Introduction The potato psyllid Bactericera cockerelli is the insect vector of the fastidious bacterium ‘ Candidatus Liberibacter solanacearum’. The bacterium infects both B. cockerelli and plant species, causing zebra chip (ZC) disease of potato and vein-greening disease of tomato. Temperatures are known to influence the initiation and progression of disease symptom in the host plant, and seasonal transitions from moderate to high temperatures trigger psyllid dispersal migration to facilitate survival. Methods ‘ Ca . L. solanacearum’ -infected and uninfected psyllids were reared at previously established ‘permissible’, optimal, and ‘non-permissible’ and temperatures of 18°C, 24°C, and 30°C, respectively. Gene expression profiles for ‘Ca. L. solanacearum’-infected and -uninfected adult psyllids reared at different temperatures were characterized by Illumina RNA-Seq analysis. Bacterial genome copy number was quantified by real-time quantitative-PCR (qPCR) amplification. Results Relative gene expression profiles varied in psyllids reared at the three experimental temperatures. Psyllids reared at 18°C and 30°C exhibited greater fold-change increased expression of stress- and ‘ Ca . L. solanacearum’ invasion-related proteins. Quantification by qPCR of bacterial genome copy number revealed that ‘ Ca . L. solanacearum’ accumulation was significantly lower in psyllids reared at 18°C and 30°C, compared to 24°C. Discussion Temperature is a key factor in the life history of potato psyllid and multiplication/accumulation of ‘ Ca . L. solanacearum’ in both the plant and psyllid host, influences the expression of genes associated with thermal stress tolerance, among others, and may have been instrumental in driving the co-evolution of the pathosystem.

Abstract Understanding host use by psyllids (Hemiptera: Psylloidea) benefits from comparative studies of behavior on host and nonhost plant species. While most psyllid species develop on one or a few closely related plant species, some species are generalized enough to develop on species across plant families. We used electropenetography (EPG) technology to compare probing activities of an oligophagous psyllid (Bactericera cockerelli (Šulc)) and a host-specialized psyllid (Bactericera maculipennis) on two species of Solanaceae (potato, Solanum tuberosum L. and matrimony vine, Lycium barbarum L.) and two species of Convolvulaceae (field bindweed, Convolvulus arvensis L. and sweet potato, Ipomoea batatas). Bactericera cockerelli develops on all four species, albeit with longer development times on Convolvulaceae. Bactericera maculipennis develops only on Convolvulaceae. Bactericera cockerelli fed readily from phloem of all four species, but the likelihood of entering phloem and duration of time in phloem was reduced on suboptimal hosts (Convolvulaceae) relative to behavior on Solanaceae. We observed instances of cycling between bouts of phloem salivation and ingestion in assays of optimal (Solanaceae) hosts not observed on Convolvulaceae. The Convolvulaceae-specialized B. maculipennis (Crawford) failed to feed from phloem of nonhosts (Solanaceae). Both psyllid species readily ingested from xylem of all plant species, irrespective of host status. Our finding that phloem feeding by B. maculipennis did not occur on potato has implications for understanding epidemiology of phloem-limited psyllid-vectored plant pathogens. Our results also showed that EPG assays detect subtle variation in probing activities that assist in understanding host use by psyllids.

Understanding factors that affect the population dynamics of insect pest species is key for developing integrated pest management strategies in agroecosystems. Most insect pest populations are strongly regulated by abiotic factors such as temperature and precipitation, and assessing relationships between abiotic conditions and pest dynamics can aid decision-making. However, many pests are also managed with insecticides, which can confound relationships between abiotic factors and pest dynamics. Here we used data from a regional monitoring network in the Pacific Northwest United States to explore effects of abiotic factors on populations of an intensively managed potato pest, the potato psyllid (Bactericera cockerelli Šulc), which can vector Candidatus Liberibacter psyllaurus, a bacterial pathogen of potatoes. We assessed effects of temperature on psyllid populations, and show psyllid population growth followed predictable patterns within each year, but there was considerable variation across years in psyllid abundance. Examination of seasonal weather patterns suggested that in 2017, when psyllid populations were less abundant by several orders of magnitude than other years, a particularly long and cold period of winter weather may have harmed overwintering populations and limited population growth. The rate of degree-day accumulation over time, as well as total degree-day accumulation also affected trap catch abundance, likely by mediating the number of psyllid generations per season. Our findings indicate that growers can reliably infer the potential magnitude of risk from potato psyllids using monitoring data, date of first detection, seasonal weather patterns, and population size early in the growing season.

Zebra chip (ZC) disease of potato (Solanum tuberosum) is associated with infection by 'Candidatus Liberibacter solanacearum' (Lso). Two haplotypes of Lso-A and B-occur in the United States. Lso haplotype B is more virulent than haplotype A, causing greater disease incidence in tubers, more severe symptoms, and greater loss in tuber yield. This study assessed whether tubers from infected plants generate new infected plants the following year. The effects of both Lso haplotypes A and B on tuber resprout were examined on five potato cultivars. When compared with noninfected tubers, overall plant emergence rate from Lso A- or B-infected tubers was lower, plants emerged slower, and plants generated lower daughter tuber yields in weight and quantity. Plants generally emerged poorly from Lso B-infected tubers and produced lower daughter tuber yields than Lso A-infected tubers. Regardless of Lso treatment, all daughter tubers were asymptomatic, and only 0.3% tested positive for Lso in experiments conducted over 2 years. This suggests that plants generated from Lso A- and Lso B-infected seed potatoes with severe ZC symptoms are likely not a significant source of Lso in potato fields.

Near-Infrared (NIR) spectroscopy (900-2600 nm) was evaluated as a rapid, non-destructive method for detection of zebra chip disease (ZC) in potatoes. Two models were tested; one that directly correlated spectra with ZC and one that measured sugar concentrations which in turn are known to be correlated with ZC. Applying stepwise regression in conjunction with canonical discriminant analysis to raw spectra, total classification accuracy of 98.35% was achieved in discriminating infected potatoes from control, with 2% false negative and 1% false positive error rates. The same analysis applied to 2nd derivative spectra yielded 97.25% accuracy with equal false negative and false positive error rates. Canonical discriminant analysis applied to sucrose, glucose, and fructose concentrations previously determined by high-performance liquid chromatography yielded 96.7% classification accuracy, with 4.3% false positive and 2.3% false negative rates. Accuracy did not significantly differ when fructose was excluded from the model. Partial least squares regression models built to predict sugar concentrations from the 2nd derivative NIR spectra resulted in R-2 for actual vs. predicted concentrations of 0.7 and 0.72 respectively for sucrose and glucose, 0.63 for fructose, and 0.81 for total sugars. Given the relatively low R-2 values in measuring sugar concentrations directly from the spectra it was concluded that classification accuracy is highest for models that directly correlate spectral features to ZC without considering sugar concentrations. Furthermore, this indicates that although NIR can detect infection, it may not be effective for evaluating severity of ZC in fresh potatoes. Published by Elsevier Ltd on behalf of IAgrE.

Two haplotypes of the pathogen, ‘Candidatus Liberibacter solanacearum,’ (Lso) and four haplotypes of the insect vector, Bactericera cockerelli, are associated with zebra chip disease of potato. Whether disease severity or incidence is influenced by pathogen or insect haplotype is poorly understood. The role of Lso ‘A’ and ‘B,’ transmitted by three haplotypes of B. cockerelli, on disease severity and incidence in eight potato cultivars was analyzed. Both haplotypes of Lso induced tuber symptoms. In general, Lso B caused higher incidence of symptoms, and greater reduction in tubers compared with Lso A. Lso B was associated with more severe tuber symptoms, producing fewer mild or moderate tuber symptoms. Lso A was associated with less severe tuber symptoms, despite being able to induce severe symptoms. Disease incidence, tuber yield, and symptom severity ratings were not dependent upon the psyllid haplotype transmitting the pathogen, suggesting that pathogen, not insect haplotype affects Lso transmission.

Potato psyllid, Bactericera cockerelli (Šulc), causes economic damage to potato crops throughout the major potato growing regions of western North America. When cultivated crops are not available, potato psyllid often occurs on non-crop hosts. In the southern U.S. and northern Mexico, native species of Lycium (Solanaceae) are important non-crop hosts for the psyllid. We determined whether Old World species of Lycium now widespread in the Pacific Northwest are reservoirs of potato psyllid in this growing region. We examined Lycium spp. across a wide geographic region in Washington, Oregon, and Idaho at irregular intervals during three growing seasons. Potato psyllids were present at all locations. To determine whether Lycium is also a host during intervals of the year in which the potato crop is not available, we monitored a subset of these sites over the entire year. Six sites were monitored at 1- to 3-week intervals from June 2014 to June 2016. Psyllids were present on Lycium throughout the year at all sites, including during winter, indicating that Lycium is also a host when the potato crop is seasonally not available. Psyllid populations included a mixture of Northwestern and Western haplotypes. We observed well-defined spring and fall peaks in adult numbers, with peaks separated by long intervals in which psyllid numbers were very low. Seasonal patterns in psyllid numbers on these non-native Lycium hosts were very similar to what has been observed on native Lycium in the desert southwest region of the U.S. Our findings demonstrate that potato psyllid associates with Lycium across a broad geographic region within the Pacific Northwest. These results will assist in predicting sources of potato psyllid colonizing potatoes in this important growing region.

HomePlant DiseaseVol. 101, No. 6First Report of Beet Leafhopper Transmitted Virescence Agent Phytoplasma in Capsicum annuum and Circulifer tenellus in Mexico PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Beet Leafhopper Transmitted Virescence Agent Phytoplasma in Capsicum annuum and Circulifer tenellus in MexicoK. D. Swisher, J. E. Munyaneza, R. Velásquez-Valle, and J. Mena-CovarrubiasK. D. SwisherSearch for more papers by this author, J. E. MunyanezaSearch for more papers by this author, R. Velásquez-ValleSearch for more papers by this author, and J. Mena-CovarrubiasSearch for more papers by this authorAffiliationsAuthors and Affiliations K. D. Swisher J. E. Munyaneza , United States Department of Agriculture, Agricultural Research Service, Temperate Tree Fruit and Vegetable Research Unit, Wapato, WA 98951 R. Velásquez-Valle J. Mena-Covarrubias , Campo Experimental Zacatecas, INIFAP, Calera de V. R., Zacatecas, C.P. 98500, Mexico. Published Online:16 Mar 2017https://doi.org/10.1094/PDIS-12-16-1723-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Chili pepper (Capsicum annuum L.) plants in Durango and Zacatecas, Mexico, in September and October 2014, had small, chlorotic, curled leaves, plant stunting, and/or big bud symptoms characteristic of phytoplasma infection (Lee et al. 2004). Symptomatic pepper plants were found in fields ranging from 6 to 10 ha at an incidence of 5 to 15% near Poanas, Durango (33 sampled); Sombrerete, Zacatecas (seven sampled); Villa de Cos, Zacatecas (33 sampled); Laguna Seca, Zacatecas (40 sampled); and Calera, Zacatecas (41 sampled). Total DNA was extracted from foliar tissue with the CTAB extraction method (Munyaneza et al. 2010), and tested using universal phytoplasma nested PCR with primers P1/P7 and FU5/RU3 (Crosslin et al. 2006). Of 156 samples, 104 (67%) were positive for phytoplasma, including three from Poanas, seven from Sombrerete, 27 from Villa de Cos, 31 from Laguna Seca, and 36 from Calera. All positive samples were tested for beet leafhopper transmitted virescence agent (BLTVA) phytoplasma of the clover proliferation group 16SrVI, subgroup A, using nested PCR with primers P1/P7 and BLTVA-specific FU5/BLTVA-int (Crosslin et al. 2006); all were positive for BLTVA. DNA was extracted from BLTVA beet leafhopper vectors, Circulifer tenellus (Baker), collected from pepper fields and weeds near pepper fields in Zacatecas, Mexico, in September and October 2014, using the CTAB method (Crosslin et al. 2006) and tested for BLTVA using nested PCR with primers P1/P7 and FU5/BLTVA-int. Of 52 insect samples, 23 (44%) were positive for BLTVA. Sequence analysis of the FU5-BLTVA-int amplicon from six pepper plants (two each) from Poanas, Durango; Sombrerete, Zacatecas; and Laguna Seca, Zacatecas; and three C. tenellus samples from Zacatecas, produced a consensus sequence from each host (base pairs 224 to 1,415, GenBank accession KY047614 and KY047615, respectively). BLAST analysis of this region of 16S rRNA gene was 100% identical to Columbia Basin purple top phytoplasma (known as BLTVA) (Crosslin et al. 2006), from the 16SrVI Clover proliferation group (KR072666.1). To verify phytoplasma infection, six plants and three insect samples were subjected to PCR using universal phytoplasma nested primers P1/P7 and R16F2n/R16R2 (Lee et al. 2004), and the amplicons were sequenced. A consensus sequence resulted from both the plant and insect samples (base pairs 1 to 1,250, KY047614 and KY047615, respectively). In silico restriction fragment length polymorphism analysis was done using iPhyClassifier analysis tool (Zhao et al. 2009). Both sequences were identified as 16Sr group VI, subgroup A, showing 99.7% similarity with ‘Candidatus Phytoplasma trifolii’ (AY390261). ‘Ca. Phytoplasma trifolii’ was reported in peppers in Mexico (Mauricio-Castillo et al. 2015), but the specific strain of 16SrVI-A group was not determined. Therefore, this is the first report of the clover proliferation group strain BLTVA phytoplasma in peppers and its insect vector in this region of Mexico. BLTVA is an economically important pathogen in solanaceous crops in the U.S. (Lee et al. 2004), and poses a threat to the pepper-growing region in Mexico, highlighting the need for control of the beet leafhopper vector of BLTVA phytoplasma.References:Crosslin, J. M., et al. 2006. Plant Dis. 90:663. https://doi.org/10.1094/PD-90-0663 Link, ISI, Google ScholarLee, I.-M., et al. 2004. Plant Dis. 88:429. Abstract, Google ScholarMauricio-Castillo, J. A., et al. 2015. Rev. Fitotec. Mex. 38:389. ISI, Google ScholarMunyaneza, J. E., et al. 2010. J. Econ. Ent. 103:1060. https://doi.org/10.1603/EC10027 Crossref, ISI, Google ScholarZhao, Y., et al. 2009. Int. J. Syst. Evol. Microbiol. 59:2582. https://doi.org/10.1099/ijs.0.010249-0 Crossref, ISI, Google ScholarDetailsFiguresLiterature CitedRelated Vol. 101, No. 6 June 2017SubscribeISSN:0191-2917e-ISSN:1943-7692 Metrics Article History Issue Date: 17 May 2017Published: 16 Mar 2017First Look: 7 Feb 2017Accepted: 25 Jan 2017 Pages: 1032-1032 InformationThis article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2017.Cited byCandidatus Phytoplasma trifolii (clover proliferation phytoplasma)CABI Compendium, Vol. CABI CompendiumDetection of Pathogens Associated with Psyllids and Leafhoppers in Capsicum annuum L. in the Mexican States of Durango, Zacatecas, and MichoacánK. D. Swisher, J. E. Munyaneza, R. Velásquez-Valle, and J. Mena-Covarrubias23 October 2017 | Plant Disease, Vol. 102, No. 1Phytoplasmas Infecting Vegetable, Pulse and Oil Crops5 September 2018

The Nearctic psyllid Bactericera maculipennis (Crawford) (Hemiptera: Psylloidea: Triozidae) is one of only five known species of Psylloidea worldwide whose host plants include species of Convolvulaceae (Solanales). Current checklists of North American Psylloidea report B. maculipennis only from California and Utah. Our surveys of field bindweed, Convolvulus arvensis L. (Convolvulaceae), an OldWorld plant introduced into North America, show that B. maculipennis is considerably more widespread than indicated by historical accounts. We update the psyllid's geographic range to include four states (Washington, Idaho, Oregon, Montana) not previously included in contemporary checklists. The egg and fifth instar nymph are described. We provide characters of the egg and nymph that distinguish this species from a congeneric species, Bactericera cockerelli (Sulc), occasionally found on field bindweed. Photographs of the male and female terminalia are provided. Bactericera maculipennis developed successfully on field bindweed and on several species of Ipomoea (Convolvulaceae) in laboratory assays. Overwintering females collected from leaf litter and dead or dormant stems of C. arvensis at locations in Central Washington mated and began to oviposit within 7 days of removal from the field, suggesting that B. maculipennis overwinters in a temperature-controlled quiescence rather than in a true reproductive diapause. Eggs and nymphs of B. maculipennis were found on stems of C. arvensis well into November in Central Washington, suggesting that this psyllid also may overwinter in pre-adult stages, as indicated by literature accounts from the 1940s and 1950s. Lastly, we propose that successful colonization of the invasive and exotic weed C. arvensis by B. maculipennis has allowed the psyllid to expand its geographic range well beyond historical boundaries. This conclusion is based upon the scarcity of native Convolvulaceae within regions in which the psyllid is newly recorded, combined with the now extensive distribution of the invasive C. arvensis in North America.

Candidatus Liberibacter solanacearum' (Lso) is a phloem-limited bacterium that severely affects important Solanaceae and Apiaceae crops, including potato, tomato, pepper, tobacco, carrot and celery. This bacterium is transmitted to solanaceous species by potato psyllid, Bactericera cockerelli, and to Apiaceae by carrot psyllids, including Trioza apicalis and Bactericera trigonica. Five haplotypes of Lso have so far been described, two are associated with solanaceous species and potato psyllids, whereas the other three are associated with carrot and celery crops and carrot psyllids. Little is known about cross-transmission of Lso to carrot by potato psyllids or to potato by carrot psyllids. Thus, the present study assessed whether potato psyllid can transmit Lso to carrot and whether Lso haplotypes infecting solanaceous species can also infect carrot and lead to disease symptom development. In addition, the stylet probing behavior of potato psyllid on carrot was assessed using electropenetrography (EPG) technology to further elucidate potential Lso transmission to Apiaceae by this potato insect pest. Results showed that, while potato psyllids survived on carrot for several weeks when confined on the plants under controlled laboratory and field conditions, the insects generally failed to infect carrot plants with Lso. Only three of the 200 carrot plants assayed became infected with Lso and developed characteristic disease symptoms. Lso infection in the symptomatic carrot plants was confirmed by polymerase chain reaction assay and Lso in the carrots was determined to be of the haplotype B, which is associated with solanaceous species. EPG results further revealed that potato psyllids readily feed on carrot xylem but rarely probe into the phloem tissue, explaining why little to no Lso infection occurred during the controlled laboratory and field cage transmission trials. Results of our laboratory and field transmission studies, combined with our EPG results, suggest that the risk of Lso infection and spread between psyllid-infested solanaceous and Apiaceae crops is likely to be negligible under normal field conditions.

In 2014, carrot plants in Zacatecas, Mexico, were found with yellow, brown, or purple-colored leaves, which were occasionally smaller and rolled. Roots of these affected plants were hairy, deformed, and small. Molecular diagnostics failed to detect phytoplasmas in these samples, but identified Spiroplasma citri in 58 and 94% of the samples using PCR targeting the spiralin and adhesion-related protein 1 (arp1) genes, respectively. Sequence analysis confirmed the presence of S. citri, and identified a novel, putative arp gene in one carrot sample. S. citri is a phytopathogenic mollicute transmitted by leafhopper species. Beet leafhoppers (Circulifer tenellus Baker) collected in the same state of Zacatecas, Mexico, were subsequently tested for S. citri infection, and 36.5% were positive using PCR targeting the arp1 gene. Sequencing analysis confirmed the presence of S. citri in the leafhoppers. This is the first report of S. citri in carrot and C. tenellus in Mexico. Previously in the Americas, S. citri in carrot was only reported in Washington and California in the United States. The presence of S. citri in carrots and the beet leafhopper in Mexico, suggests that this pathogen could become a threat to vegetable industries in this region of Mexico, including the carrot industry.

The psyllid Bactericera maculipennis (Crawford) (Hemiptera: Triozidae) often cohabits field bindweed (Convolvulus arvensis, Solanales: Convolvulaceae) and other plants with the congeneric psyllid, Bactericera cockerelli (Šulc), in the Pacific Northwestern United States. Bactericera cockerelli is a vector of "Candidatus Liberibacter solanacearum," the pathogen associated with zebra chip disease of potato (Solanales: Solanaceae). Because B. maculipennis and B. cockerelli both naturally occur on certain plants, we surveyed B. maculipennis adults collected from Washington and Idaho for presence of "Ca. L. solanacearum" to determine whether this psyllid also harbors this pathogen. Liberibacter was present in 30% of field-collected B. maculipennis and in 100% of colony-reared psyllids. Sequences of 16S rDNA and microsatellite markers revealed that "Ca. L. solanacearum" from B. maculipennis was closely related to Liberibacter haplotype B from B. cockerelli. Results of laboratory assays demonstrated that Liberibacter can be transmitted between B. cockerelli and B. maculipennis on plants within the Convolvulaceae. Potato plants challenged with Liberibacter-infected B. maculipennis did not become infected, apparently because potato is not a suitable host for the psyllid. We therefore conclude that B. maculipennis is not a direct threat to potato production, despite its association with Liberibacter. We are the first to report that "Ca. L. solanacearum" is associated with a psyllid other than B. cockerelli in North America. Results of our study demonstrate the importance of understanding the complete ecology of psyllids-including interactions with other psyllids on non-crop hosts-in predicting what crops or regions are potentially susceptible to the spread of Liberibacter.

Potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae), is an economic pest of solanaceous crops in North and Central America, and in New Zealand. Four genetic haplotypes of the psyllid have been identified in North America. Three of these haplotypes (Central, Western, and Northwestern) are common on potato crops within the major potato-growing regions of Idaho, Oregon, and Washington. Within this growing region, a weedy perennial nightshade, Solanum dulcamara (bittersweet nightshade), has been identified to be an important overwintering host and spring or summer source of psyllids colonizing potato fields. It is unclear whether bittersweet nightshade is a highly suitable host plant for all three haplotypes known to occur in the Pacific Northwest. The objective of the present study was to examine developmental traits and adult body size of all three haplotypes of psyllids reared on potato and bittersweet nightshade. Averaged over haplotype, development times were longer for psyllids reared on nightshade than potato. Duration of the preoviposition period, egg incubation requirements, nymphal development time, and total developmental time averaged 7.4, 5.9, 23.5, and 29.5 d on nightshade and 4.9, 5.5, 22.3, and 27.9 d on potato, respectively. The largest host effects were found for the Central haplotype, which exhibited a substantially extended (by over 5 d) preoviposition period on nightshade compared with potato. Averaged over host plant, nymphal and total development times of the Northwestern haplotype were longer (25.5 and 31.1 d, respectively) than those of the Western and Central haplotypes. The Northwestern haplotype was largest in overall body size, while the Central haplotype had the smallest overall body size, irrespective of host plant. Both sexes exhibited this trend.

Potato psyllid, Bactericera cockerelli (Sulc), is a seasonal insect pest in the Lower Rio Grande Valley of Texas, where it transmits the bacterial pathogen "Candidatus Liberibacter solanacearum" that causes zebra chip disease of potato. Studies were conducted to evaluate host preference of B. cockerelli adults for different plant species, and plant size and density. Settling and oviposition behavior of B. cockerelli was studied on its wild and cultivated solanaceous hosts, including potato, tomato, pepper, eggplant, and silverleaf nightshade, under both field and laboratory conditions. Naturally occurring B. cockerelli were used to evaluate host preference under open field conditions throughout the growing season. Settling and oviposition preference studies in the laboratory were conducted as cage-release experiments using pairs of plants, and observations were recorded over a 72-h period. Results of field trials indicated that naturally occurring B. cockerelli preferred potato and tomato equally for settling and oviposition, but settled on pepper, eggplant, and silverleaf nightshade only in the absence of potato and tomato. Under laboratory conditions, B. cockerelli adults preferred larger host plants, regardless of the species tested. Results also showed that movement of B. cockerelli was minimal after initial landing and settling behavior was influenced by host plant density. Lone plants attracted the most psyllids and can be used as sentinel plants to monitor B. cockerelli activity. Information from both field and laboratory studies demonstrated that not only host plant species determined host selection behavior of B. cockerelli adults, but also plant size and density.

We examined the effects of photoperiod on reproductive diapause of three haplotypes of potato psyllid, Bactericera cockerelli (Hemiptera: Triozidae), collected from three geographic locations: south Texas (Central haplotype), California (Western haplotype), and Washington State (Northwestern haplotype). Psyllids were reared from egg hatch to adult eclosion under short- and long-day conditions, to determine whether short-days led to a lack of mating, delays in ovarian development, and accumulation of fat by female psyllids. Our expectation was that a reproductive response to short-days would be more likely to be exhibited by psyllids of the northern-latitude haplotype (Northwestern) than psyllids of the other two haplotypes. We also examined whether this species exhibited a photoperiod-controlled polymorphism in body size, as observed in other psyllid species, by comparing six body and wing measures of psyllids reared under short- and long-day conditions. Virtually 100% of females of each haplotype exhibited both egg maturation and mating at both long- and short-day conditions, providing no evidence that this species exhibits a photoperiod-induced reproductive diapause. Fat was present in most psyllids, although with higher probability of presence in short-day females than long-day females. Phortoperiod had no effect on body size. We found differences among haplotypes in body size, with psyllids from Washington State (Northwestern haplotype) having larger wings and longer tibiae than psyllids of the two southern populations. Our photoperiod results, combined with overwintering observations for this species and for other Triozidae, prompted us to hypothesize that potato psyllid -- at least in the Pacific Northwest growing region -- overwinters in a temperature-controlled quiescence rather than in a true diapause.

Zebra chip (ZC), a new and economically important disease of potato in the United States, Mexico, Central America, and New Zealand, is caused by the bacterium "Candidatus Liberibacter solanacearum", transmitted to potato by the potato psyllid, Bactericera cockerelli. The disease has caused millions of dollars in losses to the potato industry. Whole crops have been rejected because of ZC, occasionally leading to abandonment of entire fields. Plant growth and yield are severely affected by the disease. Chips or fries processed from ZC-infected tubers exhibit dark stripes that become markedly more visible with frying, and hence are commercially unacceptable. Additionally, the disease causes serious losses to the fresh market, tablestock and export potato industry. ZC-infected tubers generally do not sprout and if they do, produce hair sprouts, weak, or short-lived plants. Furthermore, there are indications that ZC symptoms might develop in tubers during storage. All commercial potato cultivars are susceptible to ZC, thus management tactics targeted against the potato psyllid are currently the only means to effectively manage the disease. An overview of ZC history, geographic distribution, biology, epidemiology, and management are discussed.

The potato psyllid, Bactericera cockerelli (Šulc) (Hemiptera: Triozidae), is a vector of the phloem-limited bacterium ‘Candidatus Liberibacter solanacearum’ (Lso), the putative causal agent of zebra chip disease of potato. Little is known about how potato psyllid transmits Lso to potato. We used electrical penetration graph (EPG) technology to compare stylet probing behaviors and efficiency of Lso transmission of three haplotypes of potato psyllid (Central, Western, Northwestern). All haplotypes exhibited the full suite of stylet behaviors identified in previous studies with this psyllid, including intercellular penetration and secretion of the stylet pathway, xylem ingestion, and phloem activities, the latter comprising salivation and ingestion. The three haplotypes exhibited similar frequency and duration of probing behaviors, with the exception of salivation into phloem, which was of higher duration by psyllids of the Western haplotype. We manipulated how long psyllids were allowed access to potato (“inoculation access period”, or IAP) to examine the relationship between phloem activities and Lso transmission. Between 25 and 30% of psyllids reached and salivated into phloem at an IAP of 1 hr, increasing to almost 80% of psyllids as IAP was increased to 24 h. Probability of Lso-transmission was lower across all IAP levels than probability of phloem salivation, indicating that a percentage of infected psyllids which salivated into the phloem failed to transmit Lso. Logistic regression showed that probability of transmission increased as a function of time spent salivating into the phloem; transmission occurred as quickly as 5 min following onset of salivation. A small percentage of infected psyllids showed extremely long salivation events but nonetheless failed to transmit Lso, for unknown reasons. Information from these studies increases our understanding of Lso transmission by potato psyllid, and demonstrates the value of EPG technology in exploring questions of vector efficiency.

Zebra chip (ZC), an economically important disease of potato, is caused by 'Candidatus Liberibacter solanacearum' (Lso) transmitted by the potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae). Currently, using insecticides against potato psyllid is the only means to manage ZC. However, the ability of the potato psyllid to rapidly transmit Lso represents a substantial challenge in preventing the spread of ZC. Cyantraniliprole, a novel second-generation anthranilic diamide insecticide has been shown to deter insect feeding and reduce disease transmission. During this study, the effect of cyantraniliprole on potato psyllid probing behavior was assessed using electrical penetration graph technology and compared with abamectin, a commonly used insecticide to control potato psyllid. Results showed that both cyantraniliprole and abamectin significantly deterred probing behavior of the potato psyllid. Average duration of intercellular stylet penetration on cyantraniliprole- and abamectin-treated and untreated control plants was 2.36, 1.80, and 9.15 h, respectively. It took psyllids 1.82, 1.10, and 2.42 h to reach the xylem of cyantraniliprole- and abamectin-treated and untreated plants, respectively. Xylem sap ingestion duration averaged 0.53, 0.57, and 3.66 h on cyantraniliprole- and abamectin-treated and untreated controls, respectively. None of the psyllids exposed to insecticide-treated plants reached the phloem tissue, except one that bypassed the xylem. The insects completely ceased probing after 4.44 and 3.64 h on cyantraniliprole- and abamectin-treated plants, respectively, in contrast with those on untreated plants that probed throughout the entire 24-h experiment duration. These results indicate that cyantraniliprole is as effective as abamectin in deterring potato psyllid feeding and could significantly reduce transmission of Lso and the spread of ZC.

The potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae) is a small phloem-feeding insect that develops almost exclusively on plants within the Solanaceae (Fig. 1A). The psyllid was described in 1909 by Karel Sulc from specimens collected in Boulder, Colorado, and is found in Mexico, Central America, the western U.S., and southern Canada, and as an introduction in New Zealand (Wallis 1955, Teulon et al. 2009, Munyaneza 2012). Outbreaks of potato psyllid in North America occurred at regular intervals in potatoes, tomatoes, and peppers beginning in the late 1800s and extending into the mid-1900s, largely along a corridor on both sides of the Rocky Mountains. The outbreaks failed to extend into the Pacific Northwest. That pattern changed dramatically in 2011, when an outbreak of potato psyllid caused massive economic losses to potato growers in Washington, Oregon, and Idaho. Losses were due to a new tuber disorder (“zebra chip”; Fig. 1 B-C), now known to be associated with a bacterium that is vectored by potato psyllid. Fig. 1. (A) Adult potato psyllid. (B, C) Discoloration of infected fresh tubers and of tuber slices after frying. The historical absence of psyllid problems in the Pacific Northwest means that our understanding of psyllid biology under Pacific Northwest conditions is woefully lacking. The outbreak in 2011, coupled with our limited …