播期对大豆蚜及其天敌种群动态的影响

【目的】研究大豆播期对大豆蚜Aphis glycines Matsumura及其天敌的影响。【方法】试验在2012年、2013年进行,设置了3个大豆播期处理。每周调查播期处理田大豆蚜种群及天敌种类和数量,分析大豆蚜种群数量、种群增长率的时序动态、大豆蚜和天敌的关联度。【结果】不同播期条件下大豆蚜有翅蚜及无翅蚜的种群动态趋势基本一致,有翅蚜蚜量高峰期要早于无翅蚜1周。处理间的大豆蚜田间始见期与终见期随着播期推后而延迟,大豆蚜在田间扩散和消退的时期也随着大豆播期延后。晚播的两个处理高峰期蚜量多于或等于正常播期处理的蚜量。大豆蚜与天敌关联度随着播期的推后而变高。在调查的7种天敌中大豆蚜与异色瓢虫的关联度最高,草蛉、小花蝽和蚜茧蜂也表现较高的关联度。【结论】播期会显著影响大豆蚜的田间始见期和终见期,随着播期的推迟大豆蚜种群高峰期蚜量以及大豆蚜与天敌的关联度都会提高。     

大豆蚜Aphis glycines Matsumura的研究

大豆蚜在我国主要大豆产地都有分布, 以吉、辽、黑和内蒙自治区的一部分为害最重, 为猖獗发生区。大豆蚜的寄主植物除大豆外, 还有野生大豆和鼠李, 由调查和接种试验的结果, 肯定了大量地分布在东北三省的鼠李为越冬寄主。 大豆蚜的全年发生周期和为害特点在大豆上共分三个阶段:1)从侵害豆苗起到7月中旬大豆盛花期止, 是大豆蚜的盛发时期, 占有总蚜量的50—70%, 群聚于豆株上部幼嫩的枝叶上, 这时期的为害, 对大豆的生长威胁最大;2)到7月下旬, 由于大豆生长点停止生长, 大豆蚜即从群聚于植株上部发生转移到分散在中、下部的叶片背面, 并同时出现小型蚜, 生长迟缓, 为田间大豆蚜为害的消退阶段;3)8月下旬结荚后期到9月上旬黄熟期, 重新开始了大豆蚜的后期繁殖阶段, 随即在秋末季迁回鼠李, 经雌雄交配产卵越冬, 秋季雄性蚜和雌性产卵蚜分别发生在不同的寄主上, 雌性发生在鼠李上, 雄性发生在大豆上。全年在大豆上共繁殖15代。 根据大豆蚜的生活规律和几年来田间消长规律并结合几年的气象资料综合分析的结果, 初步得出大豆蚜的发生消长规律和其影响因子:1)上年越冬量及早期田间蚜量大, 因而造成了苗期大发生;2)6月下旬至7月上旬的旬平均温度在22—25℃, 相对湿度在78%以下时, 则极有利于田间大豆蚜的发育和繁殖, 即使早期蚜量少, 由于繁殖快, 往往也能造成7月花期的大发生;3)7月底开始随着大豆生长点的停止生长, 由于营养条件的恶化, 造成了大豆蚜的消退阶段。 综合上述, 我们可以根据大豆蚜的越冬数量、气象预报、历年的蚜情资料和当年的蚜情调查, 做出长期或短期的蚜情预报。 防治方法, 从几年的室内外试验和大面积试验结果, 0.5%666、6%可湿性666300—400倍、E605 15000倍、烟草冰100倍液以及20% 666拌种都具有良好的毒杀作用, 其中0.5%666粉和20%666 以种子量的0.7%用药量拌种已广泛推广应用于生产。     

药剂包衣对苗期大豆蚜防治效果与安全性评价

【目的】大豆蚜Aphis glycines(Matsumura)是大豆上最重要的害虫之一。传统控制大豆蚜虫仍然以达到防治指标时大量喷洒化学药剂为主,危害人畜和环境安全。只有在大豆蚜发生初期进行有效防控,使其田间种群不能及时顺利的建立,从而实现无公害绿色防控。【方法】对筛选出的3种内吸式杀虫剂按不同浓度拌种包衣进行大田小区试验,调查分析包衣处理对大豆蚜、天敌以及大豆田其他害虫的影响和控制作用,同时对包衣处理后的大豆安全性、产量和品质进行评估。【结果】药剂拌种包衣处理能够显著压低苗期大豆蚜虫口基数,2014年对照区与处理区蚜量最高峰值比值最大达到448.15;同时对苗期大豆田间的双斑萤叶甲Monolepta hieroglyphica(Motschulsky)有很好的控制作用,处理区与对照区的受害株率差异极显著;并且保护了自然天敌种群;药剂拌种包衣处理在显著增产的同时还有效提升了大豆品质;经权威检测,收获后的籽粒在检出限内无药剂残留。【结论】药剂拌种包衣处理能有效控制苗期大豆蚜,不杀伤天敌,安全、无毒、无残留,而且增产显著,是比较理想的轻简无公害防控手段。     

黑龙江省哈尔滨地区吸虫塔有翅蚜种群动态

【目的】明确吸虫塔对作物蚜虫防控的指导意义,明确中国黑龙江省哈尔滨地区有翅蚜(和大豆蚜)的种群动态,为大豆蚜虫防控提供预警信息。【方法】2009至2012年通过吸虫塔监测哈尔滨地区有翅蚜及有翅大豆蚜动态结合当年田间大豆蚜动态调查。【结果】哈尔滨吸虫塔全年收集有翅蚜量为0.6~1.7万头不等。具1~3个高峰(不同年份有翅蚜发生高峰数量不同),高峰期时间1个月左右,位于7月中旬至10月中旬之间。周有翅蚜量达200头时预示着有翅蚜高峰期的到来,高峰期有翅蚜量可占年有翅蚜量的90%以上。同一地区不同年份有翅蚜高峰期时间不同。吸虫塔有翅大豆蚜亦具1~3个高峰期,时间位于当年有翅蚜的高峰期时间内,为短短的1周或几周,高峰期蚜量占全年采集有翅大豆蚜量的80%~95%。田间大豆蚜只存在一个高峰,2009、2010、2012年田间大豆蚜高峰期均与吸虫塔收集的大豆蚜高峰期相重叠,且峰值日期一致。【结论】吸虫塔可以很好地反应当年田间大豆蚜的种群动态,表现在高峰期及高峰点的预测,可为大豆蚜的预测预报提供预警信息。     

大豆蚜对环境的适应及对大豆产量的影响

2009-2010年,以辽东山区大豆主产区岫岩县作为试验点,系统调查了大豆蚜Aphis glycines Matsumura正常型蚜和小型蚜的种群动态,研究了蜡蚧轮枝菌Verticillium lecanii(Zimmerman)Viegas、豆柄瘤蚜茧蜂Lysiphlebus fabarum Marshall、异色瓢虫Harmonia axyridis(Pallas)对大豆蚜正常型蚜和小型蚜的寄生与捕食作用;另外,也研究了降雨对小型蚜和正常型蚜的冲刷作用,以及小型蚜对大豆产量的影响等。研究结果表明,7月上中旬为大豆蚜小型蚜发生初期,7月下旬—8月上旬为小型蚜发生高峰期,2010年小型蚜平均蚜量达10000头/百株以上。此外,通过比较大豆蚜正常型蚜和小型蚜排蜜量,发现正常型蚜与小型蚜在30min内的排蜜频率差异极其显著,正常型蚜排蜜次数明显多于小型蚜。蜡蚧轮枝菌对大豆蚜小型蚜的侵染较正常型低,前者被侵染率低于3%,后者被侵染率高达25%。豆柄瘤蚜茧蜂对正常型蚜的寄生率较小型蚜高,寄生率分别为43.41%和0.58%。异色瓢虫3龄幼虫对正常型蚜和小型蚜的捕食率分别为80.24%和36.36%。降雨对小型蚜冲刷作用明显低于正常型蚜。最后,通过对单株蚜量与单株产量进行单因素方差分析,结果表明,单株小型蚜量对产量影响不显著(F=0.378;df=7,1;P>0.05)。上述研究为明确大豆蚜的发生与为害、小型蚜适应环境的生存机制以及自然天敌对大豆蚜的田间控制作用,进而为大豆蚜的可持续控制提供理论依据。     

黑龙江大豆蚜种群动态及田间空间分布研究

2007-2009年对黑龙江大豆蚜田间种群动态的调查结果表明,6月中旬大豆蚜Aphis glycines Matsumura开始在田间出现,3～5周后田间有蚜株率达到100%。7月未至8月初蚜量达到高峰期,9月中下旬在田间逐渐消失。大豆蚜有翅蚜与无翅蚜的发生动态基本一致,有翅蚜高峰期有时会稍有提前。2007年大豆蚜发生时期早、基数大、增长周期长导致高峰期蚜量显著高于2008年和2009年。大豆蚜田间分布聚集度指标I﹥0、m*/m﹥1、Ca﹥0、C﹥1,整个生长季种群都表现为聚集分布。建立的Iwao回归关系方程(m*=7.14758+1.11200m)表明种群分布的基本成分为个体群,个体之间表现为相互吸引。     

东北大豆生态区捕食性食蚜蝇种类及其对大豆蚜的控害效应分析

食蚜蝇是蚜虫的主要天敌之一。通过对东北大豆生态区捕食性食蚜蝇的种类和种群数量调查,共发现9属15种捕食性食蚜蝇,其中,黑带食蚜蝇Episyrphus balteatus(De Geer)、大灰食蚜蝇Eupeodes corollae(Fabricius)、印度细腹食蚜蝇Sphaerophoria indiana(Bigot)和宽尾细腹食蚜蝇Sphaerophoria rueppelli(Wiedemann)为田间常见种;黑带食蚜蝇是大豆整个生长过程中的主要优势种,大灰食蚜蝇是大豆生长前期的优势种,细腹食蚜蝇是大豆生长中后期的优势种群;食蚜蝇幼虫发生高峰期与大豆蚜发生高峰期基本吻合。通过捕食量测定,发现黑带食蚜蝇平均每头幼虫对大豆蚜的理论最大捕食量为984头;在田间益害比为1∶150时,控害效果达到最大,近60%;而在1:250时单头控制蚜量最多,为102头,且控害效果可达到40%以上。以上研究结果表明,食蚜蝇对大豆蚜具有较强的捕食能力,具有很大的生防应用潜能。本文还提出了关于食蚜蝇田间保护的可行性措施。     

作物多样性对大豆蚜的控蚜效应

【目的】研究大豆蚜发生为害及大豆与多种作物间邻作种植对大豆蚜的控制作用,为大豆蚜的可持续综合治理提供理论依据。【方法】采用系统调查的方法,研究大豆蚜和天敌田间种群动态;通过田间罩笼、人工接蚜和释放天敌的方法,研究捕食性天敌对大豆蚜种群的控制作用;在佳木斯地区进行大豆与早熟马铃薯间作,牡丹江地区进行黄瓜-大豆-玉米、甜葫芦-大豆-玉米、烟草-大豆-香瓜、甜菜-大豆-玉米等多作物带状穿插种植模式,以单作大豆田为对照,对不同种植模式的大豆田大豆蚜与天敌进行调查,研究作物多样性对大豆蚜的控制作用。【结果】2009年6月中下旬大豆蚜开始侵入大豆田,3~5周后田间有蚜株率达到100%,大豆蚜种群发生高峰期在7月下旬至8月上旬,9月上旬在田间逐渐消失。草蛉、瓢虫和寄生蜂等为蚜虫天敌优势种;按大豆蚜与天敌数量之比700︰1,释放异色瓢虫和叶色草蛉成虫7 d后,蚜虫种群减退率分别为54.78%和78.79%;大豆与早熟马铃薯间作,在大豆蚜种群迅速增长期早熟马铃薯收获(7月20日)后第5天,豆田蚜虫天敌总数是收获前的2.6倍,与同期单作大豆田相比,间作田大豆蚜种群数量降低了51.3%。大豆与甜葫芦、香瓜、烟草和玉米等作物进行多样性间作种植,在大豆蚜田间发生高峰期,单作豆田益害比为1︰65.2,多样性种植区的大豆田益害比为1︰26~1︰42,与单作大豆田相比,间作田大豆蚜种群数量降低40.7%~83.5%。【结论】2009年大豆蚜的种群高峰期为8月3日,田间的天敌优势种类为草蛉、瓢虫和寄生蜂。早熟马铃薯与大豆间作,在大豆蚜种群迅速增长期间收获早熟马铃薯,大量蚜虫天敌转移至间作的大豆田,从而形成对大豆蚜的控制。大豆与其它经济作物间邻作,大豆田天敌昆虫与蚜虫的益害比明显提高,表明利用农田作物多样性能充分发挥自然天敌的生物控害作用。     

大豆蚜危害胁迫对大豆叶片几个重要生理指标的影响

大豆蚜Aphis glycines Matsumura是为害大豆(Glycine max)的重要害虫,已给我国大豆生产造成了较为严重的经济损失。本研究通过测定大豆蚜危害胁迫后大豆叶片可溶性蛋白、非可溶性蛋白、可溶性糖含量及2种防御性酶——过氧化物酶(POD)、过氧化氢酶(CAT)活性的动态变化,探讨大豆蚜危害胁迫对大豆叶片几个重要生理指标的影响。研究结果表明,受到大豆蚜危害胁迫的大豆叶片与未受为害叶片中所含可溶性蛋白含量存在极显著差异(t0.01=11.814,df=4,P<0.01),且前者较后者含量明显增高1.73mg·g-1。与之相比较,非可溶性蛋白与可溶性糖含量分别在此两处理间无显著差异(t0.05=-1.104,df=4,P>0.05;t0.05=-2.639,df=4,P>0.05)。此外,受到大豆蚜危害胁迫的大豆叶片较未受为害叶片中所含POD活性有所升高,但在两处理间POD活性无显著差异(t=-2.639,df=4,P>0.05)。同时,受到大豆蚜危害的大豆叶片较未受为害的大豆叶片中CAT活性增强。本研究有助于揭示大豆蚜对大豆的危害机理,评价不同大豆品种对大豆蚜虫危害的耐受程度,也为大豆抗虫品种选育以及大豆蚜的可持续控制提供理论依据。     

马铃薯-大豆、玉米-大豆邻作对大豆田主要刺吸式害虫以及其他害虫的种群动态影响

【目的】大豆蚜Aphis glycines(Matsumura)是危害我国大豆产量的重要刺吸式害虫,茄无网蚜Acyrthosiphon solani(Kaltenbach)是近年来在大豆田发生逐渐呈上升趋势的刺吸式害虫,蚜虫的发生动态严重影响大豆的产量和品质,本试验调查了马铃薯-大豆、玉米-大豆邻作种植模式对大豆田刺吸式害虫及其他主要害虫的种群动态的影响,为精准使用农药防控蚜虫提供依据。【方法】采用系统调查的方法,研究大豆田刺吸式害虫以及天敌的种群动态,在哈尔滨香坊农场进行马铃薯-大豆、大豆-玉米邻作的种植模式,对其大豆田中大豆蚜、茄无网蚜等刺吸式口器的害虫及天敌动态发生数量进行调查。【结果】2014年与2015年玉米-大豆、马铃薯-大豆种植模式的大豆田中的大豆蚜数量明显低于对照田,2014年玉米-大豆差异更显著,2015年马铃薯-大豆差异性显著。2014年与2015年玉米-大豆、马铃薯-大豆邻作种植模式的大豆田中的茄无网蚜数量显著低于对照田。而2014年8月温度低于2015年虫量相对高于2015年,虫量高时天敌总群动态也相对较高,达到调控作用。【结论】玉米-大豆、马铃薯-大豆邻作种植模式能够起到减少大豆蚜和茄无网蚜的为害的作用,并能够减少农药的使用量。     

What is the economic threshold of soybean aphids (Hemiptera: Aphididae) in enemy-free space?

Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is a serious pest of soybean, Glycine max (L.) Merr., in the North Central United States. Current management recommendations rely on the application of insecticides based on an economic threshold (ET) of 250 aphids per plant. Natural enemies are important in slowing the increase of aphid populations and can prevent them from reaching levels that can cause economic losses. However, biological control of A. glycines is inconsistent and can be affected negatively by the intensity of agricultural activity. We measured the impact of a natural-enemy-free environment on the capacity of the current ET to limit yield loss. In 2008 and 2009, caged microplots were assigned to one of three treatments: plants kept aphid-free (referred to as the control), plants that experienced a population of 250 aphids per plant (integrated pest management [IPM]), and plants that experienced unlimited aphid population growth (unlimited). The population growth rate of aphids in the unlimited treatment for the 10 d after the application of insecticides to the IPM treatment was calculated using linear regression. The linear equation was solved to determine the mean number of days between the ET and the EIL for an aphid population in absence of predators. The number of days was determined to be 6.97 +/- 1.11 d. The 2-yr average yield for the IPM treatment was 99.93% of the control treatment. Our study suggests the current soybean aphid ET of 250 aphids per plant can effectively protect yield even if the impact of natural enemies is reduced.     

Effect of soybean varieties on survival and fecundity of western corn rootworm

The western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is a major pest of corn (Zea mays L.) in North America and has evolved resistance to crop rotation by ovipositing in alternate crops such as soybeans [Glycine max (L.) Merr.]. Through experiments with plants grown in the greenhouse and the field, we tested whether soybeans with resistance to the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), affected survival, fecundity, and consumption of soybean for D. v. virgifera. Soybean varieties tested included those types resistant to A. glycines (Rag1 and rag1/rag3) and a susceptible near isoline of the Rag1 variety. Females were provided with a diet of corn tissue for 4 d after which they were fed a diet of tissue from one of three soybean varieties for 4 d, starved for 4 d, or fed corn tissue. When fed greenhouse grown plants, strains differed significantly in survival and consumption, but consumption did not differ by variety of soybean. Diet treatment only affected fecundity; individuals fed corn continuously had greater fecundity than those individuals fed soybeans. In the experiment with plants grown in the field, leaf consumption differed among strains and individuals fed corn continuously had greater fecundity than the other treatments. Soybean varieties with Rag1 and rag1/rag3 resistance to A. glycines did not appear to affect the fitness of D. v. virgifera. Thus, planting of these A. glycines-resistant soybean varieties should not directly affect the spread of rotation-resistant D. v. virgifera.     

An hrcU-homologous gene mutant of Xanthomonas campestris pv. glycines 8ra that lost pathogenicity on the host plant but was able to elicit the hypersensitive response on nonhosts.

Transposon mutagenesis was used to isolate nonpathogenic mutants of Xanthomonas campestris pv. glycines 8ra, which causes bacterial pustule disease in soybean. A 6.1-kb DNA region in which a mutation gave loss of pathogenicity was isolated and found to carry six open reading frames (ORFs). Four ORFs had homology with hrcU, hrcV, hrcR, and hrcS genes of Ralstonia solanacearum and X. campestris pv. vesicatoria. One nonpathogenic mutant, X. campestris pv. glycines H80, lost pathogenicity on soybean but was able to elicit the hypersensitive response (HR) on nonhost pepper and tomato plants. This mutant still multiplied as well as the wild type in the leaves or cotyledons of soybean. Although the DNA and amino acid sequences showed high homology with known hrp genes, the hrcU-homolog ORF is not required for HR induction on nonhost plants, pepper and tomato, or for the multiplication of bacteria in the host plant. This gene was only required for the pathogenic symptoms of X. campestris pv. glycines 8ra on soybean.     

Enumerative and binomial sequential sampling plans for soybean aphid (Homoptera: Aphididae) in soybean

Since the discovery of the soybean aphid, Aphis glycines Matsumura, in midwestern U.S. soybean, Glycine max L., in 2000, the aphid has become a significant economic pest. Basic information about estimating population density within fields is unknown. Therefore, we developed two sampling plans to efficiently characterize A. glycines densities. Enumerative and binomial sequential plans were developed using 89 data sets collected from 10 commercial fields sampled during 2001-2003. Re-sampling software was used to validate the enumerative plan on whole plant counts, based on Taylor's power law parameters (a = 9.157 and b = 1.543). For research applications, the enumerative plan was modified to provide an actual precision level of 0.10 (SE/mean), which resulted in an average sample number of 310 individual plants. For integrated pest management (IPM) purposes, we developed an enumerative plan with an actual precision of 0.25, which resulted in an average sample number of 38 individual plants. For IPM applications, the binomial plan will likely be more practical. Binomial plans were developed using two tally thresholds at five action thresholds. Final analysis of the operating characteristic curve for each plan indicated that the tally threshold of > or = 40 aphids per plant, and an action threshold of 0.837 (84% of the plants infested) provided the most correct treat (4%) and no-treat (95%) decisions, with very low incorrect treat (0.5%) and no-treat (0.5%) decisions. A tally threshold of > or = 40 aphids per plant and action thresholds of 84% of plants infested is equivalent to a mean density of 250 aphids per plant, a recently recommended economic threshold. Using this threshold, the minimum required sample number for the binomial plan was 11 plants.     

葱斑潜蝇防治指标及防治适期研究

研究表明葱斑潜蝇百株潜道 (X)与大葱产量损失率 (Y)之间呈显著的相关性 ,其相关回归式 :Y=-2 .8397+ 0 .0 30 4 8X。在大葱产量 30 0 0～ 6 0 0 0kg 6 6 7m2 时 ,经济允许损失率为 1 .4 7%～ 2 .94 % ,允许百株潜道为 1 4 1 .4～ 1 89.6条 ;防治指标拟定为百株潜道 1 5 0条。防治适期为成虫羽化高峰期至幼虫初孵期 ;大葱生育中、后期 ( 6～ 1 0月 )防治对于降低葱属作物的损失具有较大意义。药剂防治以含有阿维菌素的制剂和乐斯本效果较好。     

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.     

Forecasting seasonal population growth of Aphis glycines (Hemiptera: Aphididae) in soybean in Illinois

From 2001 to 2004, 252 fifty-plant samples were collected from commercial soybean, Glycine max L., fields in three townships (93-km2 area) in Illinois. Townships were sampled every 3 wk from late June or early July when aphids (Aphis glycines Matsumura) first invaded the townships to early August. We used linear regression of 18 mean township field densities to calibrate several simple models to predict the change in aphid population density in a township from one sampling date to the next. The best exponential model for the complete data set has an r2 = 0.54, Y2 = Ylexp (0.09659 x DAY), where Y1 and Y2 are the first and second samples of aphids separated by a 3-wk period (the number of days, DAY). Our intrinsic rate of increase for the population is much lower than rates calculated in other studies. The best single-variable linear model has an r2 = 0.88, Y2 = Y1 + 0.1084 x Y1 x DAY. The latter model indicates the value of including monitoring data in the prediction. The best two-variable model has an R2 = 0.98, Y2 = Y1 + 0.08136 x Y1 x DAY + 0.000080 x N1(2) x DAY, where N1(2) x DAY is the interaction term for initial, squared, sample density of the season multiplied by the number of days between samples. The latter two models indicate that the change in the population density is greater for more dense populations. Degree-days were generally inferior to days as the time component in the simple models.     

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.