A differential interaction study of Bemisia tabaci Q-biotype on commercial tomato varieties with or without the Mi resistance gene, and comparative host responses with the B-biotype

Three tomato varieties (Motelle, Ronita, and VFN8) bearing the Mi-1.2 gene providing resistance to nematodes Meloidogyne spp. and to the potato aphid Macrosiphum euphorbiae Thomas, and three varieties not bearing this gene (Moneymaker, Roma, and Río Fuego), were compared by choice assay for host preference using the Q-biotype of Bemisia tabaci (Gennadius). The most preferred hosts, determined by infestation levels and numbers of feeding adults were Moneymaker, Río Fuego and Roma, all of which were not carrying the Mi gene. Ronita and Motelle, both of which bore the Mi gene, were the least preferred hosts. In a no-choice assay, B. tabaci females laid a significantly lower number of eggs on the varieties that carried the Mi gene than on those lacking the gene. Differences were more dramatic when plants carrying the Mi gene were pooled together and compared with pooled plants without this gene. Significantly greater values were obtained for the Mi-lacking group for all parameters tested. Comparing these results with those from a previous study on the B-biotype of B. tabaci, Q-biotypes were found to produce higher daily infestation rates on most of the tomato varieties. When results from plants carrying Mi were pooled, they showed lower infestation levels of Q-biotypes than B-biotypes. The Q-biotype infested less Mi-plants and more non-Mi plants than B-biotype. Q-biotype females produced significantly less pupae than the B-biotype females on both groups of plants. These results suggest the existence of an antixenosis and antibiosis-based resistance to the Q-biotype of B. tabaci in Mi-bearing commercial tomato varieties, which is greater than that previously reported for the B-biotype.     

Essential oils of catmint (<Emphasis Type="Italic">Nepeta meyeri</Emphasis> Benth.) induce oxidative stress in early seedlings of various weed species

The essential oils from the aerial parts of catmint (Nepeta meyeri Benth.) were analyzed by hydrodistillation with GC–MS. Fourteen compounds were identified in the yellowish essential oil of the plant, representing more than 99.07% of the oil, of which the major components were found to be 4aα,7α,7aβ-nepetalactone (83.4%) and 4aα,7α,7aα-nepetalactone (8.83%). The oils were characterized by relatively high content of oxygenated monoterpenes, and were tested on the germination and antioxidative systems in early seedlings of seven weed species (Amaranthus retroflexus L., Bromus danthoniae Trin., Bromus intermedius Guss., Chenopodium album L., Cynodon dactylon L., Lactuca serriola L., and Portulaca oleracea L.) and autotoxicity. The essential oil of N. meyeri inhibited seed germination by more than 50% in three weed species (B. danthoniae, B. intermedius, and L. serriola) when applied at a concentration of 0.01%. When the same oils were applied at 0.02% concentration, the inhibition of germination was more than 70% in two weeds (C. album and C. dactylon) and was 100% in four weeds (A. retroflexus, B. danthoniae, B. intermedius, and L. serriola). The essential oils increased CAT activity in all the weed species and decreased SOD activity, except in A. retroflexus. POX activity did not exhibit a revealing situation in the weed species tested. The essential oils increased the level of lipid peroxidation and hydrogen peroxide (H₂O₂) concentration in all the weeds studied. Our results show that the essential oils of N. meyeri have an important phytotoxic effect on seed germination and, consequently, seedling growth by exhausting antioxidative system of the weeds. The phytotoxic activity of the essential oils may be attributed to their relatively high content of oxygenated monoterpenes, especially 4aα,7α,7aβ-nepetalactone. It can be suggest that the essential oils of N. meyeri have the potential to be used as a bioherbicide.     

Somatic hybridization of an atrazine resistant biotype of Solanum nigrum with Solanum tuberosum

Summary Representative regenerated clonal plants from protoplast fusion of Solanum tuberosum L. and an atrazine resistant biotype of S. nigrum L. were studied to ascertain which plastomes each clone contained. DNA was isolated from fractionated chloroplasts, restricted with DNAases XHO-1, BGL-1, PVU-2 and BAM-H1, and the fragments separated by agarose gel electrophoresis for comparison. No difference could be found between resistant and susceptible biotypes of S. nigrum with all four enzymes. XHO-1, BGL-1, BAM-H1 differentiated between S. nigrum and S. tuberosum. All atrazine resistant regenerants, despite plant morphology, had the plastid DNA pattern of S. nigrum while all sensitive ones resembled S. tuberosum, even the subclone 38S having a S. nigrum morphology and chromosome number.     

Role of temperature in the germination ecology of three summer annual weeds

Summary Ambrosia artemisiifolia L., Chenopodium album L., and Amaranthus retroflexus L. are three summer annual weeds that occur in disturbed habitats. In nature, the peak germination season for A. artemisiifolia and C. album is in early to mid-spring, while in A. retroflexus the peak germination season is late spring to early summer. Furthermore, seeds of A. artemisiifolia germinate only in spring, while seeds of C. album and A. retroflexus germinate throughout the summer. In an attempt to explain the differential germination behavior of these three species in nature, changes in their germination responses to temperature during burial in a non-heated greenhouse from October 1974 to October 1975 were monitored. A high percentage of the seeds of all three species after-ripened during winter. Seeds of A. artemisiifolia and C. album germinated at temperatures characteristic of those in the field in early and mid-spring, but seeds of A. retroflexus required the higher temperatures of late spring and early summer for germination. Seeds of all three species germinated to higher percentages in light than in darkness. Non-dormant seeds of A. artemisiifolia that did not germinate in spring entered secondary dormancy. On the other hand, seeds of C. album and A. retroflexus that did not germinate when temperatures first became favorable for germination, did not enter secondary dormancy and, thus, retained the ability to germinate at summer field temperatures during summer. Thus, temporal differences in the germination behavior of these three species are caused by the differential reaction of the seeds to temperature during the annual temperature cycle.     

Weed species in tomato production and their role as alternate hosts of Tomato spotted wilt virus and its vector Frankliniella occidentalis

Tomato spotted wilt virus (TSWV) is an important plant virus that infects a wide range of hosts including weeds making its management difficult. A survey was undertaken to establish the occurrence of weed species in tomato production systems in Kenya and their role as hosts of TSWV and its vectors. Selected weed species were further evaluated for their reaction to TSWV, transmission efficiency by Frankliniella occidentalis and ability to support thrips reproduction. Of the 43 weed species identified in the field, 29 species had been reported as hosts of TSWV, two were non‐hosts and 11 had no record of their status. Among the more common species, Amaranthus hybridus, Solanum nigrum, Tagetes minuta and Datura stramonium were susceptible to the virus and supported high levels of thrips reproduction. The TSWV could not be transmitted to Galinsoga parviflora and Sonchus oleraceus by F. occidentalis despite them being highly susceptible in mechanical transmission tests. There was a significant correlation between feeding damage and number of larvae of F. occidentalis on different weeds. Occurrence of weeds that support thrips reproduction and are good hosts of TSWV is a clear indicator of their role in epidemiology and the importance of their management for disease control.     

Conserved structure of the chloroplast-DNA encoded D1 protein is essential for effective photoprotection via non-photochemical thermal dissipation in higher plants

Naturally selected atrazine-resistant (AR) weeds possessing a Ser₂₆₄ → Gly D1 protein encoded by a mutant psbA allele in the chloroplast-DNA have increased photosensitivity and lower fitness. The D1 mutant lines of S. nigrum revealed impaired regulation of photosystem II (PSII) activity as compared with the wild-type plants resulting in a less effective photochemical light utilization and in addition, a lower capacity of non-photochemical thermal dissipation (NPQ), one of the main photoprotective mechanisms in oxygenic photosynthetic organisms. In this work, comparative chlorophyll fluorescence analysis in attached leaves of wild-type and AR Solanum nigrum L. and in their reciprocal crosses has been used to establish how the lower NPQ is inherited. Both a 50% reduction in steady-state NPQ and a 60–70% reduction in the rapidly reversible, energy-dependent (qE) component of NPQ were common phenomena in the parent and hybrid lines of D1 mutant S. nigrum. The nuclear hybrid status of the F2 plant material was confirmed by morphological observations on fully developed leaves. No alteration was found in the nucleotide sequence and the deduced amino acid sequences of the nuclear psbS gene isolated from different biotypes of S. nigrum, and there were no differences in the expressions of both the PsbS and the D1 proteins. All things considered, co-inheritance of the lower photoprotective NPQ capacity and the Ser₂₆₄ → Gly D1 protein mutation was clearly observed, suggesting that the evolutionarily conserved D1 structure must be indispensable for the efficient NPQ process in higher plants.     

Potential allelopathic effect of neo-clerodane diterpenes from Teucrium chamaedrys (L.) on stenomediterranean and weed cosmopolitan species

The allelopathic effects of neo-clerodane diterpenes, isolated from Teucrium chamaedrys (L.), have been evaluated on the seed germination and seedling growth of four coexisting Mediterranean species (Dactylis hispanica, Petrorhagia velutina, Phleum subulatum and Petrorhagia saxifraga) and two cosmopolitan weeds (Amaranthus retroflexus and Avena fatua). All of the structures have been elucidated on the basis of their spectroscopic features. The bioassays data, analyzed by principal component analysis, showed more negative effects on weeds respect to coexisting species. Moreover D. hispanica, P. velutina, P. subulatum showed both stimulating or inhibiting effects depending on the type of metabolite and the concentration used in the test.     

红薯叶片浸提液对5种主要农田杂草种子萌发及幼苗生长的化感作用

以发芽率、发芽势、根长、茎长和鲜重变化为种子萌发和幼苗生长参数,研究了作物红薯叶片水浸液对云南省农田5种恶性杂草牛膝菊、藿香蓟、鬼针草、马唐和稗草的化感作用。结果表明,红薯叶片水浸液对5种受体杂草种子发芽率的影响不明显,但对发芽势有显著抑制作用。牛膝菊、藿香蓟、鬼针草和马唐的根长和生物量随红薯叶片水浸液浓度增加而显著降低,其中对马唐的抑制最强,高浓度0.1 g/m L时对根长和生物量抑制率分别为92.04%和73.33%,而低浓度0.0125 g/m L时分别为40.99%和46.67%;其次为鬼针草、藿香蓟、牛膝菊;最差的是稗草,随浓度的变化趋势均不明显。随红薯叶片水浸液浓度增加牛膝菊、鬼针草和马唐的茎长显著地降低,其中对马唐的抑制最强,高浓度0.1 g/m L和低浓度0.0125 g/m L时分别为86.85%和70.64%;其次为鬼针草和牛膝菊;相反藿香蓟和稗草的茎长随浓度增加而显著增加,高浓度0.1 g/m L和低浓度0.0125 g/m L时对藿香蓟的促进率分别为86.97%和16.03%。红薯叶片水浸液低浓度0.0125 g/m L时对牛膝菊的茎长和生物量有促进作用(低促高抑)。从化感作用响应指数和综合效应指数的综合对比来看,红薯对牛膝菊、藿香蓟、鬼针草、马唐具有显著的化感抑制作用,随浓度增加其抑制能力显著增加;其中对马唐的为最强,其次为鬼针草、牛膝菊和藿香蓟,相反对稗草具有促进作用(除了浓度0.1 g/m L)。所有这些表明,红薯叶片水浸液对5种杂草化感作用的敏感性趋势总体为:马唐鬼针草牛膝菊藿香蓟,最不敏感或者具有促进作用的是稗草。     

Parasitism ofLygus lineolaris eggs onCoronilla varia,solanum tuberosum,and three host weeds in southeastern Québec

Parasitism ofLygus lineolaris (Palisot de Beauvois) eggs by three species ofMymaridae, Anaphes iole Girault,Erythmelus miridiphagus Dozier andPolynema pratensiphagum Walley and one species ofScelionidae, Telenomus sp., was investigated at Ste-Anne-de-Bellevue, Québec. The maximum level of field parasitism ofL. lineolaris eggs by individual species was 15.4, 53.8, 70.0 and 16,7%, respectively. Parasitoids were retrieved from eggs ofL. lineolaris inserted in stems and branches ofAmaranthus retroflexus L.,Chenopodium album L.,Coronilla varia L.,Rumex obtusifolius L. andSolanum tuberosum L. Amaranthus retroflexus andS. tuberosum sustained a large population ofL. lineolaris and egg parasitism was high enough to consider it as a potential control factor.      

Suitability of common weed species as host plants for the potato leafhopper,Empoasca fabae

The suitability of 13 weed species as host plants for the potato leafhopper,Empoasca fabae (Harris) (Homoptera: Cicadellidae) was compared to alfalfa,Medicago sativa L., and broad bean,Vicia faba L., in laboratory and greenhouse tests. Nymphs developed and adults reproduced on five of the weeds: smartweed (Polygonum pensylvanicum L.), pigweed (Amaranthus retroflexus L.), shepherdspurse (Capsella bursa-pastoris (L.) Medic.), dandelion (Taraxacum officinale Weber), and carpetweed (Mollugo verticillata L.). Adults survived and oviposited on all tested weeds, suggesting that nymph survival was the limiting factor in host suitability. Yellow nutsedge (Cyperus esculentus L.), crabgrass (Digitaria sanguinalis (L.) Scop.), and foxtail (Setaria faberi Herrm.) were least suitable for adult and nymph survival. Large nymphs (instar III–IV) were able to complete development on weed species that did not support small nymph (instar I–II) development to adulthood. Densities of nymphs on weeds from alfalfa fields as well as the laboratory studies suggested that the weed species are less suitable as hosts and thus weeds probably do not affect population increases of potato leafhopper within weedy alfalfa fields by serving as hosts. Weeds may however, interact with the crop to alter leafhopper colonization, dispersal, and/or reproduction. In addition, since some broadleaf weeds are suitable hosts, the leafhopper may have a secondary beneficial role for biological weed control. These interactions should be considered when evaluating pest management practices.

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Eignung häufiger Unkrautarten als Wirte vonEmpoasca fabae

Zusammenfassung Der Wirtskreis derEmpoasca fabae (Harris) (Homoptera: Cicadellidae) wurde im Labor und im Freiland untersucht. Dreizehn Unkrautarten, wie auch Luzerne (Medicago sativa L.) undVicia faba L., wurden im Laborversuchen geprüft. Die Entwicklung der Nymphen und die Eiablage setzten auf fünf Unkrautarten fort: aufPolygonum pensylvanicum L.,Amaranthus retroflexus L.,Capsella bursa-pastoris (L.) Medic.,Taraxacum officinale Weber undMollugo verticillata L. Die Eiablage und das Weiterleben der Imagines geht auf allen untersuchten Unkräutern weiter. Dies weist darauf hin, dass die Lebensdauer der Nymphen die Eignung der Wirte begrenzt. Das Weiterleben der Imagines und der Nymphen waren aufCyperus esculentus L.,Digitaria sanguinalis (L.) Scop. undSetaria faberi Herrm. am stärksten verkürzt. Die Altnymphentwicklung (3. und 4. Stadien) bis zur Imago war auf Unkräutern gewährleistet, dagegen erfolgte die Jungnymphentwicklung (1. und 2. Stadien) bis zur Imago nicht. Populationsproben von Luzerne im Freiland, wie auch die Ergebnisse der Laboruntersuchungen, zeigten, dass Unkräuter nicht im Wirtskreis der Nymphen vonE. fabae sind und dass Unkräuter in Luzernefeldern keinen Einfluss auf die Populationszunahme in solcher Feldern haben. Unkräuter in Luzerne dürften aber die Kolonisierung, Verteilung der Population im Feld wie auch das Vermehrungspotential vonE. fabae verändern. Weil einige Unkräuter Wirte der Imago vonE. fabae sind, können sie als Ausweichpflanzen dienen, wenn die Luzerne, z.BB. nach dem Schnitt, für das Ueberleben der Zikaden ungeeignet ist.

     

Oversummering Hosts For Some Cucurbit Viruses in the Jordan Valley

Variable mosaic and yellow symptoms were often encountered in weeds growing during the summer of 1987 and 1988 in the Jordan Valley. Cucumber mosaic virus was recovered in the summer only from Dolicus lablab or from Solatium nigrum. In addition to the cucurbit weeds watermelon mosaic virus-2 occurred in Malva parviflora. Zucchini yellow mosaic virus was found in all tested cucurbit weeds except for Ecballium elaterium. Moreover this virus was isolated from Sysimbirium irio and Crepis aspera. Cucumber vein yellowing virus was recovered from some cucurbits with vein yellowing.     

微卫星位点BEM06与BEM23鉴别烟粉虱B型与Q型的有效性

烟粉虱Bemisia tabaci (Gennadius) B型与Q型是烟粉虱复合种中入侵性较强、分布较广的2种生物型, 当前在许多地区混合发生。这2种生物型的快速鉴别对其种群动态调查及入侵生态学研究具有重要价值。为了验证微卫星位点BEM06与BEM23鉴别B型与Q型烟粉虱的有效性, 本研究分析了这2个微卫星位点的等位基因在国内外17个B型、4个Q型、3个非B/Q型烟粉虱种群的分布特点。结果表明: 这2个微卫星位点的联合使用可鉴别B型与Q型烟粉虱, 但是无法有效地将B型、Q型与一些非B/Q型烟粉虱某些个体区分开来。结果提示: 利用微卫星位点BEM06与BEM23鉴别B型与Q型烟粉虱具有一定的局限性, 尤其是田间烟粉虱存在其他生物型时需要慎重使用这种鉴别方法。     

辽宁省冬季温室内越冬粉虱伪蛹的种类鉴定及烟粉虱体内番茄黄化曲叶病毒的检测

为了揭示辽宁省冬季温室内越冬粉虱伪蛹的种类及烟粉虱Bemisia tabaci （Gennadius）携带番茄黄化曲叶病毒（tomato yellow leaf curl virus, TYLCV）情况, 于2012年1月份在辽宁省不同县市区的温室作物上采集了17份粉虱伪蛹样品（每样品含30头粉虱伪蛹） , 镜检鉴别粉虱种类并利用mtCOI基因对烟粉虱生物型进行了鉴定; 检测了烟粉虱携带TYLCV情况并对其PCR扩增产物进行了测序分析。结 果表明： 辽宁省冬季温室内存在越冬温室白粉虱Trialeurodes vaporariorum （Westwood）与烟粉虱。17份粉虱样品中, 11份样品为烟 粉虱样品, 6份样品为温室白粉虱和烟粉虱混合样品。混合样品中, 温室白粉虱仅在锦州凌海（LH）样品中占优势。17份烟粉虱样品（包 括混合样品）中, 仅有4份样品为B型与Q型混合样品, 其他13份样品烟粉虱生物型均为Q型。17份烟粉虱样品中有3份Q型烟粉虱样品检测 到TYLCV, 系统树分析进一步证实该病毒是TYLCV。调查结果为辽宁省粉虱与TYLCV的早期测报和防控提供了科学依据。     

Attraction of the potential biocontrol agent Altica cyanea by volatile compounds of three species of Ludwigia weeds from rice fields

Ludwigia adscendens (L.) Hara, Ludwigia parviflora Roxb., and Ludwigia octovalvis (Jacq.) Raven (Onagraceae) are abundant weeds in rice fields in India. These weeds compete with rice for resources in fields and this results in reduction of grain yield. Altica cyanea (Weber) (Coleoptera: Chrysomelidae) is a biocontrol agent of the three rice-field weeds. Hence, it is relevant to study host preference of A. cyanea using volatile cues of these three weeds. Therefore, we attempted to identify volatiles from leaves of the three Ludwigia species attracting A. cyanea, which could be used as an attractant during early emergence of the weeds in rice fields. In Y-tube olfactometer assays, A. cyanea females were more attracted to natural volatiles of plants after 48 h of feeding by adults than to volatiles of undamaged plants. The volatile organic compounds from undamaged plants, and plants after 6 and 48 h of feeding by A. cyanea were identified and quantified by gas chromatography and mass spectrometry (GC–MS) and GC-flame ionization detection (FID), respectively. In total, 25, 29, and 29 volatile compounds were detected in headspaces of undamaged L. adscendens, L. parviflora, and L. octovalvis, respectively, whereas 32, 35, and 34 compounds, respectively, were detected after 48 h of feeding by A. cyanea. Methyl jasmonate predominated among the volatile compounds in all treatments, but this compound was not attractive to A. cyanea. Females were attracted by synthetic blends of 3-hexanol, α-pinene, linalool oxide, and phytol in amounts mimicking those in each of the three Ludwigia species after 48 h of feeding by A. cyanea. The blends mimicking L. adscendens and L. parviflora included geraniol, whereas the blend mimicking L. parviflora also included 1-tridecanol. These synthetic blends may be helpful to monitor A. cyanea in biocontrol programmes.     

贵州省烟田杂草优势种群的种间联结关系

在样方调查的基础上,采用方差比率法、Pearson点相关系数和X²检验分析贵州烟田杂草优势种群的种间关系。结果表明：①贵州省烟田杂草优势种的总体联结性为显著的正联结,处于比较稳定的状态;②Pearson点相关系数有21个种对呈正相关,23个种对呈负相关,尼泊尔蓼与繁缕无联结关系;③牛膝菊与马唐、尼泊尔蓼之间正联结关系达到极显著水平,牛膝菊与鸭趾草、马唐与尼泊尔蓼之间正联结关系为显著水平,其他种对之间均为不显著水平。本文旨在了解和掌握烟田杂草在群落中的分布状况,烟田杂草群落的演替趋势及为烟田杂草的防除提供基础资料。     

檀香与不同豆科植物寄生关系的研究

为了解檀香(Santalum album L.)与不同豆科植物的寄生关系,选取11种具有重要经济价值的豆科植物和檀香一起种植,对檀香叶片的光合特征和株高、地径以及寄主植物根系的吸器大小进行了测定。结果表明,檀香的吸器大小、数量在不同寄主之间存在很大差异,不同寄主对檀香的株高、地径也有显著差异。檀香的优良寄主有美洲合欢(Calliandra haematocephala)、苏木(Caesalpinia sappan)、台湾相思(Acacia confusa)、龙牙花(Erythrina corallodendron);一般的寄主植物有马占相思(Acacia mangium)、降香黄檀(Dalbergia odorifera)、黄槐(Cassia surattensis);不适宜的寄主植物有凤凰木(Delonix regia)、海南红豆(Ormosia pinnata)、银合欢(Leucaena leucocephala)、洋紫荆(Bauhinia blakeana)。同时,檀香的株高、地径及光合特征和吸器数量密切相关。因此,檀香种植时应选择适宜的优良寄主植物。     

穗醋栗MYB10基因克隆结构分析及功能验证

为探究花色苷合成相关转录因子MYB10在不同颜色穗醋栗果实着色差异的分子机理,通过cDNA末端快速扩增技术(rapid amplification of cDNA ends, RACE)法从果实花青素含量有较大差异的黑穗醋栗(Ribes nigrum L.)、红穗醋栗(Ribes rubrum L.)和白穗醋栗(Ribes album L.)中分别克隆出MYB10基因,分别命名为RnMYB10 (KY786107)、RrMYB10 (KY786108)和RaMYB10(MW660848)。系统发育分析表明,RnMYB10和RrMYB10在进化上具有同源性。实时荧光定量PCR(real-time quantitative PCR,RT-qPCR)结果表明:黑穗醋栗各时期果实中MYB10表达量均高于红穗醋栗且远远高于白穗醋栗。随着果实直径加大颜色加深,RnMYB10和RrMYB10表达量呈现先上升后下降的趋势(在果实转色程度75%时达到最大值),RaMYB10表达量极低,几乎无表达。过表达RnMYB10和RrMYB10的拟南芥呈现紫色叶柄和叶片,过表达RaMYB10的拟南芥无明显变化。说明...     

Preponderance of Oxygenated Sesquiterpenes and Diterpenes in the Volatile Oil Constituents of Lactuca serriola L. Revealed Antioxidant and Allelopathic Activity

Using synthetic chemicals in industry and agriculture has led to several environmental problems. Thus, plant products derived from volatile oils (VOs) could be a potential green source for bioherbicides. Little is known about the VOs of Lactuca serriola. Hence, the present study aimed to characterize the VOs chemical composition from the aerial parts of L. serriola, assessment of antioxidant activity, and evaluate allelopathic potential against the noxious weed Bidens pilosa. The VOs were extracted by hydrodistillation and analyzed by GC/MS. The VOs from the Egyptian ecospecies of L. serriola were found to comprise 34 compounds mainly oxygenated sesquiterpenes and diterpenes. The major compounds were isoshyobunone (64.22 %), isocembrol (17.35 %), and alloaromadendrene oxide‐1 (7.32 %). So, L. serriola can be considered as a good source for isoshyobunone, considering that it has a much higher concentration than any other plants. Also, this plant has a high content of the oxygenated diterpene compound, isocembrol, which is rarely found in the VOs of most plants. The VOs expressed strong antioxidant activity. Also, for the first time, our results showed a strong allelopathic activity of VOs from L. serriola on germination and seedling growth of the noxious weed, B. pilosa. We suppose that the activity of the VOs from L. serriola could be attributed to these previously mentioned major compounds, as they represent about 89 % of the total identified oil constituents. Nevertheless, to evaluate these compounds as new allelochemicals, further study is needed to test the allelopathic activity of authenticated standard of these compounds either singular or in combination on several weeds as well as evaluate the safety, and improve the efficacy and stability at the field scale.     

Performance of nymphal and adult Nezara viridula on selected alternate host plants

Laboratory studies with the southern green stink bug, Nezara viridula (L.) (Hemiptera: Pentatomidae), feeding on seeds or fruits of some alternate host plants, demonstrated differences in nymphal survival and development time, and body weight at adult emergence. Lowest mortalities (25%) were observed for nymphs on fruits of dakota mustard [Brassica kaber (DC.)] and siberian motherwort (Leonurus sibiricus L.). On fruits of castor bean (Ricinus communis L.) nymph mortality was ca. 60%, and on mature seeds of L. sibiricus ca. 75%. Total development time from second instar to adult ranged from ca. 26 days on B. kaber to ca. 42 days on R. communis. Fresh body weight at adult emergence was greatest for nymphs on L. sibiricus and lowest on R. communis. Adult survival after 30 days and mean longevity was greater on L. sibiricus than on the remaining foods, being drastically reduced on R. communis. In general, reproductive performance on all foods was similar, except R. communis, on which no female reproduced. Female weight gain of N. viridula was generally greater on L. sibiricus On R. communis, adults lost weight during their first week and showed the lowest weight gain at the end of day 29. Field observations coupled with these laboratory studies suggest that in the Warta area (northern Paraná state, Brazil, 23° 11 S), L. sibiricus and B. kaber are important alternate food plants in the seasonal phenology of N. viridula. R. communis, however, is of poor nutritional quality, serving primarily as a refuge.

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Résumé L'alimentation au laboratoire de N. viridula avec les graines et les fruits de diverses plantes a entraîné différentes mortalités larvaires, différentes vitesses de développement et des différences dans les poids des adultes à l'émergence. Les mortalités les plus faibles (25%) on été observées avec les fruits de Brassica kaber DC. et de Leonurus sibiricus L.Avec les fruits de Ricinus communis L., la mortalité larvaire était de 60%; sur graines mûres de L. sibiricus, elle était de 75%. La durée du développement du second stade à l'adulte a varié de 26 jours sur B. kaber à 42 jours sur R. communis. Le poids frais des adultes à l'émergence était le plus élevé avec L. sibiricus et le plus faible avec de R. communis. La longévité des adultes au-delà de 30 jours était la plus élevée avec L. sibiricus, et était fortement réduite avec R. communis. Dans l'ensemble, la reproduction était de même importance avec les différents aliments, à l'exception de R. communis avec lequel les femelles ne se reproduisaient pas. Le gain de poids des femelles était généralement supérieur avec L. sibiricus; avec R. communis les adultes ont perdu du poids pendant la première semaine et ont présenté le plus faible gain à la fin du 29ème jour.Des observations dans la nature, associées à ces expériences de laboratoire, laissent supposer que dans la zone de Warta (au Nord de l'état de Paraná, 23° 11 S, au Bresil), L. sibiricus et B. kaber sont des plantes hôtes alternatives importantes dans la phénologie saisonnière de N. viridula. Cependant, R. communis, de faible valeur alimentaire, sert avant tout de refuge.

     

Biotype-specific expression of dsRNA in the sweetpotato whitefly

This study was conducted to evaluate the effect of two different biotypes of the sweetpotato whitefly,Bemisia tabaci (Gennadius), on the induction of squash silverleaf (SSL), and to determine if double-stranded RNA (dsRNA) occurs in geographically remote populations of the two biotypes. Recently collected B-biotype whiteflies from Florida, Arizona, Mississippi, and Texas (SPW-B) all contained a 7.0 kb dsRNA molecule. Kb dsRNA molecule. Laboratory colonies of A-biotype whiteflies that were originally collected in 1981 from cotton in Arizona and California did not contain the 7.0 Kb dsRNA. When the two biotypes were compared only the SPW-B induced rapid onset, grade 5, SSL. DsRNA similar to that found in adult SPW-B was concentrated in whitefly nymphs, but host plant leaf tissue did not contain any consistent dsRNA molecules. SPW-A only induced low-grade SSL and progeny of SPW-A that were fed on pumpkin plants displaying SSL did not acquire the ability to express dsRNA or induce SSL. Our data suggest that dsRNA is not directly involved in the induction of SSL and that SSL is a host-specific response, to a feeding injury induced by B-biotype whiteflies. The origin and source of the 7.0 Kb dsRNA molecule remains enigmatic but its expression is constant in the whitefly biotype that is responsible for the induction of SSL and several other plant disorders in the U.S.