Parasitism of the soybean aphid, Aphis glycines by Binodoxys communis: the role of aphid defensive behaviour and parasitoid reproductive performance

The Asian parasitoid, Binodoxys communis (Gahan) (Hymenoptera: Braconidae), is a candidate for release against the exotic soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), in North America. In this study, we examined preferences by B. communis for the different developmental stages of A. glycines and investigated consequences of these preferences for parasitoid fitness. We also determined to what extent aphid defensive behaviours mediate such preferences. We found that B. communis readily attacks and successfully develops in the different A. glycines developmental stages. Binodoxys communis development time gradually increased with aphid developmental stage, and wasps took longest to develop in alates. An average (+/-SE) of 54.01+/-0.08% of parasitized A. glycines alatoid nymphs transformed into winged adult aphids prior to mummification. No-choice assays showed a higher proportion of successful attacks for immature apterous A. glycines nymphs compared to adults and alatoid nymphs. Also, choice trials indicated avoidance and lower attack and oviposition of adults and alatoid nymphs. The different aphid stages exhibited a range of defensive behaviours, including body raising, kicking and body rotation. These defenses were employed most effectively by larger aphids. We discuss implications for the potential establishment, spread and biological control efficacy of A. glycines by B. communis in the event that it is released in North America.     

Development and parasitism by Aphelinus certus (Hymenoptera: Aphelinidae), a parasitoid of Aphis glycines (Hemiptera: Aphididae)

Since its introduction in 2000, the soybean aphid (Aphis glycines Matsumura) has been a serious pest of soybean in North America. Currently, insecticide application is the only recommended control method. However, a number of natural enemies have the potential to regulate soybean aphid populations. In 2007, Aphelinus certus Yasnosh, a soybean aphid parasitoid native to Asia, was found in commercial soybean fields in Ontario. This is the first record of this species in North America. To evaluate the potential biological control services provided by A. certus for soybean aphid management, temperature-dependent developmental parameters and functional response to soybean aphid were determined. A. certus is capable of completing its development between temperatures of 15.3 and 30.2°C. The lower thresholds of development for the egg-mummy and mummy-adult life stages were determined to be 9.1 and 11.6°C, respectively. The lethal temperature of development for the egg-mummy and mummy-adult life stages were 29.5 and 31.0°C, respectively. In this temperature range, A. certus did not exhibit temperature-dependent mortality; however, parasitism rate increased with temperature. A. certus exhibited a type II functional response to the soybean aphid.     

Resistance of Glycine species and various cultivated legumes to the soybean aphid (Homoptera: Aphididae)

The soybean aphid, Aphis glycines Matsumura, is a new pest of soybean, Glycine max (L.) Merr., in North America. It has become widespread on soybean in North America since it was first identified in the Midwest in 2000. Species of Rhamnus L. (buckthorn) are the primary hosts of A. glycines, and soybean is known as a secondary host. There is limited information about the secondary host range of A. glycines. Aphid colonization on various legume hosts was compared in choice experiments. Aphid colonization occurred on species in the genus Glycine Wild. No colonization occurred on Lablab purpureus (L.) Sweet, Lens culinaris Medik, Phaseolus vulgaris L., Pisum sativum L., or species of Vicia L. and Vigna Savi. Colonization was limited or aphids were transient on species of Medicago L., Phaseolus L., and Trifolium L. There were significant differences in aphid colonization among Medicago truncatula accessions with numbers ranging from 7 to 97 aphids per plant. Six Glycine soja Sieb. & Zucc. accessions were as resistant as G. max accessions to A. glycines; these may represent novel sources of A. glycines resistance not found in G. max. Antibiosis was found to play a large role in the expression of resistance in three of the G. soja accessions. Results of this study indicated that G. max and G. soja were the best secondary hosts of A. glycines; however, its secondary host range may include other leguminous species. Therefore, A. glycines did not seem to have a highly restricted monophagous secondary host range.     

Characterization of antibiosis and antixenosis to the soybean aphid (Hemiptera: Aphididae) in several soybean genotypes

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is an introduced pest of soybean, Glycine max (L.) Merr., in North America, and it can reduce yields by 50%. Since 2000, when A. glycines was first detected in the United States, studies of this insect and possible control methods have been initiated. Plant resistance to this aphid species is one important component of integrated control. Reproduction of A. glycines was compared on 240 soybean entries in a pesticide-free greenhouse. Eleven entries had fewer nymphs produced, compared with the susceptible checks, and these entries were used in follow-up experiments to assess antibiosis and antixenosis. Antibiosis was estimated in true no-choice tests, in which adults were confined individually in double-sided sticky cages stuck to the upper side of leaves. Antixenosis was assessed in choice tests, in which all entries were planted in a single pot. Adult aphids were placed in the center of the pot, and 24 h later the number of adults on each plant was counted. Of the 11 entries evaluated, nine showed a moderate antibiotic effect to A. glycines, and the other two entries (K1639 and Pioneer 95B97) showed not only a strong antibiotic effect but also exhibited antixenosis as a category of resistance to A. glycines. The resistant soybean entries found in this work are potential sources for A. glycines control.     

基于MaxEnt模型的大豆蚜全球潜在地理分布分析

【目的】为预测和分析大豆蚜Aphis glycines的全球潜在地理分布,研究大豆蚜分布与环境变量之间的联系。【方法】利用最大熵法生态位模型(maximum entropy niche-based modeling, MaxEnt)和地理信息系统软件ArcGIS,根据收集的大豆蚜已知分布点和环境变量,预测大豆蚜的全球潜在地理分布区,推测环境变量对大豆蚜分布的影响。【结果】结果表明,大豆蚜适生区主要分布在低海拔地区,高 度适生区集中在25°~50°N的中国、日本、韩国、朝鲜、加拿大、美国、意大利和格鲁吉亚。决定大豆蚜分布地点的关键环境变量为最暖季度降水量、最暖季度平均温度、最湿季度平均温度、最干月降水量、月平均昼夜温差和温度季节性变化标准差。【结论】大豆蚜潜在地理分布区域广泛,应在各国大豆农产品贸易时做好检验检疫工作,以防止大豆蚜的扩散。     

Soybean aphid and soybean cyst nematode interactions in the field and effects on soybean yield

How above- and belowground plant pests interact with each other and how these interactions affect productivity is a relatively understudied aspect of crop production. Soybean cyst nematode, Heterodera glycines Ichinohe, a root parasite of soybean, Glycine max (L.) Merr., is the most threatening pathogen in soybean production and soybean aphid, Aphis glycines Matsumura, an aboveground phloem-feeding insect that appeared in North America in 2000, is the key aboveground herbivore of soybean in the midwestern United States. Now, both soybean aphid and soybean cyst nematode co-occur in soybean-growing areas in the Upper Midwest. The objectives of this study were to examine aphid colonization patterns and population growth on soybean across a natural gradient of nematode density (range, approximately 900 and 27,000 eggs per 100 cm3 soil), and to investigate the effect of this pest complex on soybean productivity. Alate (winged) soybean aphid colonization of soybean was negatively correlated to soybean cyst nematode egg density (r = -0.363, P = 0.0095) at the end of July, at the onset of peak alate colonization. However, both a manipulative cage study and openly colonized plants showed that soybean cyst nematode density below ground was unrelated to variation in aphid population growth (r approximately -0.01). Based on regression analyses, soybean aphids and cyst nematodes had independent effects on soybean yield through effects on different yield components. High soybean cyst nematode density was associated with a decline in soybean yield (kg ha(-1)), whereas increasing soybean aphid density (both alate and apterous) significantly decreased seed weight (g 100 seeds(-1)).     

Decline of soybean aphid (Homoptera: Aphididae) egg populations from autumn to spring on the primary host, Rhamnus cathartica

Soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae), is a severe pest of soybeans in North America. Soybean aphid populations cycle between a secondary summer host, where populations reproduce parthenogenetically and a primary host, where populations overwinter as eggs. In North America, the secondary host is soybean, and the primary hosts are Rhamnus cathartica L. (Rhamnaceae) and R. alnifolia L'Her. A location with abundant populations of soybean aphid on R. cathartica was identified near Guelph, Ontario, Canada, in October 2004, and eggs on trees were counted at multiple sites within that location each autumn and spring over the next 2 yr. Dynamics of naturally occurring soybean aphid populations on the primary host were assessed with respect to (1) decline of overwintering eggs from autumn to spring, (2) development of spring populations on R. cathartica, and (3) development of soybean aphid populations on soybean immediately adjacent to overwintering sites. Counts of aphid eggs declined by approximately 70% between autumn and spring sampling periods in 2004-2005. Significant differences in counts of aphid eggs relative to sampling height were observed in the canopy of R. cathartica. No edge effects were observed in the development of soybean aphid populations in soybeans adjacent to overwintering sites in this study. Very few eggs were collected at the same study location in the autumn of 2005, and no aphid eggs were collected from samples taken in the spring of 2006. Egg counts taken in the autumn of 2006 were intermediate in number relative to counts taken in the autumn of 2004 and 2005.     

Alfalfa living mulch advances biological control of soybean aphid

Despite evidence for biological control in North America, outbreaks of the invasive soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), continue to occur on soybean (Glycine max L. Merr.). Our objectives were to determine whether natural enemies delay aphid establishment and limit subsequent population growth and whether biological control can be improved by altering the within-field habitat. We hypothesized that a living mulch would increase the abundance of the aphidophagous community in soybean and suppress A. glycines establishment and population growth. We measured natural enemy and A. glycines abundance in soybean grown with and without an alfalfa (Medicago sativa L.) living mulch. Soybean grown with an alfalfa living mulch had 45% more natural enemies and experienced a delay in A. glycines establishment that resulted in lower peak populations. From our experiments, we concluded that the current natural enemy community in Iowa can delay A. glycines establishment, and an increase in aphidophagous predator abundance lowered the rate of A. glycines population growth preventing economic populations (i.e., below the current economic threshold) from occurring. Incorporation of a living mulch had an unexpected impact on A. glycines population growth, lowering the aphids' intrinsic rate of growth, thus providing a bottom-up suppression of A. glycines. We suggest future studies of living mulches or cover crops for A. glycines management should address both potential sources of suppression. Furthermore, our experience suggests that more consistent biological control of A. glycines may be possible with even partial resistance that slows but does not prevent reproduction.     

Resistance to Aphis glycines (Hemiptera: Aphididae) in various soybean lines under controlled laboratory conditions

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), a pest of soybean, Glycine max (L.) Merr., native to Asia, has recently become a principal pest of this crop in many areas of North America. Insecticides are currently used to manage A. glycines, but host plant resistance is a potential alternative management tool. Tests were conducted to determine resistance to A. glycines among soybean lines. 'Cobb,' 'Tie-feng 8,' and 'Jackson' were resistant to population growth of A. glycines compared with 'Cook' and '91B91,' a susceptible control. Antibiosis was evident in Cobb, Jackson, and Tie-feng 8 from lowered survival of first generation A. glycines, and in Cobb, Jackson, Tie-feng 8, and 'Braxton' from diminished reproduction by first generation aphids. Antixenosis was apparent in Cobb and Jackson during initial infestation of aphid population growth tests, because A. glycines were unsettled and dispersed readily from placement points on unifoliolate leaves. Decreased nymphiposition by A. glycines occurred on Cobb and Jackson, and it may have been caused by antibiotic chemicals in these lines, failure of aphids to settle, or both. Differences in distribution of A. glycines between unifoliolate leaves and other shoot structures suggest that unifoliolate leaves were acceptable feeding sites on 91B91 and Cook, whereas unifoliolate leaves and other shoot structures were roughly equally acceptable feeding sites on Braxton, Tie-feng 8, Jackson, and Cobb. However, Jackson and Cobb had relatively low counts of A. glycines on shoots that may have been due to abandonment of plants by aphids, decreased aphid survival, or both. Results confirm earlier findings that Jackson is a strong source of resistance to A. glycines, and they suggest that Tie-feng 8, Braxton, and especially Cobb are potentially useful sources of resistance.     

Population dynamics of soybean aphid and biotic mortality at the edge of its range

The soybean aphid, Aphis glycines Matsumura, was introduced to north central North America from Asia in 2000, and it has become a major pest of soybean, Glycine max (L.) Merr. Understanding how natural enemies impact aphid populations in the field is an important component in developing a comprehensive management plan. We examined the impact of naturally occurring predators in the field by using exclusion cages during July-August 2004 and 2005. Field cages of different mesh diameters were used to exclude different sizes of natural enemies from aphid-infested plots. Plots were surveyed twice weekly for A. glycines and natural enemies. Densities were recorded. Cage effects on mean temperature and soybean growth were found to be insignificant. Significant differences in aphid density were found between treatments in both years of the study (2004 and 2005); however, aphid densities between years were highly variable. Orius insidiosus (Say) was the most commonly occurring predator in the field. Other natural enemies were present in both years but not in high numbers. Parasitoids were present in both years, but their numbers did not suppress aphid densities. Treatment differences within years were related to the abundance of natural enemies. The large differences in aphid abundance between years were associated with the higher number of O. insidiosus found in the field in 2005 (416 total O. insidiosus) than in 2004 (149 total O. insidiosus). This study suggests that naturally occurring predators, primarily O. insidiosus, can have a large impact on A. glycines populations when predator populations are established before initial A. glycines colonization.     

An aphid-dip bioassay to evaluate susceptibility of soybean aphid (Hemiptera: Aphididae) to pyrethroid, organophosphate, and neonicotinoid insecticides

Since the discovery of the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), in North America in 2000, chemical control has been the most effective method to manage aphid outbreaks. Increased insecticide use in soybean raises the possibility of developing insecticide resistance in soybean aphid, and monitoring insecticide susceptibility is essential to maintain pesticide tools. We developed a simple and reliable aphid-dip bioassay by using a tea strainer that resulted in -90% survival in controls. Using this technique, we tested susceptibility of a greenhouse strain of soybean aphid that has never been exposed to insecticides, and field-collected aphid strains from two counties in Michigan. Aphid susceptibility was tested for five insecticides by dipping groups of five aphids in each insecticide dose for 10 s. After 48 h, aphids were classified as dead or alive, and counted. Aphids from all strains were highly susceptible to chlorpyrifos, lambda-cyhalothrin, esfenvalerate, and dimethoate, with LC50 and LC90 values well below the recommended application rates. However, aphids showed less susceptibility after 48 h to neonicotinoid imidacloprid, with higher LC90s and wider fiducial limits. This illustrated the potential limitation of using a 48-h assay to evaluate insecticides with longer-term, sublethal impacts. Nevertheless, this study made use of a simple aphid-dip method to test and compare insecticide susceptibility of soybean aphid. In the event of a field failure, the aphid populations involved can be tested in comparison to a susceptible greenhouse strain to determine the extent of resistance development.     

Soybean plant stage and population growth of soybean aphid

The soybean aphid, Aphis glycines Matsumura, is a newly invasive species of aphid in North America. Previous studies disagree as to whether soybean, Glycine max (L.) Merr., plant stage has an impact on aphid intrinsic rate of increase. Therefore, the growth rate of soybean aphids on soybean plants of different stages was examined at two different scales in the field. A planting date experiment was used to measure the population growth of soybean aphids on plants of different stages. Clip-cages were used to measure life history characteristics of individual aphids on plants of different stages. No differences were found in the population growth or dynamics of soybean aphids in the planting date experiment. The life history characteristics of individual aphids also showed no significant difference when feeding on different growth stages of soybean plants. The impact of these findings on soybean aphid management is discussed and the possible reasons why the results differ from previous estimates of the aphid growth-plant stage relationship are considered.     

Sugar feeding by the aphid parasitoid Binodoxys communis: how does honeydew compare with other sugar sources?

Parasitoids commonly forage in agricultural settings where the predominant sugar source is homopteran honeydew. The aphidiine braconid, Binodoxys communis, is an Asian parasitoid currently being released against the soybean aphid, Aphis glycines, in North American soybean fields. We conducted a number of laboratory experiments evaluating the quality of A. glycines honeydew as a sugar source for this parasitoid. Wasps readily fed on droplets of A. glycines honeydew, honey and 50% sucrose solution, but the length of feeding bouts on honey was significantly longer than on the other foods. Parasitoids lived significantly longer when fed honey or sucrose than honeydew, while starved wasps had the shortest lifespan. At 21+/-1 degrees C and 25+/-5% R.H., male B. communis that were fed honey lived for a maximum of 14 days, while females lived up to 20 days. Honeydew-fed wasps of both sexes lived approximately 3 days on average, which was 2-3 times longer than when they were only allowed access to water. Anthrone tests of whole insects showed that total sugar and glycogen levels of honey or sucrose-fed individuals were consistently higher than those fed honeydew or water. The glycogen levels of honeydew-fed wasps increased significantly after one day of feeding. HPLC analyses revealed that B. communis readily assimilates A. glycines honeydew oligosaccharides such as erlose, while others (e.g., raffinose) did not degenerate. Raffinose was present in much higher amounts in honeydew-fed wasps than in wasps fed other diets, so this sugar could be used as a 'signature' sugar for this species. Honeydew-fed wasps also had significantly lower fructose/(fructose+glucose) ratios than those from other diet treatments. Although A. glycines honeydew might be the main carbohydrate source within a soybean field, other sugar sources such as floral nectar appear to be more optimal foods for B. communis from a physiological standpoint. We discuss the results from the perspective of classical biological control of the soybean aphid in North America.     

Development of soybean aphid genomic SSR markers using next generation sequencing

Simple sequence repeats (SSRs) or microsatellites are very useful molecular markers, owing to their locus-specific codominant and multiallelic nature, high abundance in the genome, and high rates of transferability across species. The soybean aphid (Aphis glycines Matsumura) has become the most damaging insect pest of soybean (Glycine max (L.) Merr.) in North America, since it was first found in the Midwest of the United States in 2000. Biotypes of the soybean aphid capable of colonizing newly developed aphid-resistant soybean cultivars have been recently discovered. Genetic resources, including molecular markers, to study soybean aphids are severely lacking. Recently developed next generation sequencing platforms offer opportunities for high-throughput and inexpensive genome sequencing and rapid marker development. The objectives of this study were (i) to develop and characterize genomic SSR markers from soybean aphid genomic sequences generated by next generation sequencing technology and (ii) to evaluate the utility of the SSRs for genetic diversity or relationship analyses. In total 128 SSR primer pairs were designed from sequences generated by Illumina GAII from a reduced representation library of A. glycines. Nearly 94% (120) of the primer pairs amplified SSR alleles of expected size and 24 SSR loci were polymorphic among three aphid samples from three populations. The polymorphic SSRs were successfully used to differentiate among 24 soybean aphids from Ohio and South Dakota. Sequencing of PCR products of two SSR markers from four aphid samples revealed that the allelic polymorphism was due to variation in the SSR repeats among the aphids. These markers should be particularly useful for genetic differentiation among aphids collected from soybean fields at different localities and regions. These SSR markers provide the soybean aphid research community with the first set of PCR-based codominant markers developed from the genomic sequences of A. glycines.     

Effect of parasitism on flight behavior of the soybean aphid, Aphis glycines

Many aphid species possess wingless (apterous) and winged (alate) stages, both of which can harbor parasitoids at various developmental stages. Alates can either be parasitized directly or can bear parasitoids eggs or larvae resulting from prior parasitism of alatoid nymphs. Winged aphids bearing parasitoid eggs or young larvae eventually still engage in long-distance flights, thereby facilitating parasitoid dispersal. This may have a number of important implications for biological control of aphids by parasitoids. In this study, we determined the effect of parasitism by Aphelinus varipes (Hymenoptera: Aphelinidae) on wing development and flight of the soybean aphid, Aphis glycines (Hemiptera: Aphididae). We also quantified the influence of aphid flight distance on subsequent A. varipes development. Parasitism by A. varipes was allowed at different A. glycines developmental stages (i.e., alatoid 3rd and 4th-instar nymphs, alates) and subsequent aphid flight was measured using a computer-monitored flight mill. Only 35% of aphids parasitized as L3 alatoid nymphs produced normal winged adults compared to 100% of L4 alatoids. Flight performance of aphids parasitized as 4th-instar alatoid nymphs 24 or 48 h prior to testing was similar to that of un-parasitized alates of identical age, but declined sharply for alates that had been parasitized as 4th-instar alatoid nymphs 72 and 96 h prior to testing. Flight performance of aphids parasitized as alate adults for 24 h was not significantly different from un-parasitized alates of comparable ages. Flight distance did not affect parasitoid larval or pupal development times, or the percent mummification of parasitized aphids. Our results have implications for natural biological control of A. glycines in Asia and classical biological control of the soybean aphid in North America.     

Efficacy and nontarget effects of reduced-risk insecticides on Aphis glycines (Hemiptera: Aphididae) and its biological control agent Harmonia axyridis (Coleoptera: Coccinellidae)

The efficacy of three reduced-risk insecticides (pyrethrins, insecticidal soap, and narrow-range mineral oil) was determined for nymphs and adults of the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), an exotic pest of North American soybean, Glycine max (L.) Merr. These insecticides also were evaluated for nontarget effects on one of the aphid's key biological control agents, multicolored Asian lady beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), including first and third instars, pupae, and adults. A Potter Spray Tower was used to conduct direct spray laboratory bioassays. Results indicated that although pyrethrins and narrow-range mineral oil caused 100% mortality to A. glycines nymphs and adults at 72 h posttreatment, insecticidal soap caused equivalent mortality to only the nymphs during the same time period. However, A. glycines adult mortality due to the insecticidal soap (83.3%) was significantly greater than the control. Pyrethrins were highly toxic to first instars of H. axyridis (98% mortality), but they had no effect on third instars, pupae, or adults. Mineral oil and insecticidal soap were moderately lethal to first (48.9 and 40% mortality, respectively) and third (31.9 and 38.8% mortality, respectively) instars of H. axyridis, but they had no effect on pupae and adults. Our results suggest that pyrethrins, insecticidal soap, and narrow-range mineral oil may prove useful for soybean aphid management in organic soybean due to efficacy against the aphid with differential nontarget effects on select stages of H. axyridis. Additional studies will be necessary to elucidate the efficacy of these insecticides under field conditions.     

Seasonal phenology of Aphis glycines (Hemiptera: Aphididae) and other aphid species in cultivated bean and noncrop habitats in Wisconsin

The occurrence of aphid-transmitted viruses in agricultural crops of the Midwest and northeastern United States has become more frequent since the arrival and establishment of the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae). A. glycines is a competent vector of plant viruses and may be responsible for recent virus epidemics in Wisconsin snap bean, Phaseolus vulgaris L., fields. To determine whether vegetation surrounding crop fields could serve as sources of virus inocula, we examined the settling activity ofA. glycines and other aphid species in agricultural crops and noncrop field margins adjacent to snap bean fields. Noncrop field margins were made up of numerous virus-susceptible plant species within 10 m from snap bean field edges. During summers 2006 and 2007, horizontal pan traps were placed in commercial soybean [Glycine max (L.) Merr.], snap bean, and surrounding field margins to characterize aphid flight activity patterns in the different habitat types. Alate abundance and peak occurrence across years varied between crop and noncrop field margins and differed among patches of plants in field margins. Overall aphid activity peaked late in the season (21 August in 2006 and 28 July in 2007); with the majority (52%) of total aphids trapped in all habitats being A. glycines. Susceptibility to viral infection and confirmed visitation of A. glycines to these forage plants suggests the importance ofnoncrop habitats as potential sources of primary virus inoculum. Viral disease onset followed peak aphid flights and further implicates A. glycines as a likely vector of viruses in commercial bean and other crops in Wisconsin.     

Population dynamics of Aphis glycines (Homoptera: Aphididae) and impact of natural enemies in northern China

Field surveys of soybean aphid, Aphis glycines Matsumura, and its natural enemies, as well as natural enemy exclosure experiments, were conducted during 2003 and 2004 in soybean fields near Langfang, China. In 2003, aphid density increased six-fold during 12 d in July from 66+/-12 per 10 plants to a seasonal peak of 401+/-79 per 10 plants. Aphid density remained high for another 10 d and declined during late July and early August. In 2004, aphid density increased 29-fold during 13 d in July from 14+/-2 per 10 plants to a seasonal peak of 375+/-30 per 10 plants. Unlike 2003, aphid density remained relatively high during late July and August, peaking again at 296+/-31 per 10 plants on 24 August. In both years, aphid density remained below economic injury level and seemed to be limited by natural enemies. Exclosure of natural enemies led to increases in A. glycines density in 2003 and 2004. In 2003, peak aphid densities in large- and medium-mesh cages were three- and seven-fold higher, respectively, than densities on uncaged plants. In 2004, peak aphid densities in large- and medium-mesh cages were 2-fold and 30-fold higher, respectively, than densities on uncaged plants in one experiment. In another experiment, peak aphid densities in large-, medium-, and small-mesh cages were 8-fold, 28-fold, and 68-fold higher, respectively, than densities on uncaged plants. Both predators and parasitoids were important in limiting aphid density. We compare our results with those from North America and discuss implications for biological control.     

Tracking the role of alternative prey in soybean aphid predation by Orius insidiosus: a molecular approach

The soybean aphid, Aphis glycines (Hemiptera: Aphididae), is a pest of soybeans in Asia, and in recent years has caused extensive damage to soybeans in North America. Within these agroecosystems, generalist predators form an important component of the assemblage of natural enemies, and can exert significant pressure on prey populations. These food webs are complex and molecular gut-content analyses offer nondisruptive approaches for examining trophic linkages in the field. We describe the development of a molecular detection system to examine the feeding behaviour of Orius insidiosus (Hemiptera: Anthocoridae) upon soybean aphids, an alternative prey item, Neohydatothrips variabilis (Thysanoptera: Thripidae), and an intraguild prey species, Harmonia axyridis (Coleoptera: Coccinellidae). Specific primer pairs were designed to target prey and were used to examine key trophic connections within this soybean food web. In total, 32% of O. insidiosus were found to have preyed upon A. glycines, but disproportionately high consumption occurred early in the season, when aphid densities were low. The intensity of early season predation indicates that O. insidiosus are important biological control agents of A. glycines, although data suggest that N. variabilis constitute a significant proportion of the diet of these generalist predators. No Orius were found to contain DNA of H. axyridis, suggesting intraguild predation upon these important late-season predators during 2005 was low. In their entirety, these results implicate O. insidiosus as a valuable natural enemy of A. glycines in this soybean agroecosystem.     

基于吸虫塔（Suction Trap）的蚜虫测报预警网络的构建

吸虫塔（suction trap）是用来监测麦类蚜虫和大豆蚜Aphis glycines迁飞种群动态的大型植保测报设备,在欧洲和北美洲已经呈网络安装分布,为蚜虫的预警和防控提供重要依据。作者借鉴欧美吸虫塔的工作原理和设计,设计并生产了符合我国地域特征的吸虫塔设备,在东北、华北、华中、华东、西北等地布点安装了21台,用于监控我国麦类蚜虫和大豆蚜的迁飞动态,初步形成覆盖我国小麦主产区和大豆主产区的吸虫塔网络系统。此吸虫塔总高8.8m,由底部轴流风机运转产生的负压在塔顶部形成吸力,将迁飞经附近的小型昆虫吸入塔管,最后落入下部的样品收集瓶中,以此获得其迁飞的动态数据。吸虫塔网络的构建和完善,不仅为麦类蚜虫和大豆蚜的监控提供支撑,同时也为其它小型迁飞性昆虫监测、种群动态、生物多样性、生物信息学等研究提供数据。