Bactericera Cockerelli Research Articles

Effects of ‘Candidatus Liberibacter Solanacearum’ Haplotype on Atlantic Potato Tuber Emergence Rate in South Texas

The bacterium ‘Candidatus Liberibacter solanacearum’ (Lso) is a phloem-restricted plant pathogen associated with different diseases worldwide. In North America, two haplotypes, LsoA and LsoB, are vectored by the potato psyllid, Bactericera cockerelli Sulc that causes zebra chip (ZC) in potato (Solanum tuberosum L.) and other solanaceous plants. In potato, both haplotypes cause similar symptoms albeit with different severities: LsoB-infected potato plants exhibit more severe ZC tuber symptoms compared to LsoA-infected plants. Previous research suggested that Lso-infected plants could produce viable seed tubers, potentially creating a reservoir for Lso propagation. The current study evaluated the effect of Lso haplotype on the emergence rate of tubers produced by infected potato plants (var. ‘Atlantic’) grown in the Lower Rio Grande area during the 2018 and 2019 growing seasons. Five Lso treatments were evaluated: uninfested controls, plants infested with uninfected psyllids (LsoFree), plants infested with LsoA- or LsoB-infected psyllids (LsoA and LsoB, respectively), and plants infested with psyllids co-infected with both Lso haplotypes (LsoAB). A portion of harvested tubers were evaluated for ZC symptom severity using a visual score. The remaining tubers were placed in cold storage for six months and then used as seed tubers to compare emergence and plant development rates among the treatments. This study confirms the previously reported differences in ZC symptom severity between Lso haplotypes. Furthermore, this study showed that tubers produced by Lso-infected plants were 90.1 ± 8.2% inviable. Importantly, all plants developing from these seed tubers tested negative for the presence of Lso. The results of this study suggest that while seed tubers produced by Lso-infected plants can germinate, the daughter plant was not infected by Lso. Therefore, Atlantic tubers produced by previously infected plants with Lso haplotypes A and B in South Texas do not represent a reservoir for Lso disease.

Acquisition and transmission of two \u2018Candidatus Liberibacter solanacearum\u2019 haplotypes by the tomato psyllid Bactericera cockerelli

‘Candidatus Liberibacter solanacearum’ (Lso) is a pathogen of solanaceous crops. Two haplotypes of Lso (LsoA and LsoB) are present in North America; both are transmitted by the tomato psyllid, Bactericera cockerelli (Šulc), in a circulative and propagative manner and cause damaging plant diseases (e.g. Zebra chip in potatoes). In this study, we investigated the acquisition and transmission of LsoA or LsoB by the tomato psyllid. We quantified the titer of Lso haplotype A and B in adult psyllid guts after several acquisition access periods (AAPs). We also performed sequential inoculation of tomato plants by adult psyllids following a 7-day AAP and compared the transmission of each Lso haplotype. The results indicated that LsoB population increased faster in the psyllid gut than LsoA. Further, LsoB population plateaued after 12 days, while LsoA population increased slowly during the 16 day-period evaluated. Additionally, LsoB had a shorter latent period and higher transmission rate than LsoA following a 7 day-AAP: LsoB was first transmitted by the adult psyllids between 17 and 21 days following the beginning of the AAP, while LsoA was first transmitted between 21 and 25 days after the beginning of the AAP. Overall, our data suggest that the two Lso haplotypes have distinct acquisition and transmission rates. The information provided in this study will improve our understanding of the biology of Lso acquisition and transmission as well as its relationship with the tomato psyllid at the gut interface.

The ability of the green peach aphid (Myzus persicae) to penetrate mesh crop covers used to protect potato crops against tomato potato psyllid (Bactericera cockerelli).

In Central and North America, Australia and New Zealand, potato (Solanum tuberosum) crops are attacked by Bactericera cockerelli, the tomato potato psyllid (TPP). ‘Mesh crop covers’ which are used in Europe and Israel to protect crops from insect pests, have been used experimentally in New Zealand for TPP control. While the covers have been effective for TPP management, the green peach aphid (GPA, Myzus persicae) has been found in large numbers under the mesh crop covers. This study investigated the ability of the GPA to penetrate different mesh hole sizes. Experiments using four sizes (0.15 × 0.15, 0.15 × 0.35, 0.3 × 0.3 and 0.6 × 0.6 mm) were carried out under laboratory conditions to investigate: (i) which mesh hole size provided the most effective barrier to GPA; (ii) which morph of adult aphids (apterous or alate) and/or their progeny could breach the mesh crop cover; (iii) would leaves touching the underside of the cover, as opposed to having a gap between leaf and the mesh, increase the number of aphids breaching the mesh; and (iv) could adults feed on leaves touching the cover by putting only their heads and/or stylets through it? No adult aphids, either alate or apterous, penetrated the mesh crop cover; only nymphs did this, the majority being the progeny of alate adults. Nymphs of the smaller alatae aphids penetrated the three coarsest mesh sizes; nymphs of the larger apterae penetrated the two coarsest sizes, but no nymphs penetrated the smallest mesh size. There was no statistical difference in the number of aphids breaching the mesh crop cover when the leaflets touched its underside compared to when there was a gap between leaf and mesh crop cover. Adults did not feed through the mesh crop cover, though they may have been able to sense the potato leaflet using visual and/or olfactory cues and produce nymphs as a result. As these covers are highly effective for managing TPP on field potatoes, modifications of this protocol are required to make it effective against aphids as well as TPP.

Mortality of Potato Psyllid (Hemiptera: Triozidae) on Host Clippings Inoculated With Ergot Alkaloids.

Our previous study provided correlative evidence that morning glory species harboring endophytic fungi (Periglandula) are resistant to potato psyllid [Bactericera cockerelli (Šulc)], whereas species free of fungi often allowed psyllid development. In this study, we manipulated levels of ergot alkaloids in host tissues by inoculating clippings from potato plants with extracts from morning glories that harbor Periglandula [Ipomoea leptophylla Torrey, Ipomoea imperati (Vahl) Grisebach, Ipomoea tricolor Cavanilles, Ipomoea pandurata (L.) G. F. Meyer, and Turbina corymbosa (L.)] and one species (Ipomoea alba L.) that does not harbor the endophyte. Ergot alkaloids (clavines, lysergic acid amides, and ergopeptines) were detected in potato clippings, thus confirming that leaves had taken up compounds from solutions of crude extracts. Psyllid mortality rates on inoculated clippings ranged between 53 and 93% in treatments producing biochemically detectable levels of alkaloids, when compared with 15% mortality in water controls or the alkaloid-free I. alba. We then tested synthetic analogs from each of the three alkaloid classes that had been detected in the crude extracts. Each compound was assayed by inoculating clippings of two host species (potato and tomato) at increasing concentrations (0, 1, 10, and 100 µg/ml in solution). Psyllids exhibited a large and significant increase in mortality rate beginning at the lowest two concentrations, indicating that even very small quantities of these chemicals led to mortality. Feeding by nymphs on artificial diets containing synthetic compounds resulted in 100% mortality within 48 h, irrespective of compound. Further testing of ergot alkaloids to characterize the mode of action that leads to psyllid mortality is warranted.

Seasonal Population Dynamics of Potato Psyllid (Hemiptera: Triozidae) in the Columbia River Basin.

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.

Drought stress and pathogen infection alter feeding behavior of a phytopathogen vector

AbstractThe impact of drought stress on tripartite plant‐pathogen‐vector interactions constitutes a complex and largely understudied field of plant‐insect interaction. A number of studies explored these topics using aphid vectors of plant pathogens, but few have considered the interactions between drought‐stressed plants and pathogen‐transmitting psyllids. The potato psyllid, Bactericera cockerelli (Šulc) (Hemiptera: Triozidae), is one of the key pests of solanaceous crops in the USA that causes direct injury as well as indirect injury through transmission of a bacterial pathogen, Candidatus Liberibacter solanacearum (Lso), the causal agent of zebra chip. Previous studies explored the impact of Lso infection and drought stress on B. cockerelli development and reproductive rate separately, but no research to date has evaluated whether drought stress and Lso infection alter feeding behavior of the insects. We explored this using the electrical penetration graph (EPG) technique and monitored feeding behavior of Lso‐infected and uninfected potato psyllids on well‐watered and drought‐stressed tomato (Solanum lycopersicum L., Solanaceae). We found that drought stress had a significant effect on feeding behavior associated with salivation into the phloem and phloem ingestion, both linked to Lso transmission. Furthermore, infected potato psyllids in particular produced a higher number of events associated with these feeding behaviors and remained in these phases longer in well‐watered plants than in plants that were under drought stress. We also reported a new and previously undescribed waveform H of unknown biological function that was produced by the psyllids. This is the first study that considered the impact of bacterial infection and concomitant drought stress on feeding behavior of an insect quantified using EPG.

Tamarixia triozae, an important parasitoid of Bactericera cockerelli: circadian rhythms and their implications in pest management

Tamarixia triozae (Burks) (Hymenoptera: Eulophidae) is an important primary parasitoid of Bactericera cockerelli (Sulc) (Hemiptera: Triozidae). This study aimed to unveil the parasitoid’s circadian rhythms and provide information for enhancement of its biological control. Most emergence occurred in the morning and most mating took place early next morning. Oviposition only occurred during the daytime, peaking between mid-morning and mid-afternoon while host feeding had three peaks in the early morning, late afternoon and dawn, respectively. We demonstrate that circadian activity peaks for different life functions did not overlap, suggesting that T. triozae have developed strategies for maximal fitness gain. These findings have implications in pest management, which can be tested under field conditions. For example, release of sexually mature and host-fed adults in the early morning may help achieve better control. Moreover, insecticide sprays, when necessary, may be applied as late in the evening as possible to reduce side effects on this parasitoid.

Electron beam irradiation induces DNA endoreplication in holometabolous juvenile insects: a rapid flow cytometry-based diagnosis

Ionizing radiation including electron beam (eBeam) technology has been used as a quarantine measure around the world for transboundary shipment of agricultural products. Since the treatment goal of this technology is not to instantly kill insects but to cause them to be sterile, an apparent challenge is how to ensure that the agricultural commodities have been exposed to ionizing radiation if live insects are found. Because irradiation affects DNA synthesis and cell division, we investigated the feasibility of using flow cytometry detection of eBeam irradiation-induced ploidy change as a diagnostic tool. All eBeam-treated holometabolous insects tested including cowpea bruchid (Callosobruchus maculatus), corn earworm (Helicoverpa zea) and fruit fly (Drosophila melanogaster) displayed significantly higher proportions of polyploid cells than their respective unirradiated controls. However, such increased DNA ploidy was mostly absent in irradiated hemimetabolous sand field cricket (Gryllus firmus), green peach aphid (Myzus persicae) and potato/tomato psyllid (Bactericera cockerelli). Further studies with representative holometabolous insects revealed that the eBeam-triggered DNA endoreplicative response was strong in larvae, but became weaker as insects continued to develop into pupae and was even diminished in adults. Therefore, the flow cytometry-based method has the potential to be developed into a diagnostic tool to determine whether juvenile insects found on agricultural shipments, particularly those that undergo complete metamorphosis, have received irradiation as a quarantine treatment. This simple and rapid detection method could potentially resolve the dilemma that occurs in border control and domestic movement of plant material and products from areas under quarantine.

Can Vibrational Playbacks Disrupt Mating or Influence Other Relevant Behaviours in Bactericera cockerelli (Triozidae: Hemiptera)?

Behaviours of insects can be manipulated by transmitting vibrational signals to host plants in order to develop pest management techniques. Bactericera cockerelli is an important pest and uses vibrations for mate-finding. In order to design a future control strategy for B. cockerelli, three different bioassays were performed to assess whether vibrational signals could affect relevant behaviours. Single males or pairs were treated with a female playback in test 1 and 2, respectively. In test 3, mixed sex groups received either different disturbance playbacks. The use of a female playback significantly reduced the mating success of males, since they were attracted towards the source of the stimulus. Moreover, test 2 revealed that B. cockerelli females are competitive, since they used their signals to cover the playback and to duet with males, while in test 3, the disturbance playback, consisting of broadband noises significantly reduced male signalling activity. However, none of the treatments of test 3 negatively affected the mating success of males, which tended to mount the other conspecifics present on the same leaf. The role of vibrations in sexual communication and their potential application as control technique for B. cockerelli are discussed as well.

Potential Distribution and the Risks of Bactericera cockerelli and Its Associated Plant Pathogen Candidatus Liberibacter Solanacearum for Global Potato Production

The tomato potato psyllid (TPP), Bactericera cockerelli, is a psyllid native to North America that has recently invaded New Zealand and Australia. The potential for economic losses accompanying invasions of TPP and its associated bacterial plant pathogen Candidatus Liberibacter solanacearum (CLso), has caused much concern. Here, we employed ecological niche models to predict environments suitable for TPP/CLso on a global scale and then evaluated the extent to which global potato cultivation is at risk. In addition, at a finer scale the risk to the Australian potato acreage was evaluated. A total of 86 MaxEnt models were built using various combinations of settings and climatic predictors, and the best model based on model evaluation metrics was selected. Climatically suitable habitats were identified in Eurasia, Africa, South America, and Australasia. Intersecting the predicted suitability map with land use data showed that 79.06% of the global potato cultivation acreage, 96.14% of the potato production acreage in South America and Eurasia, and all the Australian potato cropping areas are at risk. The information generated by this study increases knowledge of the ecology of TPP/CLso and can be used by government agencies to make decisions about preventing the spread of TPP and CLso across the globe.

Effect of the level of "Candidatus Liberibacter solanacearum" infection on the development of zebra chip disease in different potato genotypes at harvest and post storage.

Potato psyllid (Bactericera cockerelli Sulc)-transmitted “Candidatus Liberibacter solanacearum” (Lso) has been negatively impacting the potato industry in the United States as well as other potato-producing countries. Lso has been linked to a condition known as zebra chip (ZC) that affects yield and quality of potato tubers. Efforts to find sources of resistance to ZC have primarily focused on greenhouse evaluations based on a single inoculation time prior to harvest. Plant response to infection, however, could be influenced by the developmental stage of the host plant, and ZC may continue to develop after harvest. The objectives of this study were to quantify Lso inoculation success, Lso titer, ZC severity and Lso development during storage in eight potato genotypes. These evaluations were conducted on plants infested with Lso-positive psyllids at 77, 12, and 4 days before vine removal (DBVR). The evaluated genotypes were categorized according to their relative resistance to Lso and tolerance to ZC symptoms. Lso inoculation success in the genotype family A07781, derived from Solanum chacoense, was lower than that of the susceptible control (‘Russet Burbank’). A07781-4LB and A07781-3LB genotypes were characterized relatively resistant to the pathogen and highly tolerant to ZC symptoms, while A07781-10LB was categorized as susceptible to Lso but relatively tolerant to symptom expression. In stored potatoes, increase in Lso concentrations was observed for all infestation times. However, significantly higher Lso titer was detected in tubers infested 12 DBVR and the effect was similar across genotypes. Overall, the A07781 family can be considered as a promising source of resistance or tolerance to ZC.

Concanavalin A Toxicity Towards Potato Psyllid and Apoptosis Induction in Midgut Cells.

Concanavalin A (ConA), a legume lectin, has been drawing increasing attention in recent years concerning its toxicity against insects and its potential application in pest management. In an attempt to evaluate the effect of ConA on potato psyllid (Bactericera cockerelli), an economically important pest of solanaceous crops, the effect of ConA on potato psyllid survival, psyllid gut nuclear morphology, and expression of psyllid caspase genes were evaluated. Our results determined that artificial diet-feeding assays using ConA had deleterious effects on potato psyllids, resulting in significant psyllid mortality following ingestion. We also found that an apoptotic response was induced by ConA in psyllid midgut cells, which was demonstrated by the DNA fragmentation and abnormal nuclear architecture in the midgut cells. Following ConA ingestion, there was also upregulation of caspase genes in the psyllid midguts. Therefore, a key mechanism behind ConA toxicity towards potato psyllid probably involves the induction of apoptosis in midgut cells. This study could provide a better understanding of the mechanisms underlying ConA toxicity in insects and be a stepping stone towards the development of new psyllid control strategies based on plant lectins.

Effects of Potato Psyllid Vector Density and Time of Infection on Zebra Chip Disease Development after Harvest and during Storage

“Candidatus Liberibacter solanacearum” (Lso) (=“Candidatus Liberibacter psyllarous”) is an uncultured, phloem-limited bacterium that is associated with zebra chip disease (ZC) in potato (Solanum tuberosum L.) and transmitted by the potato psyllid (Bactericera cockerelli (Šulc)). Vector density and timing of infection have been shown to affect ZC prevalence at harvest; however, little work has been done on disease development during storage. Here we confirm with field-cage trials that ZC prevalence at harvest was greater with increased time between inoculation and vine kill. Moreover, we show that with Pacific Northwest growing conditions, ZC can develop over time during storage. Plants inoculated 2 to 3 weeks before vine kill showed little or no ZC symptoms in tubers at harvest, but higher prevalence of symptoms after 3 months in storage. For plants inoculated at 4 to 5 weeks before vine kill, tubers exhibited notable symptoms at harvest, but still showed evidence of symptom development after storage. Plants inoculated within 1 week before vine kill exhibited little or no risk of ZC in tubers at harvest or after storage. Higher vector density tended to contribute to ZC prevalence, but was far less important than timing of infection. These results underscore the potential danger of underestimating ZC prevalence at harvest for tubers being stored long term, and suggest that plants at risk of Lso infection should be protected from potato psyllids until at least 2 weeks before vine kill.

Prototype 3D-Printed Traps Capture Bactericera cockerelli (Šulc) (Hemiptera: Triozidae) Directly into Preservative for Improved Detection of “Candidatus Liberibacter solanacearum”

Potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae), is a key pest of potato (Solanum tuberosum L.) and other solanaceous crops (Solanales: Solanaceae) as a vector of “Candidatus Liberibacter solanacearum” (Lso), the pathogen associated with zebra chip disease of potato. Potato psyllid populations typically are monitored using sticky card traps, and psyllids collected from sticky traps often are subjected to polymerase chain reaction (PCR) to monitor the incidence of Lso within psyllid populations. Psyllids collected from sticky traps are often mangled, desiccated, and coated with sticky residue, which may interfere with detection of Lso by PCR. A recently developed prototype 3-dimensional-printed trap that captures insects directly into a preservative (70% ethanol) was previously tested for monitoring psyllid populations. The capture of psyllids directly into a preservative may reduce degradation of DNA or protect specimens from PCR-inhibiting contaminants, thus improving the detection of Lso by PCR. Our goal was to compare the detectability of Lso in psyllids captured into preservative (prototype trap) to that in psyllids removed from sticky card traps. Overall, detection rates were higher in psyllids from the prototype trap than from sticky card traps. This improvement in Lso detection appeared to be partly due to the specimens yielding more DNA of higher quality. Results of this study demonstrate that compared with sticky card traps, a trap that captures psyllids directly into a preservative provides higher quality specimens for collection of molecular data, including pathogen diagnosis, population genetics, and molecular gut content analysis.

A diagnostic real-time PCR assay for the rapid identification of the tomato-potato psyllid, Bactericera cockerelli (Šulc, 1909) and development of a psyllid barcoding database.

The accurate and rapid identification of insect pests is an important step in the prevention and control of outbreaks in areas that are otherwise pest free. The potato-tomato psyllid Bactericera cockerelli (Šulc, 1909) is the main vector of 'Candidatus Liberibacter solanacearum' on potato and tomato crops in North America and New Zealand; and is considered a threat for introduction in Europe and other pest-free regions. This study describes the design and validation of the first species-specific TaqMan probe-based real-time PCR assay, targeting the ITS2 gene region of B. cockerelli. The assay detected B. cockerelli genomic DNA from adults, immatures, and eggs, with 100% accuracy. This assay also detected DNA from cloned plasmids containing the ITS2 region of B. cockerelli with 100% accuracy. The assay showed 0% false positives when tested on genomic and cloned DNA from 73 other psyllid species collected from across Europe, New Zealand, Mexico and the USA. This included 8 other species in the Bactericera genus and the main vectors of 'Candidatus Liberibacter solanacearum' worldwide. The limit of detection for this assay at optimum conditions was 0.000001ng DNA (~200 copies) of ITS2 DNA which equates to around a 1:10000 dilution of DNA from one single adult specimen. This assay is the first real-time PCR based method for accurate, robust, sensitive and specific identification of B. cockerelli from all life stages. It can be used as a surveillance and monitoring tool to further study this important crop pest and to aid the prevention of outbreaks, or to prevent their spread after establishment in new areas.

Parasitism, host feeding, and transgenerational effects of three insecticides on the eulophid parasitoid Tamarixia triozae when exposed in the immature stages.

The ectoparasitoid Tamarixia triozae is a promising biological control agent of the tomato psyllid, Bactericera cockerelli, based on its high parasitism rates on different crops. The parasitism, host feeding, and transgenerational effects (in terms of sex ratio) of T. triozae females exposed to three insecticides (soybean oil, imidacloprid, and abamectin) as eggs, larvae, and pupae were evaluated when a mixture of second, third, fourth, and fifth instars of the host B. cockerelli was offered. The concentrations bioassayed of each insecticide corresponded to the minimum field-registered concentration [MiFRC] and one-half the MiFRC. No parasitism of B. cockerelli second instars was recorded when parasitoid's females were exposed in any of the three immature stages to any of the insecticides. In contrast, in some cases, parasitism of T. triozae females treated as eggs, larvae, or pupae with soybean oil and imidacloprid was reduced in third, fourth, or fifth instar. In most cases, the host feeding was reduced in second and third instar of the host B. cockerelli when T. triozae females were treated as eggs, larvae, or pupae. Any insecticide modified the sex ratio in the F2 generation. In conclusion, both parasitism and host feeding were affected by the insecticides depending on the concentration and on the nymphal instar of the host B. cockerelli offered.

Effects of temperature and tomato variety on development stages of Bactericera cockerelli (Sulc) (Hemiptera: Triozidae)

Tomato is one of the most consumed vegetables per capita in the world; it is grown both in the open and in greenhouses. Under these conditions, the pest is considered a severe problem, especially considering Bactericera cockerelli Sulc. Therefore, in this experiment, the life history of this pest insect in two tomato varieties: “Charanda F1” and “Rafaello” the differences in the development stages of the insect, the mean temperatures of two cycles, and the accumulated heat units determined. The work consisted of evaluating the development of the instars of B. cockerelli during two crop cycles in both varieties, as well as the accumulation of heat units to differentiate the distinct instars. The insect populations developed in the Rafaello variety had shorter lives and showed a higher death rate of eggs than did those that developed in Charanda F1. The temperature was another determining factor; when the temperature remained low, the insect biological cycle was longer. Likewise, heat units were different between the two varieties; in Rafaello, 598.13 heat units needed while in Charanda F1, only 464.98. The differences may be due to the morphological characteristics of each variety, as the presence of trichomes and oils. Thus, we suggest that these variables studied in future research works.

Landscape structure and climate drive population dynamics of an insect vector within intensely managed agroecosystems.

Characterizing factors affecting insect pest populations across variable landscapes is a major challenge for agriculture. In natural ecosystems, insect populations are strongly mediated by landscape and climatic factors. However, it has proven difficult to evaluate if similar factors predict pest dynamics in agroecosystems because control tactics exert strong confounding effects. We addressed this by assessing whether species distribution models could effectively characterize dynamics of an insect pest in intensely managed agroecosystems. Our study used a regional multi-year data set to assess landscape and climatic drivers of potato psyllid (Bactericera cockerelli) populations, which are often subjected to calendar-based insecticide treatments because they transmit pathogens to crops. Despite this, we show that psyllid populations were strongly affected by landscape and climatic factors. Psyllids were more abundant in landscapes with high connectivity, low crop diversity, and large natural areas. Psyllid population dynamics were also mediated by climatic factors, particularly precipitation and humidity. Our results show that many of the same factors that drive insect population dynamics in natural ecosystems can have similar effects in an intensive agroecosystem. More broadly, our study shows that models incorporating landscape and climatic factors can describe pest populations in agroecosystems and may thus promote more sustainable pest management.

Potato Psyllid (Hemiptera: Triozidae) Behavior on Three Potato Genotypes With Tolerance to 'Candidatus Liberibacter solanacearum'.

The potato/tomato psyllid Bactericera cockerelli (Šulc) transmits ‘Candidatus Liberibacter solanacearum’ (Lso) (also known as ‘Candidatus Liberibacter psyllaurous’), the bacterium associated with zebra chip disease (ZC) in potato. When disease incidence is high, ZC causes large economic losses through reductions in potato yield and tuber quality. No commercial potato variety has been found totally resistant to the pathogen. We evaluated host acceptance behaviors using no-choice assays on three breeding clones derived from Solanum chacoense Bitter with putative tolerance to Lso and/or ZC as part of an effort to determine whether the disease tolerance observed in those breeding clones was related to effects on psyllid settling behavior. We also counted the number of eggs laid and nymphs hatched on the different genotypes to observe any differences in reproduction. The potato variety ‘Russet Burbank’ was used as a susceptible control. Probing frequency and female walking duration were greater on Russet Burbank than the other genotypes. Oviposition did not differ among genotypes. However, female psyllids on two of the Lso-tolerant genotypes displayed reduced fertility 18–24 d after confinement with a male, relative to females on Russet Burbank. These results suggest that although the germplasms display minor abiotic activity on psyllid fertility, tolerance to Lso may be more strongly linked with plant tolerance to the pathogen rather than effects on host acceptance behaviors.

Non-invasive diagnostics of Liberibacter disease on tomatoes using a hand-held Raman spectrometer.

Hand-held Raman spectroscopy can be used for confirmatory, non-invasive and non-destructive detection and identification of two haplotypes of Liberibacter disease on tomatoes. Using this spectroscopic approach, structural changes in carotenoids, xylan, cellulose and pectin that are associ-ated with this bacterial disease can be determined. 'Candidatus Liberibacter solanacearum' (Lso) is a phloem-limited Gram-negative bacterium that infects crops worldwide. In North America, two haplotypes of Lso (LsoA and LsoB) are transmitted by the potato psyllid, Bactericera cockerelli (Sulč), and infect many solanaceous crops such as potato and tomato. Infected plants exhibit chlorosis, severe stunting, leaf cupping, and scorching. Polymerase chain reaction (PCR) and potato tuber frying are commonly used methods for diagnostics of the plant disease caused by Lso. However, they are time-consuming, costly, destructive to the sample, and often not sensitive enough to detect the pathogen in the early infection stage. Raman spectroscopy (RS) is a noninvasive, nondestructive, analytical technique, which probes chemical composition of analyzed samples. In this study, we demonstrate that Lso infection can be diagnosed by non-invasive spectroscopic analysis of tomato leaves three weeks following infection, before the development of aerial symptoms. In combination with chemometric analyses, Raman spectroscopy allows for 80% accurate diagnostics of Liberibacter disease caused by each of the two different haplotypes. This diagnostics approach is portable and sample agnostic, suggesting that it could be utilized for other crops and could be conducted autonomously.