The effect of an alternate weed host,hairy nightshade,Solanum sarrachoides (Sendtner) on green peach aphid distribution and Potato leafroll virus incidence in potato fields of the Pacific Northwest

Hairy nightshade, Solanum sarrachoides (Sendtner) is an annual solanaceous weed prevalent in potato farmlands of the Pacific Northwest. S. sarrachoides is also a reservoir for Potato leafroll virus (PLRV) and its most important vector, the green peach aphid, Myzus persicae (Sulzer). Green peach aphids prefer S. sarrachoides than potato, Solanum tuberosum (L.), and produce more nymphs on S. sarrachoides than on potato. Increased green peach aphid preference for S. sarrachoides and greater fecundity on this plant could lead to overcrowding and movement toward neighboring potato plants. To test our hypothesis, field trials were conducted at Kimberly, Idaho during the summers of 2003 and 2004. A row of S. sarrachoides seedlings was planted in the middle of potato plots and naturally occurring green peach aphid populations were monitored weekly on potato plots with and without S. sarrachoides. More aphids were consistently found on S sarrachoides plants than on potato plants. More aphids were found on potato plants in plots with S. sarrachoides plants than without S. sarrachoides. Targeted insecticide applications on S. sarrachoides rows alone reduced the number of aphids on potato plants in those plots, suggesting that insecticide sprays prevented aphid movement from S. sarrachoides to potato. Testing of potato tuber sprouts 90 days after harvest by double antibody sandwich ELISA indicated a greater PLRV infection rate on plots with S. sarrachoides than plots without S. sarrachoides. Therefore, the presence of S. sarrachoides in potato plots will likely increase aphid populations and PLRV incidence on neighboring potato plants.     

Rate of spread of PVYn by alateMyzus persicae (Sulzer) from infected to healthy plants under laboratory conditions

Summary Alate green peach aphids,Myzus persicae (Sulzer), tested in a flight chamber during their maiden flight period displayed behaviours ranging from repeated trivial flights to settling on the plants. The interaction of alate vector density and PVYⁿ spread was dichotomous, virus spread was significantly related to vector density in some trials but virus spread was nil or limited and not significantly dependent on vector density in others. The green peach aphid colony used in these experiments provided a mixture of active and highly active alate populations. Results suggest that inactive and active vectors came from the active and highly active alate populations, respectively. Therefore, winged aphids within a species cannot all be attributed the same vector efficiency unless known to originate from the same population. At a 15% inoculum level the intercept for the regression model for the spread of PVYⁿ was 5.03% indicating that there is a significant probability of propagation at aphid densities as low as one. However, over the range of aphid densities tested, the rate of spread per aphid was low, 0.08%, suggesting that reinfection of newly infected plants or movement interference between aphid vectors rapidly became important factors negatively affecting virus spread. Although these results cannot be directly transferred to field conditions they provide confirmation that lowM. persicae numbers can transmit unacceptable levels of mosaic and that low inoculum levels are required to decrease the risk of transmission by the small aphid numbers which cannot be realistically controlled.     

茶蚜趋色性及信息物质增进色板诱蚜效应研究

茶蚜广泛分布于我国茶区，刺吸危害茶树嫩梢。拟使用粘性色板诱捕之，减免施药。使用素馨黄、芽绿、土黄、桔黄、果绿、大红、纯白、紫色、湖蓝、天蓝、桃红和墨绿等12种粘性色板，经多年多点诱捕茶蚜，并在芽绿色板上附着不同种类和相互比例的茶梢信息物质引诱茶蚜。发现素馨黄和芽绿色彩对茶蚜的引诱力显著强于其它色彩，茶蚜具有显著的趋黄、绿习性；信息物质皆可增强色板对茶蚜的诱捕力，其中以C5、C6醇类、醛类和酯类等绿叶气味成分组成的混合物对色板增效作用最强，顺-3-己烯-1-醇次之、反-2-己烯醛和2-戊烯-1-醇又次之。认为：生长季节成蚜大量迁飞时使用携带绿叶气味诱芯的色板诱捕之，可有效压低其虫口密度。     

Constitutive emission of the aphid alarm pheromone, (E)-β-farnesene, from plants does not serve as a direct defense against aphids

Background  

The sesquiterpene, (E)-β-farnesene (EBF), is the principal component of the alarm pheromone of many aphid species. Released when aphids are attacked by enemies, EBF leads aphids to undertake predator avoidance behaviors and to produce more winged offspring that can leave the plant. Many plants also release EBF as a volatile, and so it has been proposed that this compound could act to defend plants against aphid infestation by 1) deterring aphids from settling, 2) reducing aphid performance due to frequent interruption of feeding and 3) inducing the production of more winged offspring. Here we tested the costs and benefits of EBF as a defense against the green peach aphid, Myzus persicae, using transgenic Arabidopsis thaliana lines engineered to continuously emit EBF.     

Genetic Resistances to Potato Leafroll Virus, Potato Virus Y, and Green Peach Aphid in Progeny ofSolanum etuberosum

Increasing prevalence of potato leafroll virus (PLRV) and potato virus Y (PVY) has been reported in seed and commercial potato production, resulting in the rejection of potatoes for certification and processing. Host plant resistance to PLRV and PVY and their primary vector, green peach aphid,Myzus persicae, could limit the spread of these viruses. Host plant resistance to PLRV, PVY, and green peach aphid has been identified in non-tuber-bearingSolanum etuberosum (PI 245939) and in its backcross 2 (BC₂) progeny. Resistance to green peach aphid involved a reduction in fecundity and adult aphid size. In addition, one BC₂ individual was identified as possessing a genetic factor that was detrimental to nymph survival. PVY resistance was identified in all five BC₂ progenies evaluated in a field screening under intense virus pressure. PLRV resistance was identified in two of the five BC₂ progeny. This resistance was stable in field and cage evaluations with large populations of viruliferous aphids. Based on the segregation of virus resistances in the BC₂ , PVY and PLRV resistances appear to result from the action of independent genetic mechanisms that reduce the levels of primary and secondary virus infection. Two BC₂ individuals, Etb 6-21-3 and Etb 6-21-5 were identified as having multiple resistances to PLRV, PVY, and green peach aphid derived fromS. etuberosum. This germplasm could prove useful to potato breeders in the development of virus-resistant cultivars.     

Acquisition of potato leafroll virus byMyzus persicae from secondarily-infected potato plants of different genotypes

Summary The acquisition of potato leafroll virus (PLRV) byMyzus persicae nymphs from the top leaves of potato plants was studied throughout a growing season in relation to the antigen titre in those leaves and the feeding behaviour of the aphid. Secondarily-infected plants of eight potato genotypes with different levels of field resistance served as virus sources. Early in the growing season, plants were efficient sources for virus acquisition. The amount of viral antigen detected inM. persicae nymphs fed on the top leaves was strongly correlated with the titres of viral antigen in these leaves. Virus acquisition from the top leaves of older potato plants was markedly impaired and could not be correlated with their virus titre. With increasing age of the potato plants and the development of virus symptoms, the virus titre in the leaves declined and the initial weak correlation between the virus titre and field resistance ratings disappeared. Thus, screening secondarily-infected potato plants for field resistance to PLRV based on the concentration of viral antigen in leaves or in aphids fed on them should be avoided later in the growing season. The feeding rate ofM. persicae, measured by the number of honeydew droplets excreted, did not account for the reduced uptake of virus from older plants since it was not influenced by the age of the plant. Throughout the growing season, the feeding rate ofM. persicae nymphs on PLRV-infected plants was higher on genotypes with low levels of field resistance to PLRV than on genotypes with high ones.     

噻虫嗪种子包衣对燕麦蚜虫和红叶病的控制效果及农药残留分析

红叶病是由蚜虫传播黄矮病毒(BYDV)引起的燕麦上的重要病害,有效防治蚜虫可控制燕麦红叶病的发生。为了明确噻虫嗪种衣剂的应用效果和安全性,通过田间试验研究了噻虫嗪种子包衣对燕麦蚜虫和红叶病的防效及持效期,并采用高效液相色谱法测定了药物在植株和籽粒上的残留动态。结果表明,种子包衣处理后,燕麦单株蚜量和红叶病病情指数均低于对照,苗期至拔节期的蚜虫防效为77.71%～87.91%,红叶病防效为65.79%～82.89%;孕穗期至扬花期的蚜虫防效为58.45%～68.61%,红叶病防效为62.98%～64.14%,持效期长达90 d,可实现一次施药减轻蚜虫为害、控制红叶病的效果。残留分析表明,噻虫嗪种衣剂在燕麦植株中的残留动态符合一级动力学方程C=13.218e-0.0971t,半衰期为7.14 d,播种后60～100 d残留量为0.43～9.86 mg·kg-1,接近或超过了现有的草料MRLs值,此时不宜作为青饲料;播种110 d以后残留量≤0.06 mg·kg-1,可刈割青饲料或作为干草贮存使用。在燕麦籽粒中未检测到噻虫嗪。     

马铃薯脱毒种薯原种基地评选条件的研究

摘要1988～1989年选择甘肃省20个条件各异的马铃薯脱毒种薯基地,研究评选优良原种基地的条件.结果认为,单纯用高纬度、高海拔、无霜期短、冷凉和多雨等传统非生物量度作评价有时失败.夏季黄皿诱来有翅蚜总量或有翅桃蚜总数、蚜虫种类丰盛度、蚜虫天敌丰盛度及植物多样性等是评价基地的最佳量度.     

Populations of aphids on named varieties of Irish potatoes

Populations of the green peach aphid,Myzus persicae (Sulzer), and the potato aphid,Macrosiphum euphorbiae (Thomas), were observed on 27 named varieties of Irish potatoes in the Yakima Valley of Washington intermittently from 1947 through 1968. The Epicure, Great Scot, and B5141-6 varieties produced relatively fewer green peach aphids than other varieties tested; Bliss Triumph and Red Pontiac produced relatively fewer potato aphids. Except for Doebay Red, the red-skinned varieties, Bliss Triumph, Red McLure, Norland, and Earnly Rose, were extremely to moderately productive of the green peach aphid. No correlation was apparent between abundance of aphids and the specific gravity or yield of tubers.     

Potato leafroll virus spread in differentially resistant potato cultivars under varying aphid densities

An action threshold of 3-10 green peach aphid,Myzus persicae (Sulzer), apterae per 100 lower leaves is recommended for use in Minnesota to prevent further spread of potato leafroll virus (PLRV) in potato,Solarium tuberosum L. This threshold was first developed and validated using the PLRV susceptible cultivar Russet Burbank. Here we report experiments to determine if higher aphid densities could be tolerated in PLRV resistant cultivars,i.e., Kennebec (moderately resistant) or Cascade (highly resistant), without an increase in PLRV infection. Insecticidal sprays were applied to plots when predetermined target aphid densities, based on number of apterae per 100 leaves, were reached: 3, 10, 30, and 100 (Russet Burbank); 10, 30, 100, and 300 (Kennebec); and 30, 100, 300, and 1000 (Cascade). The response variable was the average percentage of PLRV infected plants. Overall mean cumulative aphid-days and percent PLRV infection were 617 and 23.5% for Russet Burbank, 1,296 and 10.2% for Kennebec, and 4,816 and 9.5% for Cascade. For each cultivar, the highest target aphid density tolerated without an increase in PLRV spread was determined by comparing PLRV infection in plots sprayed on predetermined thresholds to PLRV infection in plots where aphids were rigorously controlled. This maximum density was 10 apterae per 100 leaves for Russet Burbank and 300 apterae per 100 leaves for Cascade. Results using Kennebec were ambiguous, but Kennebec was always more resistant to PLRV than Russet Burbank. Excised leaflet tests showed that the cultivars did not differ in resistance to green peach aphid. It appears that action thresholds based on green peach aphid apterae can be different depending upon the inherent PLRV-resistance of the cultivar.     

Resistance of potato clones to the green peach aphid and potato leafroll virus

During 1980 and 1981 potato cultivars and breeding selections, including cultivated species and their hybrid derivatives, were evaluated for resistance to the green peach aphid (GPA),Myzus persicae (Sulzer), and to potato leafroll virus (PLRV). Criteria used were the number of aphids which colonized the clones in free choice field experiments and the number of plants derived from these experiments which showed symptoms of PLRV infection. Generally, greater resistance to GPA was found inSolarium tuberosum gp.andigena selections and hybrids than in gp.tuberosum cultivars. There were approximately fourfold differences in season-mean GPA levels among the clones tested each year. Forty-two families, representing a cross-section of the USDA breeding populations at the University of Idaho Research and Extension Center, Aberdeen, showed a similar range in colonization levels. Resistance to GPA colonization appeared to be more prevalent in gp.andigena, gp.phureja, and gp.stenotonum derivatives. There was a weak positive correlation (r² = .34, P = .01) between foliar total glycoalkaloids and season-mean GPA colonization levels for six clones representing the range of observed resistance to GPA. Resistance to GPA colonization was apparently not directly related to resistance to PLRV infection. Katahdin, for example, was relatively susceptible to GPA colonization but very resistant to PLRV infection whereas selection A69657-4 (gp.andigena) was among the most resistant to GPA colonization but among the more susceptible to PLRV infection. Breeding for resistance to GPA colonization therefore may not be as promising for PLRV control as developing PLRV resistant cultivars.     

How Long can Rogued Potato Plants Left in the Field Be a Source of <Emphasis Type="Italic">Potato Virus Y</Emphasis> for Aphids?

Removal of diseased plants (roguing) is commonly practiced in seed potato production. Diseased plants left to desiccate in fields could possibly serve as sources of Potato virus Y (PVY). PVY acquisition by three aphid species (Myzus persicae, Rhopalosiphum padi, Aphis fabae) was evaluated with leaflets from rogued plants for seven days. Results showed greater PVY acquisition rates in non-colonizing aphids species compared to colonizing ones. The proportion of aphids leaving leaflets increased with time (i.e. days after plants were uprooted) and some aphids were carrying PVY in their stylets on each of the seven days of the experiment, suggesting that aphids were able to probe and acquire PVY even when plants wilted. These results confirmed that diseased plants left in fields can serve as a source of PVY for aphids even after they wilted and emphasises that proper actions must be taken to efficiently remove diseased plants from fields.     

Roquette,Eruca vesicaria subsp.sativa a good host for long-term maintenance of aphid vectors of potato viruses

Since 1971, we have used roquette,Eruca vesicaria (L.) Cav. subsp.sativa (Mill.) Thell., as a host for prolonged maintenance of colonies of the green peach aphid,Myzus persicae (Sulzer), and the potato aphid,Macrosiphum euphorbiae (Thomas). When roquette plants were kept in a growth chamber with 12 hour light and dark periods and a temperature regime of 20°C light and 15°C dark, or in greenhouse cubicles with temperatures ranging from 22–28°C and light periods ranging from 12 to 14 hours, colonies of these aphids could be maintained on a single plant for 16 weeks. These aphids retained their original characteristics, readily accepting radish, lettuce, and snapdragon as hosts, but accepted chrysanthemum only with great reluctance. Aphids from colonies that were maintained on roquette for 4 years did not lose their ability to transmit viruses.     

Effect of time of inoculation with potato leafroll virus on development of net necrosis and stem-end browning in potato tubers

The Green Mountain cultivar was used in field tests to determine the effects of inoculating potato plants at various times with the potato leafroll virus (PLRV) on development of internal necrosis of tuber tissue. Viruliferous apterae of the green peach aphid,Myzus persicae (Sulz.), were placed on each stem in all hills to be inoculated in each 3.0 m single-row plot. Planting and inoculation dates were varied in all field experiments and, in one, several vine-killing dates were also included. All harvested tubers were stored for approximately four months at 10°C to enhance development of internal necrosis prior to examination. Similar but smaller greenhouse studies involving both apterous and alate green peach aphids were also conducted using Green Mountain, Irish Cobbler, and Russet Burbank cultivars. All results showed that as inoculation was delayed relative to plant development, more net necrosis (NN) occurred. Conversely, when plants were inoculated early, stem-end browning (SEB) rather than NN predominated. A high percentage of naturally occurring SEB tubers (cv. Russet Burbank) were found by ELISA to contain PLRV. Plants produced by these tubers only rarely developed leafroll symptoms. These findings suggest a previously unsuspected causal relationship between SEB and PLRV. Implications of this apparent relationship on the epidemiology of potato leafroll in Maine are discussed.     

Epidemiology of potato leaf roll virus in the Fraser River delta of British Columbia

The spread of potato leaf roll virus (PLRV) and the resulting phloem necrosis in the tubers has been a limiting factor in the production of the Netted Gem (Russet Burbank) variety in southwestern British Columbia, Canada. Steckling sugar beets are an important overwintering host for nymphs and adults of the green peach aphid,Myzus persicae (Sulzer). By June, aphids are widely disseminated to the florets and new leaves of sugar beet and other hosts, including potato. Colonies with alates are produced on summer hosts which are not treated with insecticides. The peak of the flight of alates from the colonies on the summer hosts occurs during the first half of August. Those alates that were produced on PLRV-infected potato and which travel to other potatoes transmit the virus as soon as they feed. By the end of August, the sugar beet seed crops and the early and mid-season potato crops have been defoliated or harvested. Thus many colonies ofM. persicae are destroyed and the threat of PLRV spread diminishes. Crop and weed plants which serve as overwintering hosts become infested during late summer with alate aphids. Their offspring survive the winter in numbers which are determined by the weather and survival of host plants.     

Insecticidal control of cereal aphids and its impact on the epidemiology of the barley yellow dwarf luteoviruses

Imidacloprid is a seed-applied nitroguanidine insecticide that has both contact and long-lasting systemic properties. Its direct effects on cereal aphid populations and indirect effects on barley yellow dwarf luteovirus (BYDV) incidence were examined in laboratory and field studies. Adult longevity and fecundity of three aphid species caged on various aged, imidacloprid-treated oat or wheat plants was reduced, although the quantitative efficacy of the compound differed among aphid species. The transmission efficiency of BYDV by aphids to imidacloprid-treated plants was lower, relative to nontreated plants, when plants were 10 days old, but similar to nontreated when plants were 24 days old. In three years of field trials using winter wheat and two years using spring oat, aphid populations were reduced significantly in imidacloprid-treated plots relative to nontreated plots. Although the number of alighting alate aphids did not differ significantly between imidacloprid-treated or nontreated plots, the number of apterous aphids remained significantly lower in the treated plots for the majority of the growing season. BYDV epidemics did not develop in spring oat in either of the two years. BYDV epidemics did develop in the fall in the emerging winter wheat crop. Rhopalosiphum maidis was the predominant aphid migrating into the 1991–1992 crop. The incidence of the BYDV-RMV serotype was three times higher in nontreated plots than in imidacloprid-treated plots. In the 1992–1993 and 1994–1995 seasons, R. maidis and R. padi were the predominant aphids migrating into the crop, although R. padi was the predominant colonizing aphid. The incidence of BYDV-RMV was similar in imidacloprid treated and nontreated plots in 1992–1993, but the incidence of the BYDV-PAV serotype was significantly less in the treated plots. In 1994–1995, the incidence of both BYDV-PAV and BYDV-RMV was higher in the nontreated plots than in the imidacloprid-treated plots. Imidacloprid offers several advantages both in terms of its long-lasting systemic activity and its mode of applicaiton. As a seed treatment, the amount of material applied is minimized, there is little waste and the environmental impacts are reduced. The effectiveness of the compound at reducing the fecundity or reproductive rate of several aphid species may be advantageous in controlling secondary spread of viruses. However, the contact properties of the compound, important in repelling aphids or preventing phloem feeding, may be short-lived, thus reducing its effectiveness in preventing primary spread of the virus into the crop, especially under high aphid and inoculum pressure.     

Growth characteristics of potato plants useful in studies of population dynamics and biological control of aphids

During three growing seasons, certain information was recorded weekly that was related to several characteristics of the aerial growth of five varieties of field-growing potatoes, viz. the number of stems and leaves per plant, the length of stems, and leaf area. Conversions of aphid numbers recorded from stratified subsamples of plants in the field to the number of aphids per plant or per unit of leaf area became possible by knowing the number of leaves and the leaf area per plant at the time of each aphid count. The numbers and areas of leaves per plant varied greatly among varieties as well as within and among years. The range in average maximum area of leaves per plant was 533 to 2,523 in.² for the years 1967 to 1969. The comparable range for number of leaves per plant for the years 1967 and 1969 was 53 to 145. Consideration was given to the probable influence upon the magnitude of errors of estimate of aphid abundance that might result in making conversions of field counts of aphids to the numbers of aphids per plant or per unit of leaf area.     

Potato fungicides interfere with entomopathogenic fungi impacting population dynamics of green peach aphid

Fungicides applied to potato can enhance green peach aphid,Myzus persicae (Sulzer), outbreaks by interference with entomopathogenic fungi. (Order Entomophthorales). Late season aphid numbers were highest in potatoes sprayed with metalaxyl + mancozeb, captafol, or mancozeb, and lowest in potatoes sprayed with benomyl, triphenyltin hydroxide, chlorothalonil, or copper hydroxide. In field-collected aphids,Pandora (= Ernyia) neoaphidis (Remaudière et Hennebert) andEntomophthora planchoniana Cornu (F. Entomophthtoraceae) were the predominant cause of mycoses, 66.7% and 22.3%, respectively.Conidiobolus obscurus (Hall and Dunn) Remaudièe and Keller (F. Ancylistaceae) accounted for 8.5% of mycoses. In the laboratory, fungicides were shown to have direct effects on these entomopathogens. Metalaxyl + mancozeb, mancozeb and captafol were strongly inhibitory of germination of conidia, copper hydroxide was intermediate, and chlorothalonil had little effect. Triphenyltin hydroxide, benomyl, metalaxyl + mancozeb, and mancozeb were strongly inhibitory of growth of mycelia, copper hydroxide was intermediate, and chlorothalonil and copper hydroxide had least effect. Benomyl was highly toxic to green peach aphid, copper hydroxide and chlorothalonil intermediate, and captafol, mancozeb, and metalaxyl + mancozeb least toxic. Possible interference of potato fungicides with aphid pathogens is now an important consideration because of the intensity of spraying required to protect the crop from infection by metalaxyl-resistant strains of the late blight pathogen,Phytophthora infestans (Mont.) de Bary. Minnesota potato growers reported high green peach pressure in both 1995 and 1996, years of intensive fungicide spraying. Concomitantly, there was a marked increased in the incidence of PLRV in seed lots entered for winter testing.     

The spread of PVYo in New Brunswick potato fields: Timing and vectors

Field tests at three sites over a period of three to four years have shown that PVY^o spread in New Brunswick starts in mid-to late July when plants reach maximum height. Some 62 different genera or species of aphids were collected in experimental plots. Only seven of these were known vector species. Of the colonizing species, the alate green peach aphid,Myzus persicae (Sulzer), seems to be the most important vector. However, because it is not always present when disease spread starts, non-colonizing aphids are probably responsible for the early spread of PVY^o. Five of these species of aphids were tested in the laboratory to determine their vector efficiency. A list of potential vectors is presented. The impact of these findings on the management of PVY^o is discussed.     

大豆花叶病毒（SMV）主要介体及其传毒效率研究

大豆田大豆植株上繁殖危害的蚜虫,除大豆蚜、茄无网蚜外,豆蚜亦能暂居并少量繁殖危害。大豆田迁飞蚜虫种的数量,年度间和不同生境有所差异,但主要种基本一致。绿色诱盘捕获的迁飞蚜虫鉴定表明,主要迁飞蚜虫种,除以上三种,还有棉蚜、玉米蚜、禾缢蚜、桃蚜等,但大豆蚜占绝对优势。大豆植株上的翅蚜量,与绿色诱盘捕获的株冠面积着落翅蚜量,充分吻合。翅蚜迁飞频率与SMV流行速率相关密切。介体蚜虫传染SMV 83—02,得毒30—60秒的传毒效率高,以40—50秒的传毒率最高。供试得毒蚜虫,只桃蚜以2.94％的概率传毒至第二株其余均一株。最适得毒时间的传毒效率豆蚜最高58.33％、桃蚜47.66％,大豆蚜33.33％、茄无网蚜23.73％、玉米蚜12.90％、棉蚜最低4.29％。SMV主要介体为大豆蚜、豆蚜、桃蚜和茄无网蚜传染SMV亦有一定作用。