Electrical Penetration Graph Recordings Research Articles

Hormetic effects of thiamethoxam on Schizaphis graminum: demographics and feeding behavior

In agroecosystems, insects contend with chemical insecticides often encountered at sublethal concentrations. Insects’ exposure to these mild stresses may induce hormetic effects, which has consequences for managing insect pests. In this study, we used an electrical penetration graph (EPG) technique to investigate the feeding behavior and an age-stage, two-sex life table approach to estimate the sublethal effects of thiamethoxam on greenbug, Schizaphis graminum. The LC5 and LC10 of thiamethoxam significantly decreased longevity and fecundity of directly exposed adult aphids (F0). However, the adult longevity, fecundity, and reproductive days (RPd)—indicating the number of days in which the females produce offspring – in the progeny generation (F1) exhibited significant increase when parental aphids (F0) were treated with LC5 of the active ingredient. Subsequently, key demographic parameters such as intrinsic rate of increase (r) and net reproductive rate (R0) significantly increased at LC5 treatment. EPG recordings showed that total durations of non-probing (Np), intercellular stylet pathway (C), and salivary secretion into the sieve element (E1) were significantly increased, while mean duration of probing (Pr) and total duration of phloem sap ingestion and concurrent salivation (E2) were decreased in F0 adults exposed to LC5 and LC10. Interestingly, in the F1 generation, total duration of Np was significantly decreased while total duration of E2 was increased in LC5 treatment. Taken together, our results showed that an LC5 of thiamethoxam induces intergenerational hormetic effects on the demographic parameters and feeding behavior of F1 individuals of S. graminum. These findings have important implications on chemical control against S. graminum and highlight the need for a deeper understanding of the ecological consequences of such exposures within pest management strategies across the agricultural landscapes.

Feeding behavior and hormoligosis associated with imidacloprid resistance in Asian citrus psyllid, Diaphorina citri.

Imidacloprid is a neonicotinoid insecticide used for managing the Asian citrus psyllid, Diaphorina citri Kuwayama, which serves as vector of phytopathogens causing citrus greening. However, development of resistance to neonicotinoids among populations of D. citri has coincided with occasional control failures in the field. The objectives of this research were to (1) survey current levels of imidacloprid resistance in Florida citrus; (2) compare feeding behavior between imidacloprid-resistant and susceptible D. citri using electrical penetration graph recordings, and (3) investigate the possible amplification of insecticide hormoligosis associated with resistance. Field surveys confirmed that the susceptibility of D. citri populations to imidacloprid has decreased in commercial Florida citrus groves compared with a laboratory-susceptible population. Following 12 generations of selection, resistance to imidacloprid increased by 438 fold compared with the susceptible strain. Imidacloprid-susceptible D. citri feeding on citrus exhibited significantly more bouts associated with intercellular pathway (C), phloem penetration (D), phloem salivation (E1), and nonprobing (Np) activities than imidacloprid-resistant counterparts. However, there were no differences observed in the frequency or duration of phloem ingestion or xylem feeding between susceptible and resistant D. citri. There was no statistical difference in fecundity between resistant and susceptible strains. However, the fecundity of imidacloprid-susceptible female D. citri treated with a sublethal concentration of imidacloprid (LC25) increased significantly compared with controls, while such hormoligosis was less pronounced among imidacloprid-resistant psyllids. Our results suggest that imidacloprid-resistant psyllids may cease feeding sooner than susceptible counterparts following sublethal exposure to this insecticide, indicative of a behavioral resistance mechanism.

Sublethal concentrations of pymetrozine reduce Sogatella furcifera transmission of Southern rice black-streaked dwarf virus.

The transmission of plant viruses is closely associated with the specific probing behaviors of the vectors. Pymetrozine is a pyridine azomethine insecticide that interferes with nervous regulation of feeding behavior of piercing-sucking insects. This study aimed to evaluate the potential of sublethal concentrations of pymetrozine in reducing the transmission of Southern rice black-streaked dwarf virus (SRBSDV) by the planthopper Sogatella furcifera. Laboratory assays showed that both acquisition and inoculation rates of SRBSDV decreased significantly in the planthoppers feeding on plants treated with lethal concentrations 10% and 50% (LC10 and LC50 ) pymetrozine compared with the insects feeding on the control plants, for which significant effects of pymetrozine concentration and time post-treatment were detected. Honeydew excretion of the planthoppers showed significant reduction with increasing concentration of the insecticide but no significant association with time post-treatment. Electrical penetration graph recordings revealed that total durations of each waveform in both acquisition and inoculation were significantly affected by pymetrozine treatment, with total durations of non-probing (NP), penetration initiation (N1), and extracellular activity (N3) elongated whereas those of salivation (N2) and phloem-related activities (N4-a and N4-b) shortened. Additionally, both acquisition and inoculation rates were significantly lower at 168 h than at 6 h post-treatment. The results indicate that sublethal concentrations of pymetrozine reduce SRBSDV transmission, which is associated with reduction in feeding and alteration in probing behaviors characterized by the prolonged non-probing, penetration initiation and extracellular activity and shortened salivation and phloem-related activities. © 2023 Society of Chemical Industry.

Survival and Feeding Behavior of Diaphorina citri (Hemiptera: Liviidae) Adults on Common Cover Crops in Citrus

Asian citrus psyllid, Diaphorina citri, transmits Candidatus Liberibacter asiaticus (CLas), the bacterial pathogen responsible for citrus greening disease. To explore the possibility that cover crops in citrus groves may serve as refuges for this pathogen vector during unfavorable host conditions, psyllid feeding was investigated on six common cover crop species and citrus using electrical penetration graph (EPG) recordings and behavioral bioassays. EPG recordings showed that the proportion of time spent by D. citri feeding on xylem was similar or higher on all tested cover crops (17%–32%) compared to the positive control (12%), the preferred host, Citrus macrophylla. Very little to no phloem feeding was observed on cover crops by the adults. In the choice assays, more D. citri adults settled on buckwheat (Fagopyrum esculentum) and cowpea (Vigna unguiculata) than on the host, C. macrophylla, 24 h after release. No-choice assays showed that the citrus cover crop species evaluated extend the survival of D. citri up to 8 d because of xylem feeding. Our results indicate that some cover crop species may be less suitable refuge sites for D. citri than others, but none served as breeding sites or supported more than 8 d of survival.

Evaluation of resistance to black bean aphid (Aphis fabae) in selected varieties and mutant genotypes of common bean (Phaseolus vulgaris)

AbstractCommon bean (Phaseolus vulgaris) is an important food crop across sub‐Saharan Africa. In Zambia, actual common bean yields are typically lower than potential yields because of the impact of invertebrate pests and plant diseases. Black bean aphids (Aphis fabae) (Hemiptera: Aphididae) negatively impact bean productivity directly by ingesting plant assimilates and indirectly by vectoring diseases such as bean common mosaic virus. Current breeding programmes aim to develop bean cultivars with improved yield and tolerance to pests. The objective of this study was to screen five common bean varieties (Rozi Koko, Mwezi Moja, Majesty, KK25 and AO‐1012‐29‐3A) and four mutation‐derived genotypes (CA 3, CA 15, CA 24 and CA 38) for resistance to black bean aphid. Commercial bean cultivars such as Kabulangeti and Carioca (variety from which all mutants were derived) were used as controls for the selected varieties and mutant genotypes, respectively. Several parameters of aphid resistance traits were assessed. Deterrence to aphid was assessed by settling preference while physical barriers to aphid feeding were evaluated by nymph survival. Reduction in palatability of phloem sap was evaluated by nymph development and mean relative growth rate. Electrical penetration graph recordings of feeding behaviour were performed in order to localise aphid‐resistant factors. Nymph development was significantly longer on AO‐1012‐29‐3A compared to Kabulangeti despite the fact that there were significantly fewer glandular trichomes on this line. The variety AO‐1012‐29‐3A can be used in genetic improvement of common bean for aphid resistance.

Virus Infection and Host Plant Suitability Affect Feeding Behaviors of Cannabis Aphid (Hemiptera: Aphididae), a Newly Described Vector of Potato Virus Y.

Aphids are the most prolific vectors of plant viruses resulting in significant yield losses to crops worldwide. Potato virus Y (PVY) is transmitted in a non-persistent manner by 65 species of aphids. With the increasing acreage of hemp (Cannabis sativa L.) (Rosales: Cannabaceae) in the United States, we were interested to know if the cannabis aphid (Phorodon cannabis Passerini) (Hemiptera: Aphididae) is a potential vector of PVY. Here, we conduct transmission assays and utilize the electrical penetration graph (EPG) technique to determine whether cannabis aphids can transmit PVY to hemp (host) and potato (non-host) (Solanum tuberosum L.) (Solanales: Solanaceace). We show for the first time that the cannabis aphid is an efficient vector of PVY to both hemp (96% transmission rate) and potato (91%) using cohorts of aphids. In contrast, individual aphids transmitted the virus more efficiently to hemp (63%) compared to potato (19%). During the initial 15 min of EPG recordings, aphids demonstrated lower number and time spent performing intracellular punctures on potato compared to hemp, which may in part explain low virus transmission to potato using individual aphids. During the entire 8-hour recording, viruliferous aphids spent less time ingesting phloem compared to non-viruliferous aphids on hemp. This reduced host acceptance could potentially cause viruliferous aphids to disperse thereby increasing virus transmission. Overall, our study shows that cannabis aphid is an efficient vector of PVY, and that virus infection and host plant suitability affect feeding behaviors of the cannabis aphid in ways which may increase virus transmission.

SLI1 confers broad-spectrum resistance to phloem-feeding insects.

Resistance (R) genes usually compete in a coevolutionary arms race with reciprocal effectors to confer strain‐specific resistance to pathogens or herbivorous insects. Here, we investigate the specificity of SLI1, a recently identified R gene in Arabidopsis that encodes a small heat shock‐like protein involved in resistance to Myzus persicae aphids. In a panel with several aphid and whitefly species, SLI1 compromised reproductive rates of three species: the tobacco aphid M. persicae nicotianae, the cabbage aphid Brevicoryne brassicae and the cabbage whitefly Aleyrodes proletella. Electrical penetration graph recording of aphid behaviour, revealed shorter salivations and a 3‐to‐5‐fold increase in phloem feeding on sli1 loss‐of‐function plants. The mustard aphid Lipaphis erysimi and Bemisia tabaci whitefly were not affected by SLI1. Unlike the other two aphid species, L. erysimi exhibited repetitive salivations preceding successful phloem feeding, indicating a role of salivary effectors in overcoming SLI1‐mediated resistance. Microscopic characterization showed that SLI1 proteins localize in the sieve tubes of virtually all above‐ and below‐ground tissues and co‐localize with the aphid stylet tip after penetration of the sieve element plasma membrane. These observations reveal an unconventional R gene that escapes the paradigm of strain specificity and confers broad‐spectrum quantitative resistance to phloem‐feeding insects.

Increased probing activities of green peach aphid (GPA), Myzus persicae, on chitosan-treated caisim (Brassica juncea) monitored by electrical penetration graph (EPG)

Green peach aphid (GPA), Myzus persicae, is a major pest of most horticulture crops. Chitosan-based pest management emerges as an alternative to pesticides due to its biocompatibility and biodegradability properties. Population growth and electrical penetration graph (EPG)-based feeding behavior studies were conducted to assess the effect of chitosan application on caisim against GPA at three concentrations (0.1%, 0.5%, and 1%) including two controls of water and acetic acid. Evident GPA population growth reduction was observed in the chitosan-treated caisim. The effect of chitosan was further monitored by 10 h of EPG recording, which revealed a significant increase in probing activities due to frequent stylet withdrawal that generated high levels of short probing activities. Additionally, inter- and intracellular stylet punctures (waveform C and potential drop-Pd, respectively) displayed a significant increase. However, once the stylet reached the phloem tissue, GPA under chitosan treatment and water control can access the phloem tissue equally, either in terms of the number and duration. Therefore, we suggest that the reduced population growth due to chitosan treatment was related to extra energy consumption during frequent stylet withdrawal and intracellular puncture. This finding indicates the role of chitosan as a plant defense elicitor. However, further investigation regarding this topic is required.

Feeding Behavior of Asian Citrus Psyllid [Diaphorina citri (Hemiptera: Liviidae)] Nymphs and Adults on Common Weeds Occurring in Cultivated Citrus Described Using Electrical Penetration Graph Recordings.

Asian citrus psyllid, Diaphorina citri, transmits Candidatus Liberibacter asiaticus (CLas), the putative causal agent of Huanglongbing disease. Although they primarily feed on the phloem of Citrus and related plants, when grove or host conditions are unfavorable, D. citri may be able to use weed species as alternate food sources for survival. To explore this possibility, electrical penetration graph (EPG) recordings (18 h) were performed to investigate the feeding behavior of psyllid adults and nymphs on three common south Florida weeds (Bidens alba, Eupatorium capillifolium, and Ludwigia octovalvis). EPG recordings revealed that the proportion of time spent by D. citri feeding on xylem was similar on all tested weed species (19%–22%) and on the positive control (20%), the preferred host, Citrus macrophylla. Very little to no phloem feeding was observed on weed species by either nymphs or adults. Histological studies using epifluorescence microscopy showed that salivary sheaths were branched and extended into xylem of weed species, whereas they ended in phloem on citrus plants. No choice behavioral assays showed that adults can obtain some nutrition by feeding on weed species (xylem feeding) and they may be able to survive on them for short intervals, when host conditions are unfavorable.

Barley yellow dwarf virus Can Be Inoculated During Brief Intracellular Punctures in Phloem Cells Before the Sieve Element Continuous Salivation Phase.

The distinguished intracellular stylet puncture called phloem-pd (potential drop [pd]) produced by Myzus persicae has been associated with the transmission of the semipersistently transmitted, phloem-limited Beet yellows virus (BYV, Closterovirus). However, the production of intracellular punctures in phloem cells (phloem-pd) by other aphid species and their role in the transmission of persistently transmitted, phloem-limited viruses are still unknown. Previous studies revealed that inoculation of the persistently transmitted, phloem-limited Barley yellow dwarf virus (BYDV, Luteovirus) is associated mainly with the sieve element continuous salivation phase (E1 waveform). However, the role of brief intracellular punctures that occur before the E1 phase in the inoculation of BYDV by aphids is unknown. We aimed to investigate whether the bird cherry-oat aphid Rhopalosiphum padi (Hemiptera: Aphididae) produced a stereotypical phloem-pd and to study its role in the inoculation of BYDV. The feeding behavior of viruliferous R. padi individuals in barley (Hordeum vulgare) was monitored via the electrical penetration graph (EPG) technique. The feeding process was artificially terminated after the observation of specific EPG waveforms: standard-pds, phloem-pd, and E1. Analysis of the EPG recordings revealed the production of a phloem-pd pattern by R. padi, in addition to a short, distinct E1-like pattern (short-E1), both resulting in successful inoculation of BYDV. Also, the transmission efficiency of BYDV was directly proportional to the time spent by aphids in intracellular salivation in phloem cells. Finally, we discussed the main differences between the inoculation process of semipersistent and persistently transmitted phloem-limited viruses by aphids.

Choice of Tethering Material Influences the Magnitude and Significance of Treatment Effects in Whitefly Electrical Penetration Graph Recordings

The electrical penetration graphing or electropenetrography (EPG) technique is essential for understanding interactions of hemipteran insects with their host plants. Typically, 10–12.5 μm diameter gold wire is used as the tethering material in EPG studies. This wire was originally chosen based on suitability for aphids, but application of the EPG technique to other insects necessitates testing of alternative tethering materials that permit natural foraging and probing behavior. Whiteflies are one group for which EPG studies are increasing, with most researchers using 10 or 12.5 μm diameter gold wire even though these insects are smaller than aphids and very different in mobility. However, 2.5 μm diameter Wollaston process platinum wire has been used for a subset of EPG studies and seems to permit more natural movement and feeding behaviors. Here, we compared EPG variables derived from recordings of the sweet potato whitefly (Bemisia tabaci) tethered with 12.5 μm diameter gold wire or 2.5 μm diameter platinum wire. On a suitable host, gold-tethered whiteflies had reduced phloem phases, which are indicative of host plant acceptance, compared to platinum-tethered whiteflies. When we included a treatment known to reduce plant quality (methyl jasmonate application), platinum-tethered whiteflies exhibited expected reductions in EPG variables related to host acceptance, while gold-tethered whiteflies either had no response, or the opposite response. Our results indicate that tethering material strongly influences the outcome of EPG experiments, with important consequences for evaluations of host plant resistance, putative instances of plant virus manipulation, and feeding variables associated with virus transmission.

Stylet penetration activities of the whitefly Bemisia tabaci associated with inoculation of the crinivirus Tomato chlorosis virus.

Bemisiatabaci is an important vector of numerous plant viruses, including the emergent semi-persistently transmitted crinivirus Tomato chlorosis virus (ToCV). Its vector feeding behaviour is complex, with important implications for virus transmission, epidemiology and control. Thus, the objective of this study was to investigate the role of the stylet penetration activities of B. tabaci in the inoculation of ToCV in tomatoes by using the electrical penetration graph (EPG) technique. EPG recordings were classified into six categories depending on the waveforms observed. The results showed that ToCV inoculation is mainly associated with stylet activities in phloem sieve elements (E1 waveform), as there was a significant increase in the rate of transmission when whiteflies performed waveform E1. The precise stylet activities - either salivation or egestion - associated with virion release, presumably from retention sites in the foregut, need further investigation.

Horticultural mineral oil influences Plum pox virus transmission by Myzus persicae

AbstractThe residual activity of horticultural mineral oil (HMO) on the ability of green peach aphids, Myzus persicae (Sulzer), (GPA) to transmit Plum pox virus (PPV) to peach was measured by infection rates of detached leaves from plants sprayed with either HMO or water as a control that were inoculated using transfer of 25 viruliferous aphids per leaf at 0, 2, 4, 7, 9, 11 and 14 days after treatment (DAT). Persistent effects of HMO residue on the probing and feeding behaviours of GPA were also monitored with the electrical penetration graph (EPG) system. For glasshouse‐grown peach seedlings, the residual activity of HMO reduced PPV infection rates by more than 58% for up to 4 DAT following an initial reduction of approximately 81%. EPG recordings of GPA feeding behaviour showed that HMO significantly delayed first feeding probes and first intracellular punctures by more than 50 min without changing the ensuing stylet penetration behaviour. Applying HMO reduced virus infection rates for up to a week depending on the environmental conditions. EPG monitoring of aphid probing showed that HMO reduced the mean duration and mean number of potential drop (PD) phase feeding occurrences, compared with the water control. A reduction in the PD that has been shown to be related to the transmission of non‐persistently transmitted viruses may partly explain the reduction in PPV infection rates.

Electrical Penetration Graph monitored feeding behavior of cowpea aphid, Aphis craccivora Koch. (Hemiptera:Aphididae), on faba bean, Vicia faba L. (Fabaceae), cultivars

Feeding behavior of cowpea aphid, Aphis craccivora Koch. (Hemiptera: Aphididae), was evaluated on five faba bean, Vicia faba L. (Fabaceae), cultivars, including the resistant cultivar Gazira2, by using the Electrical Penetration Graph (EPG) technique. Experiments were conducted on whole plants (WP) and detached leaves (DL). Fifteen parameters of EPG recording were selected for statistical analysis. Two-way factorial ANOVA showed that the EPG parameter values in WP and DL were significantly different, while the cultivars difference occurred mostly in the WP tissue, as indicated through one-way ANOVA Kruskal-Wallis analysis. Cowpea aphid feeding behavior on WP Gazira2 resistant cultivar had the longest duration of stylet derailment (waveform F) and total probing, but lowest in total duration of pathway (waveform C), xylem ingestion (waveform G),and number of probes. Speculatively, longest duration of waveform F, which had a relation with the mechanical disturbance during feeding, probably is one of the possible resistant factors in Gazira2 cultivar, however this remains intriguing and needs further study.

Electrical Penetration Graph Recording of Russian Wheat Aphid (Hemiptera: Aphididae) Feeding on Aphid-Resistant Wheat and Barley.

Biotypes of Russian wheat aphid, Diuraphis noxia (Kurdjumov), have nullified D. noxia-resistant wheat. In this study, feeding of North American D. noxia was measured in aphids fed resistant and susceptible wheat and barley using electrical penetration graph (EPG) recordings. Interactions between barley genotypes and D. noxia biotypes were significant. EPG recordings of biotype 1 aphids fed on D. noxia-resistant IBRWAGP4-7 barley plants displayed significantly more non-phloem (pathway) phase movements and significantly less sieve element phase (SEP) feeding than on susceptible plants. EPG recordings of D. noxia biotype 2 feeding are the first ever recorded, but no differences between biotype 2-susceptible and -resistant barley plants were found for any EPG parameter in biotype 2 aphids fed barley. No wheat genotype-D. noxia biotype interactions were detected, but when responses were averaged across resistant and susceptible wheat genotypes, biotype 1 displayed a significantly longer pathway phase and significantly more SEP feeding than biotype 2, and biotype 2 engaged in significantly more xylem drinking than biotype 1. IBRWAGP4-7 barley resistance to biotype 1 appears to be controlled by both intercellular factors encountered during the pathway phase and intracellular factors ingested during SEP feeding. The lack of differences in EPG parameters displayed by biotype 2 feeding on barley suggests that biotype 2 resistance in IBRWAGP4-7 barley is based on tolerance to D. noxia feeding instead of altered feeding patterns. Resistance in 'KS94H871' wheat appears to be a function of phloem, non-phloem, and xylem factors that extend the duration of pathway feeding and limit SEP feeding.

Feeding behaviour of a virus‐vector leafhopper on host and non‐host plants characterised by electrical penetration graphs

AbstractMany sap‐feeders are vectors of plant diseases, acquiring and inoculating pathogens at various stages of the feeding process. In oligophagous species, certain aspects of probing behaviour on hosts and non‐hosts may have implications for the range of both pathogens and plants that can be inoculated. We addressed the question of which probing phases (including ingestion) occur on non‐host plants in the case of the common leafhopper Psammotettix alienus (Dahlbom) (Hemiptera: Cicadellidae). This species is a pest on cereals, a vector of the Wheat dwarf virus, and possible carrier of other pathogens. It is regarded as oligophagous on grasses, but has been reported also on other plant families. In a combined electrical penetration graph (EPG) video observation study, we aimed to give a description of the waveforms during the probing process. EPG recordings were made on a suitable host, barley, Hordeum vulgare L. (Poaceae), and on two non‐host plants, the sedge Carex tomentosa L. (Cyperaceae) and the ragweed Ambrosia artemisiifolia L. (Asteraceae). We demonstrated that P. alienus probes on plants other than Poaceae, including dicotyledons. Univariate and multivariate analyses of general probing variables revealed that total and maximal probe durations were shorter and probing progress less advanced on non‐host plants. Waveforms of the pathway phase were stereotypical and statistically not different between the host and non‐host plants. On sedge, the waveform signifying insertion through the plant epidermis was shortened but much more frequent, indicating penetration difficulties and retrials. Most importantly, waveforms indicating phloem ingestion were not present on either of the non‐host plants. Non‐host probing events terminating during the pathway phase suggested that rejection occurred when the stylets were in the mesophyllum. Overall, the EPG signals reflected the unsuitability of A. artemisiifolia and C. tomentosa compared to barley, but the occurrence of probing and the demonstrated level of probing progress imply that pathogen transmission cannot be excluded in the case of many non‐host plants and non‐specific pathogens.

High-throughput phenotyping of plant resistance to aphids by automated video tracking.

BackgroundPiercing-sucking insects are major vectors of plant viruses causing significant yield losses in crops. Functional genomics of plant resistance to these insects would greatly benefit from the availability of high-throughput, quantitative phenotyping methods.ResultsWe have developed an automated video tracking platform that quantifies aphid feeding behaviour on leaf discs to assess the level of plant resistance. Through the analysis of aphid movement, the start and duration of plant penetrations by aphids were estimated. As a case study, video tracking confirmed the near-complete resistance of lettuce cultivar ‘Corbana’ against Nasonovia ribisnigri (Mosely), biotype Nr:0, and revealed quantitative resistance in Arabidopsis accession Co-2 against Myzus persicae (Sulzer). The video tracking platform was benchmarked against Electrical Penetration Graph (EPG) recordings and aphid population development assays. The use of leaf discs instead of intact plants reduced the intensity of the resistance effect in video tracking, but sufficiently replicated experiments resulted in similar conclusions as EPG recordings and aphid population assays. One video tracking platform could screen 100 samples in parallel.ConclusionsAutomated video tracking can be used to screen large plant populations for resistance to aphids and other piercing-sucking insects.Electronic supplementary materialThe online version of this article (doi:10.1186/s13007-015-0044-z) contains supplementary material, which is available to authorized users.

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.

Electrical Penetration Graph Recording (Whitefly)

Electrical penetration graph (EPG) was first developed by Mclean and Kinsey (1964) and later modified by Tjallingii (1978 and 1985). The EPG system turns a phloem-sucking insects and its host plant into part of an electrical circuit that is completed when the insect’s mouthparts penetrate the plant. The electrical signal is amplified by an amplifier and digitized by a converter. Fluctuations in voltage and electrical resistance are recorded and can be matched to specific feeding events. Current protocol is an efficient use of the EPG system to record whitefly feeding behavior on plants.

Modification of Non-Vector Aphid Feeding Behavior on Virus-Infected Host Plant

Virus-infected host plants can have positive, neutral or negative effects on vector aphids. Even though the proportion of non-vector aphids associated with a plant far exceeds that of vector species, little is known about the effect of virus-infected plants on non-vector aphids. In the present study, the English grain aphid Sitobion avenae (Fabricius) (Hemiptera: Aphididae), a non-vector of Wheat dwarf virus (WDV) and Cereal yellow dwarf virus-RPV (CYDV-RPV), was monitored on, virus-infected, virus-free and leafhopper/aphid-infested, and virus- and insect-free (control) barley, Hordeum vulgare L. (Poales: Poaceae), plants. Electrical penetration graph recordings were performed. Compared with the control plants, S. avenae on infected plants exhibited reduced non-probing and pathway phase, and increased phloem sap ingestion phase, and more aphids reached sustained phloem ingestion. However, the electrical penetration graph parameters described above showed no significant differences in aphid feeding behavior on virus-free and vector pre-infested plants and the control barley plants during S. avenae feeding. The results suggest that WDV/CYDV-RPV-infected host plants positively affected the feeding behavior of the non-vector aphid S. avenae. Based on these results, the reasons and trends among the virus-infected host plants' effects on the feeding behavior of non-vector aphids are discussed.