Stylet Penetration Research Articles

Stylet penetration activities of Diaphorina citri associated with transmission of Candidatus Liberibacter asiaticus

Author(s): Ferreira, C.; Okuma, D. M.; Lopes, J. R.S. | Abstract: The electrical penetration graph (EPG) technique was used to determine Diaphorina citri stylet penetration activities associated with Candidatus Liberibacter asiaticus (Las) acquisition and inoculation in citrus. In a first experiment, healthy D. citri adults were connected to the EPG system and placed on Las-infected plants. Probes were artificially terminated after the following stylet penetration periods and waveforms: I) 20 min in waveform C (pathway phase through epidermis and parenchyma); II) C + 30 s in D (first contact with phloem tissue); III) C+D + 70 s in E1 (penetration and possibly salivation/ingestion in the phloem sieve elements); and IV) C+D+E1+ 1 h in E2 (phloem sap ingestion). The insects were tested for Las infectivity by real-time PCR 3 wks later. In a second experiment, 3rd-instar nymphs were first submitted to an acquisition access period of 2 wks on Las-infected plants and then connected to the EPG system on healthy citrus seedlings during the same stylet penetration periods of the first experiment. D. citri acquired the pathogen only after penetration in the phloem sieve elements and mostly during waveform E2 (27 infective insects of 54 tested). Only 2 of 52 insects exposed to infected plants until waveform E1 (treatment III) were positive. In the second experiment, transmission (by 9 of 50 insects tested) was observed only by psyllids allowed to perform E2 on healthy seedlings. Overall, the data show that both acquisition and inoculation occur during the phloem phase, primarily during sustained sap ingestion (E2). This information is important for designing efficient control tactics aimed at preventing Las transmission by D. citri. Financial support: Citrus Research and Development Foundation, CNPq and Fundecitrus

Control of tomato whiteflies using the confusion effect of plant odours

Glasshouse tomato production is reduced by the whitefly Trialeurodes vaporariorum, a major worldwide pest of glasshouse crops. Whitefly control is achieved using pesticides or parasitoids, which have drawbacks. There is thus a need for other control methods. For instance, the use of volatile compounds from plant odours could profoundly change the behaviour of plant-eating insects. This practice should be safe because plant odours are usually harmless to humans. Therefore, we have studied the effect of plant volatiles on whiteflies feeding on tomato plants. The rationale was to use the confusion effect by supplying whiteflies with a super-abundance of volatiles. We removed plant headspace volatiles from multiple whitefly host plants. Then, we presented these volatiles to whiteflies feeding on tomato plants. At the same time, whitefly stylet penetration is monitored using electrical penetration graphs (EPG). Plant colonisation, egg laying and honeydew production are analysed in separate experiments. Data are compared to controls in which extracted volatiles from tomato and air alone are presented to the whiteflies. The only significant effect produced by exposure to multiple-host volatiles is a pronounced reduction in the incidence of phloem-related waveforms during the 15-h EPG recording. This represents a delay in, rather than a cessation of, phloem-related activities as there is no related reduction in long-term performance. The confusion effect thus does not appear to exert strong effects on whitefly behaviour here.

Characterization and Correlation of EPG Waveforms of Bactericera Cockerelli (Hemiptera: Triozidae): Variability in Waveform Appearance in Relation to Applied Signal

AbstractThe tomato-potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae), was recently shown to be a vector of “Candidatus Liberibacter solanacearum” (Lso), a phloem-limited bacterium that is the putative causal agent of “zebra chip” in potato and unnamed diseases in other solanaceous species. Despite its importance, very little is known about B. cockerelli stylet probing behaviors that control transmission of Lso to its host plants. Herein, we report the first study characterizing the electrical penetration graph waveforms representing stylet penetration behaviors of the B. cockerelli feeding on potato. Waveforms produced by adult B. cockerelli on potato were also correlated using light microscopy of salivary sheath termini in plant tissue after probes were artificially terminated during the identified waveforms. In addition, behavioral activities were inferred based on electrical origins of waveforms as well as similarities in waveform appearances with those of other psyllids, aphids, and whiteflies. Adult B. cockerelli produced six waveform families and four types, which represent the following proposed biological meanings: family A, initial penetration and sheath salivation; family B, penetration of epidermal cells; family C, secretion of most of the salivary sheath and stylet pathway in mesophyll and parenchyma, with two types, C1 and C2, of unknown meaning; family D, initial contact with phloem cells; family E, activities in phloem cells, with two types, El, putative phloem salivation, and E2, phloem sap ingestion; and family G, xylem ingestion. In addition, a previously unreported variant of waveform G was characterized and correlated with applied signal type. Variation in D and G waveform appearances was correlated with polarity, type, and magnitude of applied signal. Results suggest that active phloem sap ingestion during E2 may play a critical role in acquisition of Lso bacterial cells. E1 may be important in inoculation of the bacterium into phloem sieve elements because it may represent salivation into phloem sieve elements. Analysis of B. cockerelli waveforms could lead to faster development of resistant host plant varieties, strengthen integrated pest management strategies by incorporating alternative plant hosts, and maximize the efficiency of pesticides.

Stylet penetration behaviors of Myzus persicae (Hemiptera: Aphididae) on four Ipomoea spp. infected or noninfected with sweet potato potyviruses.

Myzus persicae (Sulzer) is an efficient vector of potyviruses in sweet potato, Ipomoea batatas (L.). These potyviruses also infect members of the morning glory family Ipomoea cordatotriloba Dennstedt and Ipomoea hederacea Jacqin commonly found within or around sweet potato fields. Infection of sweet potato with potyviruses increases the intrinsic rate of increase of M. persicae. Thus, from the epidemiological stand point, virus infection can modify vector population dynamics, and therefore increase virus spread. To better understand this, stylet penetration behaviors of M. persicae on virus infected and noninfected sweet potato cvs. 'Beauregard' and 'Evangeline', as well as morning glory plants I. cordatotriloba and I. hederacea were monitored. Stylet penetration behaviors associated with nonpersistent virus transmission such as time to first intracellular puncture (potential drop), number of potential drops, duration of potential drop, duration of potential drop subphase II-3, and number of potential drops with subphase II-3 pulses were significantly increased on virus-infected compared with noninfected Beauregard, but greatly reduced on virus-infected compared with noninfected I. hederacea plants. Stylet penetration behaviors associated with host acceptance such as reduced nonprobing duration and nonprobing events were greater on virus-infected compared with noninfected Beauregard plants. In contrast, on Evangeline, I. cordatotriloba and I. hederacea stylet penetration behaviors by M. persicae indicate it had less preference for virus-infected compared with noninfected plants.

Stylet penetration activities linked to the acquisition and inoculation of Candidatus Liberibacter solanacearum by its vector tomato potato psyllid

AbstractThe tomato potato psyllid (TPP), Bactericera cockerelli (Sulc) (Hemiptera: Triozidae), is the main vector of the bacterium Candidatus Liberibacter solanacearum (Lso), a major disease of solanaceous crops. Feeding of TPP is associated with Lso transmission. However, very little is known about the stylet penetration activities linked to acquisition and inoculation of Lso. The electrical penetration graph (EPG)‐DC system was used to monitor stylet penetration activities during acquisition and inoculation of Lso by individual TPP on tomato [Solanum lycopersicum L. (Solanaceae)]. Female TPP from Lso‐free and Lso‐infected colonies were used in acquisition and inoculation tests, respectively. In the acquisition tests, TPP were tested for Lso after EPG recording of their stylet penetration activities on Lso‐infected tomato shoots. In the inoculation tests, samples from the tomato plants on which the stylet penetration of Lso‐infected TPP had been recorded were tested for Lso infection. The relationships between qPCR results and the EPG waveforms (C, G, D, E1, and E2) representing the main stylet penetration activities performed by individual insects in inoculation and acquisition tests were investigated. Results confirmed that a single adult TPP is capable of infecting a plant with Lso. Our data suggest that acquisition of the bacteria occurs during phloem ingestion (E2), and inoculation is likely associated with salivation into the phloem sieve elements (E1). The durations of EPG parameters were not significantly different between Lso‐infected and Lso‐free TPP (later shown by qPCR) in acquisition tests. In inoculation tests, the durations of E1 or E2 recorded from TPP on Lso‐infected and Lso‐free plants that were later shown by qPCR were not significantly different. However, C was shorter on Lso‐infected plants than on Lso‐free plants, where TPP performed phloem activities. The minimum plant access period required for Lso transmission by a single TPP was estimated to be ca. 2 h, with an acquisition threshold of about 36 min.

Effects of Thiamethoxam Seed Treatments on Soybean Aphid (Hemiptera: Aphididae) Feeding Behavior

Since its discovery in North America in 2000, the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), has rapidly become an important pest of soybean [Glycine max (L.) Merrill], sometimes resulting in significant yield losses. Previous research has documented the toxicity of neonicotinoid seed treatments to soybean aphids, but control under field conditions has been inconsistent. Imidacloprid, a popular neonicotinoid insecticide, has been shown to exhibit antifeedant effects on aphids. Antifeedant activity has not been demonstrated for other neonicotinoids, including thiamethoxam. This research investigated the effects of a thiamethoxam seed treatment on soybean aphid feeding behavior by using electronic penetration graphs (EPG) to visualize stylet penetration behavior. Soybean aphid feeding behavior was assessed for 9 h on thiamethoxam-treated and untreated soybeans (V2 and V4 stages). Because results were inconclusive from initial experiments, a study was conducted to document the effects of thiamethoxam-treated soybeans on soybean aphid survival. The seed treatment was shown to negatively affect aphid survival at 4, 8, and 11 d after aphid introduction. A subsequent EPG study then was designed to document soybean aphid feeding behavior for 15 h, after an initial exposure of 9 h to thiamethoxam-treated soybeans. In this study, the exposed aphids exhibited significant differences in feeding behavior compared with those aphids feeding on untreated soybeans. Soybean aphids on thiamethoxam-treated soybeans spent significantly less time feeding in the sieve element phase, with a greater duration of nonprobing events. These studies suggest soybean aphids are unable to ingest phloem sap, which may be another important element in seed treatment protection.

Feeding Behavior Comparison of Soybean Aphid (Hemiptera: Aphididae) Biotypes on Different Soybean Genotypes

Soybean aphids have become a serious pest of soybean, Glycine max L. (Merrill), since they were first detected in North America in 2000. Three soybean aphid biotypes have been documented in the United States in the last 10 yr, but few studies have been done on their feeding behavior in the United States The Electrical Penetration Graph is a convenient and successful tool to study the feeding behavior of piercing and sucking insects. This is the first attempt to study the feeding behavior differences between biotype 1 and biotype 2 on soybean genotypes using the Electrical Penetration Graph technique, and includes both resistant and susceptible soybean genotypes from Kansas and Michigan. The experiments were run for 9 h each for each genotype with a total of eight channels at a time. Results indicated that aphids feeding on susceptible genotypes had a significantly greater duration of sieve element phase than when feeding on resistant genotypes. Furthermore, the time taken to reach the first sieve element phase in resistant genotypes was significantly greater than in susceptible genotypes. Most of the aphids reached sieve element phase (> 90%) in susceptible genotypes, but only a few (< 30%) reached sieve element phase in resistant genotypes during the 9-h recording period; however, we found no differences in any other probing phases between resistant and susceptible genotypes except the number of potential drops in biotype 2. Thus, the resistance was largely associated with phloem tissues. Therefore, some biochemical, physical, or morphological factors could affect stylet penetration of aphids.

Influence of Citrus Plants Infected withXylella fastidiosaon Stylet Penetration Activities ofBucephalogonia xanthophis(Hemiptera: Cicadellidae)

AbstractXylem colonization by Xylello fastidiosa promotes physiological, biochemical, and morphological alterations in citrus plants causing citrus variegated chlorosis (CVC) disease, which might influence the feeding behavior of vectors of this bacterial pathogen and its spread in citrus groves. By using the electrical penetration graph technique, we compared the numbers and durations of stylet penetration activities by adults of the sharpshooter vector Bucephalogonia xanthophis (Berg) (Hemiptera: Cicadellidae) on healthy and X. fastidiosa-infected sweet orange seedlings (Citrus sinensis (L.) Osbeck, cv. Pera). Infected plants were either symptomatic, exhibiting the typical CVC, symptoms or totally asymptomatic. The mean time needed to contact xylem and start xylem sap ingestion after the onset of the first probe was similar among treatments. However, the average time elapsed between the onset of the first probe and the beginning of sustained xylem ingestion (&amp;gt;5 min) was longer on plants with CVC symptoms than on infected asymptomatic or healthy plants. In addition, the length of time spent in ingestion activities was much shorter on symptomatic plants. Our results showed that CVC symptomatic citrus plants were a less acceptable host than uninfected or asymptomatic X. fastidiosa-infected plants. Furthermore, our results support the hypothesis that symptomless infected citrus trees may be more important as sources for CVC spread than severely diseased ones.

Feeding behaviour and performance of different populations of the black currant‐lettuce aphid, Nasonovia ribisnigri, on resistant and susceptible lettuce

AbstractWhen crops are bred for resistance to herbivores, these herbivores are under strong selection pressure to overcome this resistance, which may result in the emergence of virulent biotypes. This is a growing problem for crop species attacked by aphids. The Nr‐gene in lettuce confers near‐complete resistance against the black currant‐lettuce aphid, Nasonovia ribisnigri (Mosely) (Hemiptera: Aphididae). Since 2007, populations of N. ribisnigri have been reported in several locations in Europe to infest resistant lettuce varieties that possess the Nr‐gene. The objective of this study was to analyse the behaviour and level of virulence of several N. ribisnigri populations observed to have colonized Nr‐locus‐containing lettuce lines. We analysed the stylet penetration and feeding behaviour, and the performance of these N. ribisnigri populations on resistant and susceptible lettuce lines. Large variation in the degree of virulence to the Nr‐locus‐containing lettuce lines was found among populations of the Nr:1 biotype. The German population was highly virulent on the Nr‐containing resistant lettuce lines, and showed similar feeding behaviour and performance on both the susceptible and resistant lettuces. The French population from Paris was the second most virulent, though reproduction on the resistant lines was reduced. The French population from Perpignan and a population from Belgium, however, showed reduced performance and feeding rate on the resistant compared to the susceptible lettuces. The lettuce background in which the Nr‐gene is expressed influences the level of resistance to the various Nr:1 aphid populations, because the performance and feeding behaviour differed between the aphids on the cultivars (romaine lettuce) compared to the near‐isogenic lines (butterhead/iceberg lettuce). This study also shows that being able to feed on a plant not automatically implies that a population can successfully develop on that plant, because aphids showed phloem ingestion during the 8‐h recording period on resistant lettuce, but were not able to survive and reproduce on the same lettuce line.

Stylet Morphometrics and Citrus Leaf Vein Structure in Relation to Feeding Behavior of the Asian Citrus Psyllid Diaphorina citri, Vector of Citrus Huanglongbing Bacterium

The Asian citrus psyllid (ACP), Diaphorina citri (Hemiptera: Psyllidae), is the primary vector of the phloem-limited bacterium Candidatus Liberibacter asiaticus (LAS) associated with huanglongbing (HLB, citrus greening), considered the world’s most serious disease of citrus. Stylet morphometrics of ACP nymphs and adults were studied in relation to citrus vein structure and to their putative (histologically verified) feeding sites on Valencia orange leaves. ACP nymphs preferred to settle and feed on the lower (abaxial) side of young leaves either on secondary veins or on the sides of the midrib, whereas adults preferred to settle and feed on the upper (adaxial) or lower secondary veins of young or old leaves. Early instar nymphs can reach and probe the phloem probably because the distance to the phloem is considerably shorter in younger than in mature leaves, and is shorter from the sides of the midrib compared to that from the center. Additionally, the thick-walled ‘fibrous ring’ (sclerenchyma) around the phloem, which may act as a barrier to ACP stylet penetration into the phloem, is more prominent in older than in younger leaves and in the center than on the sides of the midrib. The majority (80–90%) of the salivary sheath termini produced by ACP nymphs and adults that reached a vascular bundle were associated with the phloem, whereas only 10–20% were associated with xylem vessels. Ultrastructural studies on ACP stylets and LAS-infected leaves suggested that the width of the maxillary food canal in first instar nymphs is wide enough for LAS bacteria to traverse during food ingestion (and LAS acquisition). However, the width of the maxillary salivary canal in these nymphs may not be wide enough to accommodate LAS bacteria during salivation (and LAS inoculation) into host plants. This may explain the inability of early instar nymphs to transmit LAS/HLB in earlier reports.

Characterization of Antibiosis and Antixenosis to the Woolly Poplar Aphid (Hemiptera: Aphididae) in the Bark of Different Poplar Genotypes

The woolly poplar aphid, Phloeomyzus passerinii (Signoret) (Hemiptera: Aphididae), is a major pest of poplar plantations in the Mediterranean basin and the Near East. Aphids colonize poplar trunks and feed upon the cortical parenchyma. Despite the economic importance of poplar, little is known about the mechanisms involved in poplar resistance to this pest. However, Populus x canadensis Moench genotypes show various levels of resistance to P. passerinii. This study has investigated the type of poplar resistance (antibiosis or antixenosis) by assessing aphid settlement, physiology (survival, development, and reproduction), and stylet penetration behavior (electrical penetration graph) on three P. x canadensis genotypes; '1214' (susceptible), 'Brenta' (resistant), and '145/51' (intermediate). Because settlement was reduced, the highly resistant genotype Brenta exhibited surface antixenosis. In addition, nymphal survival was null on Brenta, and twice less adult aphid initiated a sustained intracellular phase in the cortical parenchyma of that genotype compared with the other two genotypes. Thus, Brenta also showed parenchyma-located antixenosis coupled with antibiosis characteristic. In contrast, P. passerinii had no difficulty to initiate a sustained ingestion in the cortical parenchyma of the intermediate genotype 145/51, but decreased fecundity and lower intrinsic rate of natural increase were clear expressions of antibiosis.

How phloem-feeding insects face the challenge of phloem-located defenses.

Due to the high content of nutrient, sieve tubes are a primary target for pests, e.g., most phytophagous hemipteran. To protect the integrity of the sieve tubes as well as their content, plants possess diverse chemical and physical defense mechanisms. The latter mechanisms are important because they can potentially interfere with the food source accession of phloem-feeding insects. Physical defense mechanisms are based on callose as well as on proteins and often plug the sieve tube. Insects that feed from sieve tubes are potentially able to overwhelm these defense mechanisms using their saliva. Gel saliva forms a sheath in the apoplast around the stylet and is suggested to seal the stylet penetration site in the cell plasma membrane. In addition, watery saliva is secreted into penetrated cells including sieve elements; the presence of specific enzymes/effectors in this saliva is thought to interfere with plant defense responses. Here we detail several aspects of plant defense and discuss the interaction of plants and phloem-feeding insects. Recent agro-biotechnological phloem-located aphid control strategies are presented.

Stylet penetration behaviour of Pseudococcus longispinus in relation to acquisition of grapevine leafroll virus 3

Grapevine leafroll–associated virus-3 (GLRaV-3) is transmitted from infected grapevines to healthy vines by mealybugs. The stylet penetration behaviour of Pseudococcus longispinus (Hemiptera: Pseudococcidae) was electronically monitored on leaves of grape plants to quantify the time taken to access the phloem and the duration of phloem ingestion. More of the first instar nymphs than of the adults showed sustained (>10 min) phloem ingestion; however, nymphs were affected adversely by longer monitoring periods. The probing and phloem ingestion periods of adults on GLRaV-3-infected Red Globe and uninfected Pinot noir were not significantly different from each other. Most adults showed the first phloem ingestion and the first sustained phloem ingestion after 12 h and after 24 h of their first probe, respectively. Free (unwired) and electrical penetration graph (EPG)-monitored (wired) P. longispinus adults were tested for acquisition of virus after different acquisition access periods (AAP). Acquired GLRaV-3 RNA in extracts of whole insects was detected by reverse transcription and polymerase chain reaction amplification. For the unwired adult mealybugs, 30 % that had an AAP of 48 h and 90 % that had an AAP of 72 or 96 h were positive for GLRaV-3. Five out of 24 (21 %) of the wired mealybugs allowed at least 24 h APP (1.8–44.4 h of phloem ingestion) were positive for GLRaV-3. None of the adult mealybugs acquired virus during the first 24 h of AAP. We conclude that GLRaV-3 acquisition by P. longispinus generally occurs within 24–72 h AAP with as little as 1.8 h of phloem ingestion.

Pattern of Stylet Penetration Activity byHomalodisca vitripennis(Hemiptera: Cicadellidae) Adults in Relation to Environmental Temperature and Light Conditions

Effects of ambient spring air temperature and light intensity on stylet penetration activities of the glassy-winged sharpshooter, Homalodisca vitripennis (Germar), were studied under field conditions by using an electrical penetration graph. Electrical penetration graph waveforms representing salivary sheath formation and searching (pathway phase), xylem contact (X waves), and ingestion of xylem fluid (waveform C) were analyzed. Previous research supported the concept that acquisition of Xylella fastidiosa, the Pierce's disease bacterium, occurs during ingestion, whereas inoculation occurs during xylem contact periods (X waves). Diel patterns of H. vitripennis stylet activity showed that, regardless of light condition, xylem ingestion occurred for the longest duration when temperature remained above the feeding threshold (10°C), and only occurred at temperatures below the threshold when ingestion was continued from a preceding, warmer time. Regression analysis indicated that mean waveform durations per insect (WDI) for combined stylet activities (pathway and ingestion) as well as X wave frequencies were significantly influenced by temperature, but there was no significant impact of light intensity or interaction between temperature and light intensity. The relationship between temperature and stylet activities in terms of WDI and X wave frequency was described using linear and nonlinear models. Validation of the nonlinear models indicated that they well predicted the WDIs for both ingestion and combined stylet activities, using temperature only as a single input. Overall, findings clearly demonstrate that temperature is an important factor that influences the H. vitripennis feeding behaviors responsible for transmission (acquisition and inoculation) of the Pierce's disease bacterium, with implications for vector ecology and management, as well as disease epidemiology.

Probing behaviour of Cacopsylla pyri on a resistant pear selection

AbstractEuropean 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 (&gt;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.

Mouthparts and stylet penetration of the lac insect Kerria lacca (Kerr) (Hemiptera:Tachardiidae)

Hitherto less known aspects on mouthpart morphology and penetration mechanism of the lac insect Kerria lacca have been explored. Unique details of the mouthparts, i.e. morphology of labium and stylets and salivary sheath have been brought out. The gross morphology of the mouthparts though resembled other plant sucking homopterans; a two-segmented labium with symmetrically distributed six pairs of contact-chemoreceptors on its surface was distinct; the mandibular stylets had serrations on its extreme apical region, while the maxillary stylets had their external surface smooth with parallel longitudinal grooves on their inner surface. Formation of flanges, salivary sheath and penetration pathway observed along with probing and penetration of the stylets intracellularly up to the phloem cells, as illustrated herein, are the addition to the existing knowledge on the structural details of the mouthparts and the feeding behavior thereupon.

EPG waveform characteristics of solenopsis mealybug stylet penetration on cotton

AbstractThe solenopsis mealybug, Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae), is a polyphagous insect known to cause severe damage to cotton (especially transgenic varieties) in South Asia, and currently poses a serious threat in Asia and potentially elsewhere. Stylet penetration behavior of P. solenopsis on cotton was monitored using the electrical penetration graph (EPG) technique (DC system) and the EPG characteristics were compared with those previously published from Phenacoccus manihoti Matile‐Ferrero and Planococcus citri (Risso). We identified and further characterized typical waveforms of A, B, C, and pd (together pathway), E1 and E2 (phloem), F (derailed stylet mechanics), and G (xylem). Five novel EPG aspects were distinguished in the EPG waveforms from P. solenopsis: (1) obvious B waveforms occurred following waveform A, (2) during waveform C, some aphid‐like E1e waveforms were observed, (3) prolonged potential drops (pd) up to &gt;1 h occurred with two continuously alternating sub‐phases pd1 and pd2, (4) the pd1 waveform always occurred as the first waveform related to phloem sieve elements, preceding the other phloem waveforms (E), the labeling of which we changed to achieve a better comparison to the aphid E waveforms, and (5) waveform F, related to derailed stylet mechanics occurred but was not reported from other mealybugs so far. This is mainly a waveform morphology study to extend existing knowledge on mealybug EPGs to investigate mealybug‐host plant interactions. Further experimental verification of waveform correlations with plant tissue positions of stylet tips and insect activities is still needed.

Feeding disruption of potato psyllid, Bactericera cockerelli, by imidacloprid as measured by electrical penetration graphs

AbstractThe potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae), is a serious pest of potatoes that can cause yield loss by direct feeding and by transmitting a bacterial pathogen, Candidatus Liberibacter psyllaurous (also known as Candidatus L. solanacearum), which is associated with zebra chip disease of this crop. Current pest management practices rely on the use of insecticides for control of potato psyllid to lower disease incidences and increase yields. Imidacloprid is typically applied at potato planting, and it remains unknown if imidacloprid has any effect on potato psyllid feeding behavior. Thus, our specific objectives of this study were to determine and characterize the effects of imidacloprid treatment (0.11 ml l−1) to potato plants on adult potato psyllid feeding behavior 1, 2, and 4 weeks post‐application. Electrical penetration graph (EPG) recordings of potato psyllid feeding revealed six EPG waveforms, which include non‐probing (NP), intercellular stylet penetration (C), initial contact with phloem tissue (D), salivation into phloem sieve elements (E1), phloem sap ingestion (E2), and ingestion of xylem sap (G). The number of NP events and the duration of individual NP events significantly increased on plants treated with imidacloprid compared with untreated controls. Potato psyllids exhibited significant decreases in the number of phloem salivation events on plants treated with imidacloprid. Waveform durations and waveform durations per event for E2 and G were significantly decreased for psyllids on plants treated with imidacloprid compared with untreated controls. These data suggest that the effective use of imidacloprid to reduce transmission of Ca. Liberibacter psyllaurous is related to the negative effects of imidacloprid on psyllid feeding.

Stylet penetration of Cacopsylla pyri; an electrical penetration graph (EPG) study

Detailed information on plant penetration activities by pear psylla Cacopsylla pyri L. (Hemiptera Psyllidae) is essential to study phytoplasma transmission of “ Candidatus Phytoplasma pyri” responsible of pear decline disease (PD) and to trace and evaluate resistant traits in new pear tree selections for advanced breeding programs. The electrical penetration graph technique or (full) EPG may relevantly contribute to this knowledge. C. pyri EPG waveforms were characterized on basis of amplitude, frequency, voltage level, and electrical origin. Additionally, stylet tracks and the putative location of stylet tips in the plant tissue were histologically related to EPG waveforms by light and transmission electron microscopy observations after stylectomy. More than one waveform occurred in the same tissue: PA, PB, PC1 and PC2 were all detected in the mesophyll, and PE1 and PE2 were both recorded in the phloem. Waveform PE1 was always preceded by transient waveform PD, as previously described in other psyllids. Interestingly, no brief intracellular punctures (potential drop waveforms) were observed during plant penetration, opposite of what is usually recorded in aphids and other Sternorrhyncha.

Estimating potential stylet penetration of southern green stink bug - a mathematical modeling approach

Southern green stink bugs, Nezara viridula (L.) (Hemiptera: Pentatomidae), and related species are significant pests of cotton, Gossypium hirsutum L. (Malvaceae), in the USA Cotton Belt. Using their stylets, adults introduce pathogens of cotton into cotton bolls, and preliminary data indicate nymphs can also ingest these pathogens. However, data are lacking regarding stylet penetration potential of N. viridula nymphs, and records of stylet penetration by adults are typically determined after damage has occurred. In this study, rostral segments of all developmental stages of N. viridula were measured to estimate potential stylet penetration depth using a novel mathematical model. Overall mean stylet penetration estimates for all stages ranged from 135.3 μm for first instars to 2 389.3 μm for adult females. Potential stylet penetration significantly increased as the insect progressed through nymphal stages. Penetration was also significantly affected by insect posture while feeding. Overall minimum and maximum observed lengths of rostrum ranged from 835.3 μm (first instars) to 7 088.2 μm (adult females), and mean rostral lengths were significantly different between all stages. This report establishes conservative baselines of potential stylet penetration depths by all nymphal stages and both adult sexes of N. viridula. Additionally, the model presented here can be used to estimate potential stylet penetration for other Hemiptera and closely related insects with similar modes of feeding. In conjunction with crop phenology data, accurate estimates of potential stylet penetration will allow more proactive approaches to pest management in a wide range of high-value cash crops affected worldwide by N. viridula.