An analysis of the feeding behavior of three stages of Toxoptera citricida by DC electrical penetration graph waveforms

With the purpose of studying the feeding behavior of the brown citrus aphid pest, Toxoptera citricida (Kirkaldy) (Hemiptera: Aphididae), we compared stylet probing behaviors of third and fourth instars and adults on Citrus unshiu Marc (Rutaceae) seedlings using the electrical penetration graph (EPG) technique. EPG waveforms exhibited the full suite of stylet behaviors – stylet pathway, intracellular stylet puncture, phloem salivation (E1), sieve ingestion (E2), and xylem sap ingestion activities, plus the non‐penetration (Np) waveform. Before the phloem phase, the number of probes was significantly higher for third‐instar nymphs than for adults. Overall duration of Np events by adults was significantly lower than the duration of third and fourth instars. The number of short probes of the fourth instars was significantly higher than that of the adults. In the phloem phase, adults made more frequent and longer E1 events than the third and fourth instars. Third instars made more frequent but shorter E2 events, whereas adults made fewer but longer events. These results showed adults gained nutrients by increasing feeding time during phloem ingestion. Thus, the probability of phloem‐associated virus acquisition and transmission of T. citricida was higher in adults than in nymphs.     

Characterization of the feeding behavior of three Erythroneura species on grapevine by histological and DC‐electrical penetration graph techniques

Feeding behavior of three leafhopper species – Erythroneura vitis (Harris), Erythroneura ziczac (Walsh), and Erythroneura elegantula (Say) (Hemiptera: Cicadellidae) – reared on grapevine, Vitis vinifera L. cv. ‘Seyval blanc’ (Vitaceae), was investigated using histological techniques and DC‐electrical penetration graphs (DC‐EPG). Histological studies revealed that the Erythroneura species induced white stipples on the leaves and that these leafhoppers produced thin salivary sheaths in grapevine leaf tissues. The DC‐EPG system allowed the characterization of five waveforms associated with stylet penetration and feeding in leaf tissues. These waveforms were characteristic of feeding phases corresponding to epidermis penetration pathway, salivation, and ingestion. We calculated 28 parameters (e.g., number of probes, duration of phases, and time spent in the various tissues) to describe and compare the feeding behavior of the Erythroneura species. We conclude that the three Erythroneura species are mainly mesophyll feeders but may probably also feed in other tissues such as xylem.     

Searching and oviposition behavior of a mymarid egg parasitoid, Anagrus nigriventris, on five host plant species of its leafhopper host, Circulifer tenellus

Searching and oviposition behavior and parasitization ability of Anagrus nigriventris Girault (Hymenoptera: Mymaridae), an egg parasitoid of beet leafhopper, Circulifer tenellus (Baker) (Homoptera: Cicadellidae), were examined on five host plant species of beet leafhopper: sugar beet (Beta vulgaris L.), red stem filaree (Erodium cicutarium[L.]), peppergrass (Lepidium nitidum Nuttall), desert plantain (Plantago ovata Forsskal), and London rocket (Sisymbrium irio L.). Beet leafhopper embeds its eggs in the tissues of these plant species. For each plant species, A. nigriventris behavior was examined on plants with and without beet leafhopper eggs. Experimental design was a 5 (plant species) by 2 (host eggs present/absent) factorial. Additionally within each treatment, parasitoid behavior was observed over a 22-h period at five different observation periods: t=0, 3, 6, 9, and 22 h where t=0 h represents initial exposure of the insect with the plant. The behavioral events observed were: `fast walking' (general searching), `slow walking' (intensive searching), ovipositor probing, grooming, feeding, and resting. Significant differences (=0.05) among plant species in time spent on the plant, percentage of host eggs parasitized, and behavioral variables associated with intensive searching and oviposition all indicated that the plant species fell into two groups: `preferred' plants (sugar beet, London rocket, and peppergrass), and `unpreferred' plants (filaree and plantago). These variables also indicated that the parasitoids spent more time on, searched more, probed more, and oviposited more in plants with host eggs than plants without host eggs. Consistent effects of time (over the observation periods from t=0 to t=22 h) generally were detected only in the preferred plant species that had host eggs present. In these cases, intensive searching and probing decreased as time advanced, while variables related to general searching (`fast walking') and abandoning host egg patches (leaving the plant) tended to increase over time.     

Characterization of electrical penetration graphs of Bucephalogonia xanthophis, a vector of Xylella fastidiosa in citrus

The sharpshooter Bucephalogonia xanthophis (Berg) (Homoptera: Cicadellidae) is a vector of the xylem‐limited bacterium, Xylella fastidiosa (Wells, Raju, Hung, Weisburg, Mandelco‐Paul, and Brenner), which causes citrus variegated chlorosis. Despite the importance of citrus variegated chlorosis, the probing behavior of vectors on citrus and its implications for transmission of X. fastidiosa have not been studied. Here we studied electrical penetration graph (EPG‐DC system) waveforms produced by B. xanthophis on Citrus sinensis (L.) Osbeck (Rutaceae), and their relationships with stylet activities and xylem ingestion. Electrical penetration graph waveforms were described based on amplitude, frequency, voltage level, and electrical origin of the observed traces during stylet penetration on plant tissues. The main waveforms were correlated with histological observations of salivary sheaths in plant tissues and excretion analysis, in order to determine stylet activities and their precise position. Six waveforms and associated activities are described: (S) secretion of salivary sheath and intracellular stylet pathway, (R) resting during stylet pathway, (Xc) contact of stylets with xylem vessels, (Xi) active xylem ingestion, (N) interruption within the xylem phase (during Xc or Xi), and (W) withdrawal of stylet from the plant. The sharpshooter spent 91.8% of its probing time with its stylet in the xylem, where the main activity was ingestion (Xi: 97.5%). During a probe, the most likely sequence of events is secretion of salivary sheath and pathway (S) through epidermal and parenchyma cells (all individuals), followed by contact with xylem (Xc) (67.6% of all individuals) and ingestion (Xi) (88.3% of those that exhibit waveform Xc). The mean time to contact the xylem (Xc) and initiate ingestion (Xi) after onset of the first probe was 27.8 and 34.2 min, respectively. However, sustained xylem ingestion (Xi > 5 min) was established after 39.8 min, on average. This information is basic for future studies on the transmission mechanisms of X. fastidiosa and in order to establish control strategies aimed at interfering with this process.     

The effect of plant age and infection with virus yellows on the survival of Myzus persicae on sugar beet

Survival of Myzus persicae confined in clip-cages on mature leaves of sugar beet declined as the plants aged. Death of aphids was often preceded by the appearance of a black deposit in the aphids' stomachs, which may have been the cause of death. Both the rate of death and the proportion of aphids dying with black deposits was significantly less when plants were infected with beet yellows virus or beet mild yellowing virus, by comparison with healthy plants. The implication of these phenomena on the onset of mature plant resistance is discussed.     

Barley yellow dwarf virus, wheat, and Sitobion avenae: a case of trilateral interactions

We analysed interactions in the system of two Barley Yellow Dwarf Virus (BYDV) strains (MAV and PAV), and wheat (cv. Tinos) as host plant for the virus, and the cereal aphid Sitobion avenae (F.) as vector, in particular whether or not infection by the virus might alter host plant suitability in favour of vector development. By measuring the amino acid and sugar content in the phloem sap of infected and non‐infected wheat plants we found a significant reduction in the concentration of the total amount of amino acids on BYDV‐infected plants. Qualitative and quantitative analysis of honeydew and honeydew excretion indicated a lower efficiency of phloem sap utilisation by S. avenae on infected plants. In addition, S. avenae excreted less honeydew on infected plants. Both BYDV strains significantly affected aphid development by a reduction in the intrinsic rate of natural increase. Hence, infection by the virus reduced the host suitability in terms of aphid population growth potential on BYDV‐infected plants. However, more alate morphs developed on virus‐infected plants. These findings are discussed in relation to the population dynamics of S. avenae, and, as a consequence, the spread of BYDV.     

Analysis of tea plant resistance to tea green leafhopper,Empoasca onukii,by detecting stylet‐probing behavior with DC electropenetrography

The tea green leafhopper, Empoasca onukiiMatsuda (Hemiptera: Cicadellidae: Typhlocybinae), is a serious pest of tea plants in East Asia. Previous work has shown that two tea germplasms, Cd19 and Cd289, sustain less hopperburn damage by E. onukii than does Camellia sinensis (L.) O. Kuntze cv. ‘Yabukita’ (Theaceae), and E. onukii excretes less honeydew on these germplasms than on the susceptible Yabukita. This study investigated the feeding behavior of E. onukii with a direct current electropenetrograph (DC EPG) to compare feeding behaviors, including ingestion, on resistant tea germplasms and Yabukita. Feeding behaviors on the resistant germplasms were significantly restricted, with few bouts of active ingestion of short duration and long periods of non‐probing, whereas E. onukii engaged in active ingestion of long duration many times on the susceptible cv. Yabukita. The tea germplasms, Cd19 and Cd289, therefore showed strong resistance to E. onukii. Furthermore, the shape of puncture holes left after probing was compared between the susceptible Yabukita and the resistant germplasms. The puncture holes on Cd19 and Cd289 were indistinct in shape and closed compared with those on Yabukita.     

基于EPG的麦长管蚜、麦二叉蚜和禾谷缢管蚜取食行为比较

麦长管蚜Sitobion avenae (Fabricius),麦二叉蚜Schizaphis graminum (Rondani)和禾谷缢管蚜Rhopalosiphum padi (Linnaeus)虽然都取食小麦,但其取食部位、传毒能力均有差异。利用EPG研究了3种麦蚜在同一寄主植物上的取食行为,结果显示:(1)禾谷缢管蚜在取食过程中G波出现的时间最早,G波总的持续时间和每次刺探G波的平均持续时间都明显长于麦长管蚜和麦二叉蚜。麦长管蚜第1次E1波的时间、E1波总的持续时间和每次刺探E1波的平均持续时间都明显比麦二叉蚜和禾谷缢管蚜要长。麦二叉蚜E2波总的持续时间和每次刺探E2波的平均持续时间都明显长于麦长管蚜和禾谷缢管蚜。表明3种蚜虫各自拥有不同取食策略。禾谷缢管蚜比其它两种蚜虫需要更多的水分和无机盐,麦长管蚜通过分泌大量唾液增大对食物的利用率,麦二叉蚜通过增加韧皮部取食时间以满足对营养的需要。(2)刺探过程中麦二叉蚜pd波出现的次数为(51.97±7.82)次,高于麦长管蚜的(44.73±4.52)次和禾谷缢管蚜的(32.99±4.22)次。麦二叉蚜pd波Ⅱ-2和Ⅱ-3亚波的时间最长,禾谷缢管蚜最短,三者之间差异达显著水平。表明与其它两种麦蚜相比,麦二叉蚜在取食过程中口针与细胞间的接触频率更高,与细胞内获毒和传毒相关的Ⅱ-3波和Ⅱ-2波持续时间更长,增加了获毒和传毒的几率,是其传毒能力最强的机理。     

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.