Penetration Graph Recordings Research Articles

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.

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.

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.

Behavioral change of Bemisia tabaci and Trialeurodes vaporariorum (Hemiptera: Aleyrodidae) infected by Lecanicillium muscarium (Hypocreales: Cordycipitaceae)

The effects of entomopathogenic fungus Lecanicillium muscarium on feeding and host preference were investigated on Bemisia tabaci (Gennadius) and Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyroidae) using 2aF43 and Mycotal® strains. Feeding activity was monitored up to day five post fungal inoculation using electric penetration graph while host preference was evaluated by choice-test bioassay for 72 h. Our results showed a reduction in the ability of the infected insects to ingest xylem and reach the phloem. Interestingly the two tested fungal strains interfered on different feeding activities. Only 2aF43 reduced cell puncturing in both insects. Pre-inoculation of plants by 2aF43 increased feeding difficulties and searching time of B. tabaci by 74.9% and 40.1%, respectively. Host choice bioassay showed that insects started aborting the fungal-treated leaf disks after 24 h. By the lapse of 72 h, 2aF43 had a repulsion range of 93.3–95.3% which was higher than that of Mycotal® that ranged between 80.0% and 80.7% in both whiteflies. Using choice-test bioassay and electric penetration graph recording, we revealed that L. muscarium effectively repelled whiteflies and deterred them from normal feeding that potentially reduce plant damage.

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.

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.

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.

Sub-lethal effects of four neonicotinoid seed treatments on the demography and feeding behaviour of the wheat aphid Sitobion avenae

Neonicotinoids are widely used as seed treatments in wheat fields against the grain aphid (Sitobion avenae F.) in China. Due to the degradation of neonicotinoids in wheat plants, wheat aphids are more likely to be exposed to low concentrations of neonicotinoids over long periods. It is therefore expected that neonicotinoids, aside from acute (lethal) effects, may also cause a range of sub-lethal effects on this pest. The growth and fertility of S. avenae feeding on wheat plants treated with a sub-lethal concentration (LC10 ) of imidacloprid, dinotefuran, thiacloprid and thiamethoxam were not greatly affected. However, the population growth parameters of S. avenae were significantly reduced at median lethal concentration (LC50 ). Electronic penetration graph recordings showed a higher percentage of no probing phase and shorter phloem sap ingestion phase on the wheat plants treated with LC10 and LC50 concentrations. The results indicate that even low concentrations of neonicotinoid treatments on wheat seeds have long-term, adverse effects on wheat aphid. As such, neonicotinoid seed treatments have far greater effects on wheat aphids than estimated by acute toxicity tests. These results benefit our understanding on the subtle effects of the four tested neonicotinoids when applied as seed treatments.

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.

Feeding studies on gynoparae, males and apterous virginoparae of Myzus persicae on potato by electrical penetration graph

Abstract: Feeding behaviour of parthenogenetic apterae, post‐teneral gynoparae and males of a holocyclic parthenogenetic lineage of Myzus persicae (Sulzer) (Hem., Aphididae) was studied on potato plants, Solanum tuberosum L. (Solanaceae) by DC‐electrical penetration graph recording. Differences were observed between morphs during the 7‐h recordings, specifically in the first phase of subcuticular probing and in xylem and phloem‐related activities. The time required for the first penetration and first cell puncture of the non‐vascular tissues was shorter in apterae than in gynoparae and males. Apterae more often showed phloem activities and sustained sap ingestion (100%) than winged morphs (ca. 25%). In addition, phloem ingestion was much longer in apterae than in winged morphs, 3458 s and 25–70 s respectively. In contrast, winged morphs spent 14–21% of the available time ingesting sap from xylem while in apterae xylem sap uptake was only for 2% of the time. Furthermore, the data showed that males perform in general all the feeding behaviours that other conspecific morphs exhibit. The differences in feeding behaviour among morphs of M. persicae are discussed in relation to host specialization and to their possible involvement in non‐persistent transmission of viruses.

Stylet activity of cowpea aphid (Homoptera: Aphididae) on leaf extracts of resistant and susceptible cowpea cultivars

Electrical penetration graph recordings using direct current (DC-EPGs) were used to analyze aspects of the probing behavior of cowpea aphid,Aphis craccivora Koch, on intact plants and on hexane, ethyl acetate, and methanol extracts of leaves of aphid-resistant (ICV-12) and aphid-susceptible (ICV-1) cultivars of cowpeaVigna unguiculata (L.) Walp. In one set of experiments, recordings were done on plants with or without parafilm wrapping, or on plants painted with raw leaf juice and extracts of the two cultivars. In another study, recordings were done on leaf extracts homogenized in water or in 0.5M sucrose solution and then placed in parafilm membrane sachets. Electrodes were inserted into soil mix for the experiments on potted plants or into extract fractions and raw juice for the membrane feeding experiments on leaf extracts in parafilm sachets. Waveform signals were recorded from resistance fluctuations from interactions between aphids and substrates, and electromotive forces generated within each preparation. ICV-12 plants with or without parafilm wrapping, and ethyl acetate extracts and raw juice of that cultivar significantly (P≤0.05) reduced stylet penetration behavior. Thus, antixenosis as manifested by disruption of aphid stylet activity on host substrates, appeared to be a governing modality of aphid resistance in ICV-12.

Effects of treatments for electrical penetration graph recordings on behaviour and biology of Aphis craccivora (Aphididae)

Abstract. Two laboratory studies were conducted to investigate effects of treatments for direct “current electrical penetration graph (DC‐EPG) recordings or ‘tether effect’, on behaviour and reproductive performance of cowpea aphid Aphis craccivora Koch. The experiments constituted a control study in application of DC‐EPGs to analyse cowpea aphid feeding behaviour and host plant resistance mechanisms. Resistant (ICV‐12) and susceptible (ICV‐1) cultivars of cowpea Vigna unguiculata (L.) Walp were used. EPG treatments included two groups of aphids: tethered aphids that were exposed to DC electricity via an attachment of a thin, flexible gold wire on their dorsum using a droplet of adhesive silver paint, and ‘free’ (untethered) aphids with a dorsal spot of silver paint only. EPGs of the tethered aphids were recorded continuously for c.! h, whereas from the ‘free’ aphids recordings were done only for brief periods of 2–5 min, by temporarily contacting a gold wire to the spot of silver paint. Waveform signals generated from resistance fluctuations and electromotive forces, and representing aphid stylet penetration behaviour were recorded. A separate experiment was conducted to investigate effects of EPG treatments on aphid survivorship and population growth. Overall, EPG treatments did not significantly affect aphid stylet penetration behaviour or life‐table parameters. However, effects of crop cultivar on those characteristics were significant. Waveform E2, which denotes aphid ingestion in phloem sieve elements, and non‐penetration behaviour were important indicators of aphid resistance in ICV‐12. Also, apart from the number of aphid generations, other life‐table parameters were useful indicators of ICV‐12 resistance. Thus, DC‐EPGs provided a reliable technique for studying aphid stylet behaviour, and investigation of aphid resistance in cowpeas.