinae: Macrosiphini: Acyrthosiphum, Brevicoryne, Diuraphis, Illinoia, Macrosiphoniella, Macrosiphum, Metopeurum, Metapolophium, Myzus, Phorodon, Sitobion and Uroleucon and Neuquenaphidinae: Neuquenaphis. Our results show cross‐species application of known microsatellite loci is a highly promising source of codominant markers for population genetic and evolutionary studies in aphids.