Identification of phloem sieve elements as the site of resistance to silverleaf whitefly in resistant alfalfa genotypes

Experiments were conducted to locate the plant tissue where resistance is expressed against silverleaf whitefly, Bemisia argentifolii Bellows and Perring (Homoptera: Aleyrodidae), in alfalfa, Medicago sativa L. (Fabaceae), genotypes previously shown to have high levels of resistance against this pest. Previous work demonstrated that resistance in the resistant alfalfa genotypes was expressed primarily as high first‐instar mortality; consequently this study focused on first‐instar nymphs. Examination of stylets in cleared leaf tissue indicated that first‐instar nymphs located vascular bundles with equal success on resistant and susceptible alfalfa genotypes. Furthermore, direct current electrical penetration graphs (DC‐EPG) indicated that sieve elements were penetrated and phloem ingestion behavior was initiated with equal success on resistant and susceptible genotypes. Thus, the mechanism of resistance does not reside in tissues encountered by the stylets prior to penetrating a phloem sieve element. Honeydew production (as a proxy for ingestion) was greatly reduced on two resistant genotypes compared to the two susceptible genotypes. The frequency distribution of honeydew production was bimodal, indicating that most individuals on the resistant genotypes produced little or no honeydew while some produced as much honeydew as whiteflies on the susceptible genotypes. This indicates that expression of resistance is an all‐or‐nothing phenomenon; an individual nymph either encounters resistance and cannot sustain ingestion or it does not encounter resistance and ingests just as well as on a susceptible plant. Intermediates are rare. DC‐EPGs indicate that phloem ingestion behavior is significantly reduced on two of the resistant genotypes compared to the susceptible genotypes. The primary reason for this appears to be more frequent termination of phloem ingestion behavior on at least one of the resistant genotypes. On one of the resistant genotypes, the productivity of EPG‐measured phloem ingestion behavior (honeydew produced per min of phloem ingestion behavior) was reduced compared to a susceptible control.     

Probing behaviour of Cacopsylla pyri on a resistant pear selection

European pear psylla Cacopsylla pyri L. (Hemiptera Psyllidae) is one of the worst pests of pear (Pyrus communis L.) in Europe. We investigated probing behaviour in adults and nymphs of C. pyri by full EPG on a psylla‐resistant pear selection, NY 10353. Concerning stylet probing behaviour on the plant surface, the results showed no significant differences between the resistant selection and the susceptible cultivar Bartlett, and no differences were also detected for epidermis and mesophyll resistance in the same conditions. For mesophyll/phloem, no differences were found in adults. However, in nymphs, weak resistance factors (longer stylet penetration and mesophyll salivation) were detected in the resistant selection. In phloem, EPG data indicate strong resistance factors in NY 10353, especially for nymphs and summer‐form adults (longer time before the first phloem ingestion and a lower duration of each phloem ingestion event). No prolonged (>10 min) phloem ingestion was performed by nymphs and adults in the resistant selection. The results support the hypothesis that NY 10353 resistance factors are located in the phloem sap and cause high C. pyri nymph mortality: this could be useful as a basis for further investigations of resistance mechanisms at the metabolic, chemical and genetic levels.     

Characterization and correlation of DC electrical penetration graph waveforms with feeding behavior of beet leafhopper, Circulifer tenellus

Feeding behavior of beet leafhopper, Circulifer tenellus (Baker) (Homoptera: Cicadellidae), was studied with a DC electrical penetration graph. Nine different electrical penetration graph waveforms associated with feeding were identified and characterized. Waveforms were correlated with specific feeding behaviors using a number of techniques, including high magnification video recording, honeydew analysis, stylectomy, and histological processing. Waveforms were grouped into three phases based on feeding behavior: pathway phase (waveforms A, B1, B2, and C), non-phloem ingestion phase (waveform G), and phloem phase (waveforms D1, D2, D3, and D4). No ingestion was found to occur during waveforms A, B1, B2, and C. Waveform G was associated primarily with ingestion of xylem sap and occasionally with ingestion of mesophyll sap. Stylet tips were located in phloem during waveforms D1, D2, and D3, and waveforms D2 and D3 were correlated with ingestion of phloem sap. Waveform D4 probably also plays a role in phloem ingestion, because D4 is very brief and always occurs embedded in either waveform D2 or D3. In contrast to most other homopteran insects, rate of honeydew production (and hence rate of ingestion) was much lower on phloem than on xylem. More rapid rates of ingestion are expected on phloem, because its high turgor pressure drives sap into the feeding insect whereas the negative pressure of xylem sap is expected to cause a slow rate of ingestion. The very slow ingestion rate of beet leafhopper feeding on phloem suggests that it is not able to exploit the high turgor pressure of phloem to achieve the high rate of ingestion that is typical of phloem ingestion by other insects.     

Foraging ofRhagoletis pomonella flies in relation to interactive food and fruit resources

Feeding behaviour of the lettuce root aphidPemphigus bursarius was monitored electronically on six lettuce varieties. Aphids, monitored for a minimum of 5 h on lettuce roots, performed recognizable feeding behaviour on the susceptible varieties, Webbs Wonderful and Borough Wonder including non probing, pattern A start of new penetration, C (stylet pathway activities) sometimes including clear B-waves (salivary sheath secretions), potential drops (intracellular penetrations), intracellular E (phloem ingestion) distinguishing E₁ and E₂ (Tjallingii, 1990) and occasionally xylem ingestion. Although aphid probing was recorded on the resistant varieties Lakeland and Grand Rapids continued penetration to the phloem elements was deterred and the time spent ingesting phloem was short. Aphids rarely probed the resistant varieties Avoncrisp and Avondefiance and all attempted penetrations quickly terminated.     

Feeding behavior and performance of Nasonovia ribisnigri on grafts,detached leaves,and leaf disks of resistant and susceptible lettuce

Aphids are dependent on the phloem sap of plants as their only source of nutrients. Host‐plant resistance in lettuce, Lactuca sativa L. (Asteraceae), mediated by the Nr gene is used to control the lettuce aphid Nasonovia ribisnigri (Mosely) (Hemiptera: Aphididae). The resistance is located in the phloem; however, the exact mechanism of resistance is unknown. In this study, we investigated whether the resistance factor (or factors) is synthesized in the root or in the shoot. The feeding behavior and performance of avirulent N. ribisnigri were studied on grafts of resistant and susceptible lettuce. In addition, the persistence of resistance in excised lettuce tissue was measured, by studying the feeding behavior and performance of N. ribisnigri on detached leaves and leaf disks of resistant lettuce. It appears that the resistance factor encoded by the Nr gene is produced in the shoots: aphid feeding was reduced on resistant shoots grafted on susceptible roots, whereas aphids were able to feed on grafts of susceptible shoots on resistant roots. Partial loss of resistance was observed after detachment of leaves and excision of leaf disks from resistant plants. Aphids fed longer on excised resistant plant tissue compared with intact resistant plants; however, compared with excised plant tissue of the susceptible cultivar, the time spent on feeding was shorter, indicating resistance was not completely lost. Our findings caution against the use of excised leaf material for aphid resistance bioassays.     

Mi‐mediated aphid resistance in tomato: tissue localization and impact on the feeding behavior of two potato aphid clones with differing levels of virulence

The Mi‐1.2 gene in tomato, Solanum lycopersicum L. (Solanaceae), confers resistance against several herbivores, including the potato aphid, Macrosiphum euphorbiae (Thomas) (Hemiptera: Sternorrhyncha: Aphididae) and the sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Sternorrhyncha: Aleyrodidae). Previous studies on the tissue localization of resistance have given varying results; whitefly resistance was attributed to factors localized in the mesophyll or epidermis, whereas aphid resistance was attributed to factors localized in the phloem. Our study utilizes the direct current electrical penetration graph (DC‐EPG) technique to compare aphid feeding behavior on resistant (Mi‐1.2+) and susceptible (Mi‐1.2?) tomato plants. This study also compares the impact of resistance on the feeding behavior of two aphid clones that vary in their virulence, or their ability to survive and reproduce on resistant plants. Previous work had shown that the avirulent WU11 clone is almost completely inhibited by resistance, whereas the semi‐virulent WU12 clone can colonize resistant hosts. Here, DC‐EPG analysis shows that both aphid clones take longer to initiate cell sampling and to establish a confirmed sieve element phase on resistant plants than on susceptible hosts, and have shorter ingestion periods on resistant plants. However, the magnitude of these deterrent effects is far less for the semi‐virulent clone than for the avirulent aphids. In particular, the WU12 clone is less sensitive to factors that limit sieve element ingestion, showing shorter non‐probe duration and rapidly establishing sustained phloem ingestion on resistant plants when compared to the WU11 clone. We conclude that, in addition to previously described factors in the phloem that inhibit ingestion, Mi‐mediated aphid resistance also involves factors (possibly in the mesophyll and/or epidermis) that delay initiation of phloem salivation, and that act in the intercellular spaces to deter the first cell sampling. Furthermore, the relative effectiveness of these components of resistance differs among insect populations.     

Behavioral responses of the whitebacked planthopperSogatella furcifera (Homoptera: Delphacidae) on rice plants whose odors have been masked

In a two-choice test, moreS. furcifera females settled more often on exposed plants than on parafilm-masked ones, regardless of the susceptibility of rice varieties. This indicates that rice volatiles play an important role in the insect's short-range orientation to its host. The fact that more insects settled on exposed resistant Rathu Heenati (RHT) than to masked susceptible Taichung Native 1 (TN1) suggests that there must be certain common volatiles released by both varieties. Few females landed on masked plants of either RHT or TN1. This implies that the insect could not recognize at a distance that a plant was resistant or susceptible without olfactory stimuli.S. furcifera excreted less honeydew on masked plants than on exposed ones for both varieties and more on masked TN1 than on exposed RHT. The electronic monitoring of feeding behavior demonstrates that the insect made more frequent probes and had shorter phloem ingestion durations on exposed RHT than on exposed TN1 and on masked RHT than on masked TN1. Moreover, the insect had longer phloem ingestion durations on masked TN1 than on exposed RHT. These results suggest that volatile chemicals given off by resistant RHT plants have a negative effect on feeding.     

Probing behaviour of the green peach aphid Myzus persicae on resistant Prunus genotypes

Electrical penetration graphs of Myzus persicae (Sulzer) (Homoptera: Aphididae) feeding behaviour on four resistant and two susceptible genotypes of peach (Prunus persica L. Batsch) and related species showed that resistance was mainly linked to (i) reduced duration of phloem sap uptake, (ii) reduced percentage of pattern E1 (salivary secretion into sieve elements) followed by pattern E2 (sap ingestion) and (iii) increased number of shifts from E1 to E2 and back. These results suggest the unsuitability of phloem sap, and thus repetitive failures to initiate sustained ingestion. Extensive comparisons of the EPGs also revealed more specific trends. Aphids on the most susceptible cultivar GF305 produced significantly longer potential drops than on other peach genotypes. On the resistant Rubira, aphids generated more penetrations before the first E occurred, indicating the possible presence of a resistance factor before the phloem was reached. The clone P1908 of the wild species Prunus davidiana displayed traits of both susceptibility (less but longer probes) and resistance. In particular, aphids produced more E1, suggesting difficulties in preparing sieve elements before feeding. The aphid probing process could be correlated with aphid settling behaviour and bionomics, as previously reported, and gave evidence for the existence of different mechanisms underlying resistance in the tested genotypes against M. persicae.     

Location of the mechanism of resistance to Amphorophora agathonica (Hemiptera: Aphididae) in red raspberry

The aphid Amphorophora agathonica Hottes (Hemiptera: Aphididae) is an important virus vector in red (Rubus idaeus L.) and black (Rubus occidentalis L.) raspberries in North America. Raspberry resistance to A. agathonica in the form of a single dominant gene named Ag1 has been relied upon to help control aphid-transmitted plant viruses; however, the mechanism of resistance to the insect is poorly understood. Aphid feeding was monitored using an electrical penetration graph on the resistant red raspberry 'Tulameen' and compared with a susceptible control, 'Vintage'. There were no differences in pathway feeding behaviors of aphids as they moved toward the phloem. Once in the phloem, however, aphids feeding on resistant plants spent significantly more time salivating than on susceptible plants, and ingested significantly less phloem sap. This suggests that a mechanism for resistance to A. agathonica is located in the phloem. Reduced ingestion of phloem may result in inefficient acquisition of viruses and is a likely explanation for the lack of aphid-transmitted viruses in plantings of resistant cultivars.     

Analysis of resistance in tomato and sweet pepper against the greenhouse whitefly using electrically monitored and visually observed probing and feeding behaviour

Different types of plant resistance against the greenhouse whitefly, Trialeurodes vaporariorum, were distinguished according to the tissue location of the resistance factors. The effects of resistance factors were compared by measuring the electrically monitored and visually observed probing and feeding behaviour of whiteflies on two resistant tomato genotypes (82207 and 82216), a susceptible tomato cultivar, and a non-host plant, sweet pepper. On sweet pepper, whiteflies displayed very short first probes, very long pathway probing and spent much time on non-feeding activities such as walking and standing still. Also, a high percentage of whiteflies rejected sweet pepper without ingesting substances from the phloem vessel. These data suggest a strong resistance that is based on the factors present in surface/epidermis and/or mesophyll layers of this plant. The behaviour of whiteflies on tomato 82207 was very different from that on sweet pepper. On tomato 82207 whiteflies apparently did not perceive resistance factors on the leaf surface and in the mesophyll. Resistance factors appeared to be present in the phloem tissue, because a higher number of phloem phases, longer phloem salivation periods and shorter phloem ingestion periods were observed when compared with the susceptible tomato cultivar. Tomato 82216 showed no clear resistance factor in the phloem. The importance of combined EPG and behavioural research for host-plant resistance studies are discussed.     

Feeding by sugarcane aphid,Melanaphis sacchari,on sugarcane cultivars with differential susceptibility and potential mechanism of resistance

Feeding behavior of Melanaphis sacchari Zehntner (Hemiptera: Aphididae) was studied on sugarcane, Saccharum spp. (Poaceae), cultivars HoCP 91‐555 (resistant), LCP 85‐384 (moderately resistant), and L 97‐128 (susceptible) using the electrical penetration graph (EPG) technique. Constitutive concentrations of total phenolics and available carbohydrates, water potential at the whole‐leaf tissue level, and free amino acids (FAAs) in phloem sap extracts, and in honeydew produced by aphids fed on L 97‐128 and HoCP 91‐555 were determined. Cultivar did not influence time for M. sacchari to access phloem sieve elements. Total time in sieve elements was ca. two‐fold greater on L 97‐128 than on HoCP 91‐555, whereas it did not differ from LCP 85‐384 in either cultivar. The mean duration of individual events associated with phloem sap ingestion was ca. 50% shorter on both HoCP 91‐555 and LCP 85‐384 than on L 97‐128. Although cultivar effects were not detected for levels of total phenolics, available carbohydrates, and water potential, two free essential amino acids, histidine and arginine, were absent from phloem sap in HoCP 91‐555. Two free essential amino acids, leucine and isoleucine, and two free non‐essential amino acids, tyrosine and proline, were absent from honeydew of aphids fed on HoCP 91‐555. These results suggest that despite apparent biosynthesis of some FAAs, the absence of important FAAs in the phloem sap of HoCP 91‐555 and the inability of M. sacchari and its endosymbionts (e.g., Buchnera) to derive specific free essential and non‐essential amino acids from other ingested molecules, possibly along with other unidentified factors, underlie the pest's decreased phloem sap ingestion and consequently reduced growth potential on HoCP 91‐555.     

Triticum monococcum lines with distinct metabolic phenotypes and phloem‐based partial resistance to the bird cherry–oat aphid Rhopalosiphum padi

Crop protection is an integral part of establishing food security, by protecting the yield potential of crops. Cereal aphids cause yield losses by direct damage and transmission of viruses. Some wild relatives of wheat show resistance to aphids but the mechanisms remain unresolved. In order to elucidate the location of the partial resistance to the bird cherry–oat aphid, Rhopalosiphum padi, in diploid wheat lines of Triticum monococcum, we conducted aphid performance studies using developmental bioassays and electrical penetration graphs, as well as metabolic profiling of partially resistant and susceptible lines. This demonstrated that the partial resistance is related to a delayed effect on the reproduction and development of R. padi. The observed partial resistance is phloem based and is shown by an increase in number of probes before the first phloem ingestion, a higher number and duration of salivation events without subsequent phloem feeding and a shorter time spent phloem feeding on plants with reduced susceptibility. Clear metabolic phenotypes separate partially resistant and susceptible lines, with the former having lower levels of the majority of primary metabolites, including total carbohydrates. A number of compounds were identified as being at different levels in the susceptible and partially resistant lines, with asparagine, octopamine and glycine betaine elevated in less susceptible lines without aphid infestation. In addition, two of those, asparagine and octopamine, as well as threonine, glutamine, succinate, trehalose, glycerol, guanosine and choline increased in response to infestation, accumulating in plant tissue localised close to aphid feeding after 24 h. There was no clear evidence of systemic plant response to aphid infestation.     

不同水稻品种上白背飞虱取食行为的EPG分析

【目的】为探明不同水稻品种（丰源优272、R9810-T、华恢1号、明恢63、麻糯谷和Rathu Heenati）对白背飞虱Sogatella furcifera的抗性差异机理,利用刺吸电位技术(electronic penetration graph, EPG)记录了该虫在这6个品种三叶期稻苗上的取食行为。【方法】结合特定的EPG波形,考察了9个非韧皮部指标和22个韧皮部指标。【结果】在总记录时间8 h内,白背飞虱在品种Rathu Heenati上非刺探波np的总时间最长,其次是麻糯谷上非刺探波np的总时间,这两者间差异显著且都显著地长于其他4个品种的np总时间(P<0.05);该虫在Rathu Heenati上路径波Nc的总时间为8 523.41 s,是感虫品种明恢63 Nc总时间的2.24倍;该虫在Rathu Heenati上吸食韧皮部汁液N4-b的总时间显著地比其他品种短(P<0.05)。华恢1号和R9810-T上所有的EPG指标和感虫品种明恢63的EPG指标都没有显著的差异(P≥0.05)。白背飞虱在丰源优272上单次分泌水溶性唾液N4-a的平均时间更长,并伴随长时间的韧皮部取食。【结论】由此推测,品种Rathu Heenati可能存在不利于白背飞虱取食的忌避成分,并且在韧皮部外组织和韧皮部组织都存在抗性因子;在麻糯谷上仅存在忌避成分;然而,品种华恢1号和R9810-T可能对白背飞虱不具有明显的抗性;丰源优272可能是比明恢63更为感虫的品种。结合介体昆虫取食行为与传播持久性病毒的关系,这些结果也为利用抗白背飞虱品种控制南方水稻黑条矮缩病提供了参考。     

Feeding behavior of aphids on narrow‐leafed lupin (Lupinus angustifolius) genotypes varying in the content of quinolizidine alkaloids

Since the beginning of breeding narrow‐leafed lupins [Lupinus angustifolius L. (Fabaceae)] with a low alkaloid content, susceptibility to several aphid species has increased. Therefore, the probing and feeding behavior of Aphis fabae Scopoli, Aphis craccivora Koch, Acyrthosiphon pisum (Harris), Myzus persicae (Sulzer), and the well‐adapted Macrosiphum albifrons Essig (all Hemiptera: Aphididae) was studied over 12 h on narrow‐leafed lupin genotypes containing varying amounts and compositions of alkaloids. We used the electrical penetration graph (EPG) technique to obtain information on the influence of alkaloid content and composition on the susceptibility to various aphid species. Results indicated that the total time of probing of A. fabae, A. craccivora, A. pisum, and M. persicae increased with a reduced alkaloid content, whereas the alkaloid content had no influence on M. albifrons. Almost all of the individuals (>93%) conducted sieve element phases on the highly susceptible genotype Bo083521AR (low alkaloid content). A reduced occurrence of phloem phases was observed during the 12‐h recording on the alkaloid‐rich cultivar Azuro, especially for A. pisum (37.5%) and A. fabae (55.0%). Furthermore, aphids feeding on genotypes with low alkaloid content had in most cases significantly longer sieve element phases than when feeding on resistant genotypes (Kalya: low alkaloid content, yet resistant; Azuro: high alkaloid content, resistant), whereas M. albifrons showed the longest phloem phase on the alkaloid‐rich cultivar Azuro. As most significant differences were found in phloem‐related parameters, it is likely that the most important plant factors influencing aphid probing and feeding behavior are localized in the sieve elements. The aphids’ feeding behavior on the cultivar Kalya, with a low alkaloid content but reduced susceptibility, indicates that not only the total alkaloid content influences the feeding behavior but additional plant factors have an impact.     

Electronically monitored cowpea aphid feeding behavior on resistant and susceptible lupins

The feeding behavior of cowpea aphid, Aphis craccivora Koch (Homoptera: Aphididae) was examined on seedlings of narrow leafed lupin, Lupinus angustifolius L., and yellow lupin, L. luteus L., using electronic monitoring of insect feeding behavior (EMIF). Aphid feeding behavior was first compared between resistant (cv. Kalya) and susceptible (cv. Tallerack) varieties of narrow-leafed lupin. Aphids spent significantly more time in non- penetration and stylet pathway activities, and significantly less time in the sieve element phase on Kalya than on Tallerack, suggesting that feeding deterrence is an important component of aphid resistance in Kalya. Aphid feeding on a susceptible yellow lupin variety (cv. Wodjil) was then compared with that on two resistant lines, one (Teo) with high and the other (94D024-1) with low seed alkaloid content. There were no consistent differences in aphid feeding behavior between Wodjil and Teo. Total, mean and percentage sieve element phase times were significantly lower, and total and percentage times in non-phloem phase were greater on 94D024-1 than on Wodjil, suggesting the possibility of phloem-based deterrence in 94D024-1.     

Ultrastructure of compatible and incompatible interactions in phloem sieve elements during the stylet penetration by cotton aphids in melon

Resistance of the melon line TGR‐1551 to the aphid Aphis gossypii is based on preventing aphids from ingesting phloem sap. In electrical penetration graphs (EPGs), this resistance has been characterized with A. gossypii showing unusually long phloem salivation periods (waveform E1) mostly followed by pathway activities (waveform C) or if followed by phloem ingestion (waveform E2), ingestion was not sustained for more than 10 min. Stylectomy with aphids on susceptible and resistant plants was performed during EPG recording while the stylet tips were phloem inserted. This was followed by dissection of the penetrated leaf section, plant tissue fixation, resin embedding, and ultrathin sectioning for transmission electron microscopic observation in order to study the resistance mechanism in the TGR. The most obvious aspect appeared to be the coagulation of phloem proteins inside the stylet canals and the punctured sieve elements. Stylets of 5 aphids per genotype were amputated during sieve element (SE) salivation (E1) and SE ingestion (E2). Cross‐sections of stylet bundles in susceptible melon plants showed that the contents of the stylet canals were totally clear and also, no coagulated phloem proteins occurred in their punctured sieve elements. In contrast, electron‐dense coagulations were found in both locations in the resistant plants. Due to calcium binding, aphid saliva has been hypothesized to play an essential role in preventing/suppressing such coagulations that cause occlusion of sieves plate and in the food canal of the aphid's stylets. Doubts about this role of E1 salivation are discussed on the basis of our results.     

Analysis of wheat resistance to the cereal aphidSitobion avenae using electrical penetration graphs and flow charts combined with correspondence analysis

The behaviour ofSitobion avenae (F.), was compared on resistant wheat lines ofTriticum monococcum (L.) and a susceptible variety ofTriticum aestivum (L.). Firstly, stylet penetration activities were monitored with the Electrical Penetration Graph (EPG) technique and subsequently analysed using flow charts combined with correspondence analysis. Plant resistance was shown to be associated with repeated penetrations without access to either the xylem or the phloem, and with numerous failures in starting a sustained sap ingestion (as represented by pattern E2). Access to sieve elements of the phloem did not seem to be much affected on resistant plants but it took the aphid three times as long to produce a sap ingestion pattern when maintained on the resistant lineT. monococcum n^o 44 (Tm44) as compared with aphids maintained on susceptible plants. As a result the total time spent in ingesting from sieve elements was reduced by 72% on Tm44. Secondly, direct observations of freely-moving apterous adults were performed. Aphids did not discriminate between resistant and susceptible wheat during the first 30 min of access to test leaves, but only 4 out of 25 aphids were still probing after eight hours on resistant Tm44. The relevance of these results to possible location of the resistance factor(s) are discussed. Although detection of plant resistance before sieve elements are reached can not be rigorously excluded, the factors involved inT. monococcum resistance toS. avenae undoubtedly occur within the phloem vessels.     

电子取食监测仪在植物抗虫性研究中的应用

主要综述了电子取食监测仪在植物对同翅目昆虫抗虫性研究中的应用情况.利用电子取食监测仪可监测同翅目昆虫（蚜虫、飞虱、叶蝉、蓟马、粉虱等）在不同抗、感虫品种上的取食行为,并根据取食行为参数如刺探频率、唾液分泌时间、韧皮部取食时间等在不同抗、感品种上的差异来区别品种的抗、感虫特性和确定抗虫因子存在的部位.     

Induced resistance by Myzus persicae in the peach cultivar `Rubira'

The effect of a previous infestation by the green peach aphid Myzus persicae (Sulzer) on the settling behaviour and reproduction of the same aphid species was investigated in the resistant peach cultivar Rubira, and compared with that observed in the susceptible control cultivar GF305. A previous infestation of 48 h triggered induced resistance in Rubira. There were significantly fewer aphids settling on preinfested than on uninfested plants, indicating an increased rejection of Rubira as a host plant. The level of induced resistance in preinfested plants was positively related to the duration of the first infestation. In GF305, previous infestation had no detrimental effect on aphid settlement and even slightly enhanced larviposition by adult females. The aphid probing behaviour after a 48-h preinfestation was also monitored for 8 h with the electrical peneration graph (EPG) technique. On preinfested GF305, most EPG parameters indicated an enhanced host plant acceptance. On preinfested GF305, aphids produced less sieve element salivation and more continuous sap ingestion than on uninfested GF305, indicating that the previous aphids provoked changes in plant properties beneficial to the test aphids. In Rubira, a major induced factor of resistance was thought to be expressed in the sieve element as phloem sap ingestion was 4-fold shorter on preinfested than on uninfested plants. The time taken by the aphid stylets to reach a sieve element was also significantly increased on preinfested Rubira, suggesting the induction of resistance factors outside the phloem. The originality of the Rubira/M. persicae interaction is discussed in the perspective of a better understanding of plant induced responses to aphids.     

Russian wheat aphid biotype RWASA2 causes more vascular disruption than RWASA1 on resistant barley lines

We investigated the comparative effects of the feeding damage caused by two Russian wheat aphid (RWA, Diuraphis noxia Kurdjumov) biotypes, RWASA1 and RWASA2, on leaves of three RWA-resistant barley (Hordeum vulgare L.) lines from the USDA-ARS, and used a South African non-resistant cultivar as control. The relationship between aphid breeding capacity and the structural damage inflicted by the aphids was studied, using wide-field fluorescence and transmission electron microscopy (TEM). Colonies of the two biotypes grew rapidly on all four barley lines during a 10 day feeding exposure but as expected, population size and density were generally lower on the resistant lines than on the non-resistant cultivar. The new South African biotype, RWASA2, bred significantly faster than the original RWASA1 biotype. The feeding and water uptake-related damage sustained by phloem and xylem tissues of the resistant lines suggest that RWASA2 was a more aggressive feeder and caused substantially more cell damage than RWASA1. Examination of wound callose distribution after aphid feeding revealed that high levels of wound callose occurred in non-resistant and in resistant lines. Reduction in aphid population size, as well as ultrastructural damage during feeding by RWA biotypes on resistant lines, signals potential antibiotic and tolerant responses of the barley lines to aphid feeding. We infer from callose distribution and ultrastructural studies, that phloem transport would be substantially reduced in the non-resistant PUMA and to a lesser extent in the resistant STARS lines, which suggests that the STARS lines may be a potential source of RWASA1 and RWASA2-resistance.