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Assessing the risk of containerized citrus contributing to Asian citrus psyllid ( Diaphorina citri ) spread in California: Residence times and insecticide residues at retail nursery outlets
Abstract
For phytophagous insects and plant pathogens, the unregulated movement of plant material can inadvertently promote long-distance spread, facilitating biological invasions. Such human-assisted spread has contributed to the invasion of the Asian citrus psyllid (Diaphorina citri), a vector of the pathogens associated with huan-glongbing. Following the detection of D. citri in California, regulations were instituted to limit movement of D. citri host plants, by mandating insecticide treatments of citrus nursery stock, and limiting the amount of time host plants can reside at retail sites. We used a set of surveys and a field experiment to evaluate how well these steps mitigate the threat of containerized citrus playing a role in D. citri spread. A qualitative analysis of data collected by state regulators throughout Southern California found that containerized citrus may reside at retail sites for extended durations, in extreme cases upwards of 2 years post treatment. More detailed surveys at nearly 30 retail sites in Southern California showed that the majority of citrus plants were present past the 90 day regulatory limit, 33% had been treated more than 1 year prior, and 90% had imidacloprid residues below those known to be effective against D. citri nymphs. A field experiment confirmed that imidacloprid residues in trees grown in containers were affected by citrus species, watering level, soil mix, and time since treatment. Overall, plants had D. citri-effective residues for approximately 12 weeks, suggesting that imidacloprid treatments should protect the majority of containerized citrus against D. citri for approximately the duration of the 90 day regulatory limit. To further protect trees from infestation, nurseries should be encouraged to adopt practices that maximize the effectiveness of insecticide treatments, including ways to reduce residence times of host plants at retail sites.
... Transmission of both the CLas and CLam bacteria occurs due to feeding of the ACP (Grafton-Cardwell, Stelinski, & Stansly, 2013;Hall, Richardson, Ammar, & Halbert, 2013). ACP and HLB have spread throughout the world mostly via worldwide trade (Byrne et al., 2018) and now exist in nearly all citrus producing regions (Hall et al., 2013). The cost of this disease to the citrus industry is huge, and interventions to prevent its spread and reduce the deleterious effects of the disease are, for the most part, ineffective (Hodges & Spreen, 2012). ...
... Although California has had incursions of the disease, with the first occurring in 2012 (Kumagai et al., 2013), all have been in trees at residential properties and hence the citrus industry in California is currently free from disease (Byrne et al., 2018). Similarly, the Iberian peninsula has had no cases of HLB (Cocuzza et al., 2017). ...
... There is no effective cure for HLB except to remove the diseased trees once infected. In recent years, the incidence of HLB has caused over $3.6 billion of loss in Florida (Byrne et al. 2018), and about 45 million citrus trees have been removed in Ganzhou, China (Zhou 2018). The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), is one of the most damaging pests in citrus industry worldwide because it acquires the HLB pathogens from infected plants and subsequently transmits into healthy plants during the feeding processes (Ammar et al. 2013;Song et al. 2020). ...
Diaphorina citri Kuwayama is a serious insect pest of citrus worldwide due to the capacity to transmit causal agent of the huanglongbing. Mineral oils are recommended in the integrated pest management programs to prevent resistance development. The primary objective of this study was to determine emergence inhibition and antifeedant effect of three mineral oils with similar n-paraffin carbon number against D. citri. The results of topical contact toxicity showed that Antong was the most toxic with 50% lethal concentration value of 189 ng/insect. Each mineral oil at the concentrations of 0.1, 0.2 and 0.5% (v/v) significantly inhibited the emergence of adults from treated fifth-instar nymphs, and 0.5% (v/v) of the oils had a long residue activity that they inhibited over 56% adult emergence up to 10 days. We found significant repellency of D. citri from citrus tree resets that were treated with mineral oils compared with control. 0.5% (v/v) of the mineral oils significantly inhibited feeding of D. citri adults with reduction of 39–68% honeydew, and the nymphs that fed on citrus leaves treated with different concentrations raised heads and upper abdomens to form a half-erect posture. Our studies indicated that mineral oils could effectively reduce or suppress the spread of HLB by repellency and less feeding, as well as emergence inhibition to reduce D. citri populations.
Huanglongbing (HLB), formerly known as greening, is a bacterial disease restricted to some Asian and African regions until two decades ago. Nowadays, causing bacteria and their vectors have spread to almost all citrus producing regions, and it is currently considered the most devastating citrus disease. HLB management can be approached in terms of prevention, limiting or avoiding pathogen and associated vectors to reach an area, or in terms of control, trying to reduce the impact of the disease by adopting different cultural strategies depending on infestation/infection levels. In both cases, control of psyllid populations is currently the best way to stop HLB spread. Best cultural actions (CHMAs, TPS system) to attain this goal and thus, able to limit HLB spread, and ongoing research in this regard is summarized in this review.
There are specific regulations in the USA for the inter-state shipment of containerized citrus from production nurseries located within Diaphorina citri Kuwayama (Asian citrus psyllid; ACP) quarantine zones. To ensure trees are protected from the insect, nurseries must treat trees with an approved systemic neonicotinoid at least 30 days, and not more than 90 days, before trees can be shipped. The objective of this study was to reevaluate the necessity for a 30-day pre-shipment restriction by providing regulators with further data on the uptake of imidacloprid, thiamethoxam and dinotefuran, during the days immediately following treatments. In previous studies, ACP-effective thresholds were determined for 1-year old containerized citrus trees by correlating residue concentrations in leaf tissue with ACP efficacy. In this study, we used target concentrations to compare the uptake and retention of these neonicotinoids in 4 cultivars of 1-year old containerized citrus trees. ACP-effective thresholds were achieved within 3 days of treatment with the current lowest label rate (6.43 g AI/m³ soil) of generic formulations of imidacloprid, and within 1 day of treatment with the maximum label rate (97 g AI/m³ soil) of the name brand formulation Admire Pro®. The establishment of dinotefuran at ACP-effective thresholds was erratic in citrus cultivars, and residues of both dinotefuran and thiamethoxam had largely dissipated before the 30-day pre-shipment period had expired. The uptake and retention of all three neonicotinoids were significantly compromised under excessive watering (400% ET), although ACP-effective thresholds were still achieved with all imidacloprid treatment rates and thiamethoxam within 3 days. Overall, our results strongly support shortening the 30-day pre-shipment restriction to at most 3 days for trees treated with either imidacloprid or thiamethoxam. And, dinotefuran should be removed from the list of systemic insecticides approved for quarantine treatments.
Predicting where crop pests and diseases can occur, both now and in the future under different climate change scenarios, is a major challenge for crop management. One solution is to estimate the fundamental thermal niche of the pest/disease to indicate where establishment is possible. Here we develop methods for estimating and displaying the fundamental thermal niche of pests and pathogens and apply these methods to Huanglongbing (HLB), a vector-borne disease that is currently threatening the citrus industry worldwide.
We derive a suitability metric based on a mathematical model of HLB transmission between tree hosts and its vector Diaphorina citri , and incorporate the effect of temperature on vector traits using data from laboratory experiments performed at different temperatures. We validate the model using data on the historical range of HLB.
Our model predicts that transmission of HLB is possible between 16°C and 33°C with peak transmission at ~25°C. The greatest uncertainty in our suitability metric is associated with the mortality of the vectors at peak transmission, and fecundity at the edges of the thermal range, indicating that these parameters need further experimental work.
We produce global thermal niche maps by plotting how many months each location is suitable for establishment of the pest/disease. This analysis reveals that the highest suitability for HLB occurs near the equator in large citrus-producing regions, such as Brazil and South-East Asia. Within the northern hemisphere, the Iberian peninsula and California are HLB suitable for up to 7 months of the year and are free of HLB currently.
Policy implications . The thermal niche map indicates the places at greatest risk of HLB establishment should the disease enter these regions. This indicates where surveillance should be focused to prevent establishment. Our mechanistic method can be used to predict new areas for HLB transmission under different climate change scenarios and is easily adapted to other vector-borne diseases.
Biological invasions are governed by spatial processes that tend to be distributed in non-random ways across landscapes. Characterizing the spatial and temporal heterogeneities of the introduction, establishment, and spread of non-native insect species is a key aspect of effectively managing their geographic expansion. The Asian citrus psyllid (Diaphorina citri), a vector of the bacterium associated with huanglongbing (HLB), poses a serious threat to commercial and residential citrus trees. In 2008, D. citri first began expanding northward from Mexico into parts of Southern California. Using georeferenced D. citri occurrence data from 2008–2014, we sought to better understand the extent of the geographic expansion of this invasive vector species. Our objectives were to: 1) describe the spatial and temporal distribution of D. citri in Southern California, 2) identify the locations of statistically significant D. citri hotspots, and 3) quantify the dynamics of anisotropic spread. We found clear evidence that the spatial and temporal distribution of D. citri in Southern California is non-random. Further, we identified the existence of statistically significant hotspots of D. citri occurrence and described the anisotropic dispersion across the Southern California landscape. For example, the dominant hotspot surrounding Los Angeles showed rapid and strongly asymmetric spread to the south and east. Our study demonstrates the feasibility of quantitative invasive insect risk assessment with the application of a spatial epidemiology framework.
The Asian citrus psyllid, Diaphorina citri Kuwayama, was discovered in Florida in 1998. It can be one of the most serious pests of citrus if the pathogens that cause citrus greening disease (huanglongbing) are present. Citrus greening recently has been reported in Brazil by Fundecitrus, Brazil. The establishment of D. citri in Florida increases the possibility that the disease may become established. Diaphorina citri can be separated from about 13 other species of psyllids reported on citrus. The biology of D. citri makes it ideally suited to the Florida climate. Only two species, D. citri and Trioza erytreae (del Guercio), have been implicated in spread of citrus greening, a disease caused by highly fastidious phloem-inhabiting bacteria. The disease is characterized by blotchy mottle on the leaves, and misshapen, poorly colored off-tasting fruit. In areas where the disease is endemic, citrus trees may live for only 5-8 years and never bear usable fruit. The disease occurs throughout much of Asia and Africa south of the Sahara Desert, on several small islands in the Indian Ocean, and in the Saudi Arabian Peninsula. Transmission of citrus greening occurs primarily via infective citrus psyllids and grafting. It is transmissible experimentally through dodder and might be transmitted by seed from infected plants and transovarially in psyllid vectors. Citrus greening disease is restricted to Citrus and close citrus relatives because of the narrow host range of the psyllid vectors. Management of citrus greening disease is difficult and requires an integrated approach including use of clean stock, elimination of inoculum via voluntary and regulatory means, use of pesticides to control psyllid vectors in the citrus crop, and biological control of psyllid vectors in non-crop reservoirs. There is no place in the world where citrus greening disease occurs that it is under completely successful management. Eradication of citrus greening disease may be possible if it is detected early. Research is needed on rapid and robust diagnosis, disease epidemiology, and psyllid vector control.
Huanglongbing (HLB) was first identified near Araraquara in the central region of São Paulo State (SPS), Brazil, in March 2004. As of November 2009, HLB was present in 242 of the 425 citrus-growing municipalities of SPS. In April 2009, the current total number of symptomatic trees was estimated to be ca. 2.0 million (ca. 0.87%) and 4 million trees had already been removed. The recommended measures for HLB management are based on two phytopathologically sound principles: (i) inoculum reduction by frequent removal of HLB-affected trees and (ii) control of psyllid vector populations by insecticide treatments. The goal of this management strategy is to prevent as many trees as possible from becoming infected with the HLB pathogen. After five or six years of HLB management, several SPS citrus farms have shared their results on HLB control. Here we present data from eighteen farms where the recommended measures have been applied since 2004 or 2005 in SPS, showing that HLB can be controlled. SPS is one of the first regions in the world where preventive control against Asian HLB has been carried out on a large scale under various conditions and found to be successful when the recommended measures were applied rigorously. However, only one-third of SPS citrus trees are under effective HLB-management and they are located on large farms, where HLB management is easier than on small farms. The majority of trees in small and medium-sized groves commonly do not benefit from HLB management. This is the reason that HLB incidence in SPS has increased in spite of HLB management. Many groves in which no HLB management is carried out have high proportions of HLB-affected trees and large populations of HLB-positive psyllid vectors. These groves are the major obstacle to HLB management in SPS. These severely affected groves endanger the very existence of the Brazilian citrus industry. When such groves are within a ca. 4km range from well-man-aged farms, their psyllids invariably invade and contaminate the latter farms. SPS has legal tools, which make possible the removal of contaminating groves, but the laws are not strictly enforced. Costs of HLB management vary considerably, but inspections range from $4 to 17 $US each per ha, and insecticide treatments from about $US 240 to > $1,000 per ha annually, depending on the products used, the means and frequency of application. HLB management as described here is only a short-term solution to keep the citrus industry alive and to buy time for long-term solutions, probably based on engineered citrus genotypes, to become available, hopefully, in five to ten years.
In the past 5 years, two homopteran pests of citrus have become established in Florida. Both are pests primarily because of their ability to transmit serious citrus pathogens. Brown citrus aphid [Toxoptera citricida (Kirkaldy)], the vector of citrus tristeza virus (CTV), was found in Florida in late 1995. The original infested area included parts ofDade and Broward Counties in south Florida. Jn2 years, it had colonized most ofpeninsular Florida. First finds in most counties were on outdoor citrus trees. The rate of colonization for brown citrus aphid in Florida was similar to the rate published for other invasive aphid species. Asian citrus psyllid [Diaphorina citri Kuwayama], the vector of citrus greening pathogens, was first found in Florida in June 1998. The original infested area included coastal Palm Beach County, and parts of northern Broward and southern Martin Counties. In 2 years, it colonized the southern half' of the Florida peninsula. In south Florida, Asian citrus psyllids could be found in the landscape, but in central Florida, only plants for sale in retail stores were found infested. Thus, it appears that the natural rate of colonization for Asian citrus psyllid is slower than that for brown citrus aphid; however, Asian citrus psyllid was more likely than brown citrus aphid to be moved on plants for sale in Florida. Surveys have been made for the pathogens transmitted by these pests. There is no evidence of citrus greening disease in Florida; however, we have seen an increase in both incidence and severity of CTV in areas where brown citrus aphid has been present 2 years fIr longer. Toxoptera citricida (Kirkaldy) is the most efficient vector of citrus tristeza virus (CTV). Introduction of Ihis aphid into various regions of Ihe Western Hemisphere has preceded serious outbreaks of CTV. Similarly, Diaphorina citri Kuwayama is a serious pest of citrus primarily because it is a vector of the pathogens that cause citrus greening disease or huanglongbing. Citrus greening has nOI been found in the Western Hemisphere, but D. cirri has been present in Soulh America for several decades. Florida is at risk for introductions of exotic pests and diseases due to the large amount of incoming commer-cial and tourist tramc. Additionally, Florida residents sometimes may smuggle plant materials from overseas. The Florida Department of Agriculture and Consumer Services, Division ofPlalll Industry (DPl), employs over 100 inspectors whose job it is to find new pests. This paper reports the establishment of two new citrus pests, D. citri and T. citricida. Prior to the arrival of T. citricida, there was a statewide baseline survey done to determine the incidence and make-up of CTV strains in Florida (Brown and Davison, 1997). No surveys had been done for citrus greening prior to the introduction of D. citri.
In September 2001, the presence of the Asian citrus psylla, Diaphorina citri Kuwayama (Homoptera:Psyllidae) in Texas was confirmed. It was found on nursery citrus seedlings and on an orange jessamine (Murraya spp.) hedge. Since then, the insect has been observed in other parts of the Lower Rio Grande Valley. This insect is an efficient vector of the serious bacterial disease of citrus, huanglongbing (greening disease).
Huanglongbing (HLB), also known as citrus greening, is one of the most destructive citrus diseases worldwide and is seen as a major threat to the multimillion dollar citrus industry in California. The vector of the two bacterial species associated with this disease, Candidatus Liberibacter asiaticus and Ca. L. americanus, is the Asian citrus psyllid (ACP), Diaphorina citri (4). ACP was detected in California in August of 2008 and has since been detected in nine counties in southern California. As part of a long term survey and testing program for the ACP carrying the HLB associated bacteria, groups of ACP nymphs and adults were submitted to the Jerry Dimitman Citrus Research Board/Citrus Pest and Disease Prevention Program Laboratory in Riverside, CA. In March 2012, DNA extracted using the Qiagen MagAttract 96 DNA plant kit (QIAGEN Inc., 27220 Turnberry Lane, Suite 200, Valencia, CA 91355) from a group of three ACP adults tested positive for Ca. L. asiaticus with the real-time PCR assay developed by Li et...
The Asian citrus psyllid, Diaphorina citri Kuwayama, was reported for the first time in Florida in June 1998, and huanglongbing (HLB, citrus greening), vectored by D. citri, was detected in Florida for the first time in Aug 2005. In Florida, the only known HLB pathogen is 'Candidatus Liberibacter asiaticus' (Las). After HLB was known to be established in Florida, the psyllid vectors found in regulatory samples from plants for sale were tested for the pathogen by real-time qPCR. Approximately 1,200 regulatory samples were tested between Aug 2005 and Aug 2009. Samples came from venues in 44 of Florida's 67 counties. Most of the samples came from citrus, but about 11% came from Murraya exotica, a popular ornamental plant and close relative of citrus. Approximately 9.7% of the psyllid samples tested were positive for Las. Numbers of samples and proportion of positive samples varied by year and by county. Diaphorina citri Kuwayama fue registrado por primera vez en la Florida en junio de 1998, y la enfermedad Huanglongbing (HLB, enverdecimiento de los cítricos) se detectó en el estado por primera vez en agosto del 2005. En Florida, el único patógeno conocido de HLB es 'Candidatus Liberibacter asiaticus' (=Las). Después de que HLB se estableció en la Florida, los vectores psílidos encontrados en las muestras de las plantas reguladas para la venta fueron probados para el patógeno en tiempo real de qPCR. Aproximadamente 1,200 muestras regulatorias fueron examinadas entre agosto del 2005 y agosto del 2009. Las muestras procedian de 44 de los 67 condados de la Florida. La mayoría de las muestras procedían de cítricos, pero aproximadamente el 11% fueron de Murraya exotica, una planta ornamental popular que se relaciona con los cítricos. Aproximadamente el 9.7% de las muestras fueron positivas para el patógeno "Las". El número de muestras y la proporción de muestras positivas variaron según el año y por condado.
A new pest of cole crops, the Bagrada bug, was recently found infesting commercial Brassica crops throughout the southwestern desert growing areas of Arizona and California. The authors anticipate that this pest will become permanently established. Development of information on the Bagrada bug's biology and ecology on our local crops will be important for developing pest management recommendations.
Accepted for publication 2 May 2010. Published 21 June 2010.
La “Huanglongbing” (enverdecimiento de los citricos) es una de las enfermedades mas sérias de los cítricos. El movimiento de la enfermedad sucede como resultado de la transmissión natural por el insect vector y por el movimiento de material de plantas infectadas. Demonstramos que Diaphorina citri Kuwayama, un vector de los patógenos del enverdecimiento de los cítricos, puede ser transportado en remolques con frutas no procesadas. Varias muestras de D. citri recolectadas de remolques de naranjas resultaron positivas para los patógenos del enverdecimiento de los cítricos, lo cual indica que la enfermedad puede esparcirce ampliamente con el movimiento de frutas maduras como resultado del traslado de los vectores. Mientras que el movimiento de la enfermedad y el vector por medio del movimiento de material de plantas en nuevas areas ha sido reconocido, nuestros hallazgos enfatizan la necesidad de evaluar la importancia del movimiento del sílido por largas distancias sobre frutas no procesadas, aun en la ausencia de tejido vegetativo.
Study of the impacts of biological invasions, a pervasive component of global change, has generated remarkable understanding of the mechanisms and consequences of the spread of introduced populations. The growing field of invasion science, poised at a crossroads where ecology, social sciences, resource management, and public perception meet, is increasingly exposed to critical scrutiny from several perspectives. Although the rate of biological invasions, elucidation of their consequences, and knowledge about mitigation are growing rapidly, the very need for invasion science is disputed. Here, we highlight recent progress in understanding invasion impacts and management, and discuss the challenges that the discipline faces in its science and interactions with society.
The systemic neonicotinoid insecticide imidacloprid, Admire Pro, was applied to 3- and 4-yr-old nonbearing 'Rio Red' grapefruit, Citrus x paradisi Macfad., trees in 2006 and 2007, respectively, to determine its effects in the control of two major citrus pests, the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), and a citrus leafminer Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae). Young flush shoots were randomly collected weekly for 13 and 11 wk in 2006 and 2007, respectively, to determine the infestation levels and densities of immature stages of both Asian citrus psyllid and P. citrella. Additional flush shoot samples were collected in 2007 and titers of imidacloprid in leaf tissue were determined using an enzyme-linked immunosorbent assay. Soil application of imidacloprid significantly reduced the infestation levels and densities of both pests on flush shoots, starting from the second week post application. The effects of the neonicotinoid insecticide were similar in both years. Analysis of imidacloprid concentration in leaf tissue showed a gradual increase during the first 3 wk, and titers remained well above 200 ppb for 11 wk postapplication. Significant positive correlations were obtained between imidacloprid titers in leaf tissue and the percentage of control levels achieved for both pests. A high level of suppression of both P. citrella and Asian citrus psyllid populations on citrus trees was associated with imidacloprid titer in leaf tissue >200 ppb, which was reached 2 wk after soil treatment. Although soil application of imidacloprid did not provide rapid knockdown of Asian citrus psyllid and P. citrella populations, it resulted in chronic residues in leaf tissue and long-term suppression of both pests.
A competitive enzyme-linked immunosorbent assay (ELISA) technique was evaluated for quantifying titers of imidacloprid in xylem fluid extracted from Vitis vinifera L. grapevines that were treated with systemic applications of the neonicotinoid insecticide Admire. Evidence of matrix effects, factors that compromise the precision and accuracy of the ELISA, was present in assays with undiluted xylem fluid. These effects could be eliminated by dilution of extracts in water, resulting in a lower sensitivity of the assay of 4 microg liter(-1). In a field trial conducted in a commercial vineyard, there was an excellent correlation between Admire application rates and xylem fluid concentrations of imidacloprid. At an Admire application rate of 1.17 liter ha(-1) (16 fl oz per acre), uptake of imidacloprid into vines was rapid. Imidacloprid was consistently detected in the xylem for up to 3 mo after application at concentrations known to be effective at managing populations of the sharpshooter Homalodisca coagulata Say, an important vector of Xylella fastidiosa Wells in California vineyards. The ELISA is a sensitive technique that can be used to study the behavior of systemic insecticides within crop systems and their impact on pest populations.
Imidacloprid, the major component of many widely used insecticide formulations, is highly persistent in soils. In this study, the sorption of imidacloprid by six soils as well as its photodegradation and hydrolysis in water were studied. The soils differed significantly in organic matter content and other physical and chemical properties. Sorption increased with increasing soil organic matter content but was not significantly correlated with other soil properties. Removal of organic matter via H2O2 oxidation decreased the sorption. By normalizing the Freundlich coefficients (Kf) to organic matter contents, the variability in obtained sorption coefficient (Kom) was substantially reduced. These results indicate that soil organic matter was the primary sorptive medium for imidacloprid. The low heat of sorption calculated from Kom suggests that partition into soil organic matter was most likely the mechanism. The photodegradation and hydrolysis of imidacloprid in water followed pseudo-first-order kinetics; however, the latter process needed a six-time-higher activation energy. While both processes produced the same main intermediate, they occurred via different pathways. The hydrolysis of imidacloprid was not catalyzed by the high interlayer pH in the presence of metal-saturated clays, which appeared to result from the lack of the pesticide adsorption in the interlayers of clays.
Background:
Studies were conducted to evaluate uptake and retention of 3 systemic neonicotinoid insecticides, dinotefuran, imidacloprid, and thiamethoxam, in potted citrus nursery plants treated at standard label rates. Infestation of these plants placed at a field site with moderate levels of Asian citrus psyllid (ACP) was monitored for 14 weeks following treatments and insecticide residues in leaf tissue were quantified using ELISA. Bioassays were conducted using leaves harvested on various dates post-treatment to compare the efficacies of residues against adult ACP.
Results:
Residues of the 3 neonicotinoids were detected in leaf tissues within 1 week after treatment. Peak concentrations established at 1 week for imidacloprid and dinotefuran and at 2 weeks for thiamethoxam. Imidacloprid and thiamethoxam outperformed the control and dinotefuran treatments at protecting trees from infestations by ACP eggs and nymphs. For a given insecticide concentration in leaf tissue, thiamethoxam induced the highest mortality of the 3 insecticides, and dinotefuran was the least toxic.
Conclusion:
If the time needed to achieve effective thresholds of a systemic neonicotinoid is known, treatments at production facilities could be scheduled that would minimize unnecessary post-treatment holding periods and ensure maximum retention of effective concentrations after the plants have shipped to retail outlets. The rapid uptake of the insecticides and retention at effective concentrations in containerized citrus suggest that the current 30-day post-treatment shipping restriction from production facilities to retail outlets outside of quarantine could be shortened to 14 days. Thiamethoxam should be added to the list of approved nursery treatments.
Levels of armored scales (Hemiptera: Diaspididae) on Mexican Hass avocados imported into California over May 2008–June 2009 were monitored on 135 trucks entering the state via the Blythe border station, the entry point receiving the highest volume of fruit. Levels of live sessile scales were 3.9-fold higher than indicated in a previous survey (September 2007–April 2008) although levels of live eggs and crawlers were similar to previous levels. A survey of avocado fruit in California infested with armored scales detected four species known to be endemic but failed to find any of the seven exotic Diaspididae entering the state on Mexican fruit. Monitoring of Mexican armored scales on imported avocados from September 2007 to December 2010 recovered 10 species of parasitoids predominated by two species of Signiphora Ashmead (Hymenoptera: Signiphoridae). One of these species, Signiphora flavopalliata Ashmead, comprised 36% of all collected Mexican parasitoids and is a known hyperparasitoid. A survey of armored scale parasitoids present on commercial California avocados detected 17 genetic signatures, with only four of these in common with those detected on imported Mexican fruit. The implications of these findings are discussed.
Sorption-desorption of imidacloprid [1-[(6-chloro-3-pyridinyl)methyl]-N-nitro-2-imidazolidinimine] and metabolites 1-[(6-chloro-3-pyridinyl)methyl]-2-imidazolidinone (imidacloprid-urea), 1-[(6-chloro-3-pyridinyl)methyl]-4,5-dihydro-1H-imidazol-2-amine (imidacloprid-guanidine), and 1-[(6-chloro-3-pyridinyl)methyl]-1H-imidazol-2-amine (imidacloprid-guanidine-olefin) in three soils was determined using the batch equilibration technique with initial concentrations for the four chemicals ranging from 0.05 to 1.5 mu g mL(-1), which corresponds to a field application rate of 0.2-1.0 kg ha(-1) Calculated slopes of the Freundlich sorption isotherms were significantly less than 1. The order of sorption (K-f) was imidacloprid-guanidine > imidacloprid-guanidine-olefin > imidacloprid > imidacloprid-urea in the three soils. Average Kf-oc values were 203, 412, 2740, and 3200 for imidacloprid-urea, imidacloprid, imidacloprid-guanidine-olefin, and imidacloprid-guanidine, respectively. Desorption was hysteretic for all chemicals in all soils. Greatest hysteresis was observed with imidacloprid-guanidine and imidacloprid-guanidine-olefin. Sorption-desorption of imidacloprid determined at half the solubility (250 mu g mL(-1)) (K-oc = 77) greatly overpredicts potential leaching compared to K-oc determined at field application rates (Kf-oc = 411).
SUMMARY A detailed account is given of the history, aetiology, biology, epidemiology, detection, geographical distribu- tion, and control of huanglongbing (HLB), a destructive disease of citrus that represents a major threat to the world citrus industry, and is slowly invading new citrus- growing areas. HLB, whose name in Chinese means "yellow dragon disease", was first reported from south- ern China in 1919 and is now known to occur in next to 40 different Asian, African, Oceanian, South and North American countries. The agent is a phloem-restricted, non cultured, Gram-negative bacterium causing crip- pling diseases denoted "greening " in South Africa, "mottle leaf" in the Philippines, "dieback" in India, "vein phloem degeneration" in Indonesia. The HLB bacterium belongs to the genus Candidatus Liberibac- ter, three species of which are currently known, Candi- datus Liberibacter asiaticus, occurring in Asian coun- tries and, to a lesser extent, in Brazil and the USA (Florida), Candidatus Liberibacter africanus with its subspecies "capensis", recorded from African countries, and Candidatus Liberibacter americanus present in Brazil. The suggestion is that each liberibacter species has evolved in the continent after which it is named. HLB symptoms are virtually the same wherever the dis- ease occurs. Infected trees show a blotchy mottle condi- tion of the leaves that results in the development of yel- low shoots, the early and very characteristic symptom of the disease. Trees are stunted, declining and bear a few, small-sized, and deformed (lop-sided) fruits, that are poorly coloured (greening) and with coloration starting at the peduncular end (colour inversion). HLB can be transmitted by grafting from citrus to citrus and by dod- der to periwinkle. The psyllids Trioza erytreae and Di- aphorina citri are natural vectors. Two different types of
The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is the most important pest of citrus worldwide because it serves as a vector of "Candidatus Liberibacter" species (Alphaproteobacteria) that cause huanglongbing (citrus greening disease). All commercially cultivated citrus is susceptible and varieties tolerant to disease expression are not yet available. Onset of disease occurs following a long latent period after inoculation, and thus the pathogen can spread widely prior to detection. Detection of the pathogen in Brazil in 2004 and Florida in 2005 catalyzed a significant increase in research on D. citri biology. Chemical control is the primary management strategy currently employed, but recently documented decreases in susceptibility of D. citri to several insecticides illustrate the need for more sustainable tools. Herein, we discuss recent advances in the understanding of D. citri biology and behavior, pathogen transmission biology, biological control, and chemical control with respect to "Candidatus Liberibacter asiaticus." Our goal is to point toward integrated and biologically relevant management of this pathosystem.
The metabolism of the chloronicotinyl insecticide imidacloprid is strongly influenced by the method of application. Whilst in foliar application most of the residues on the leaf surface display unchanged parent compound, most of the imidacloprid administered to plants by soil application or seed treatment is metabolized more or less completely, depending on plant species and time. The present study revealed that certain metabolites of imidacloprid which have been described in crop plants are highly active against aphid pests in different types of bioassays. Some of these metabolites showed a high oral activity against the green peach aphid (Myzus persicae), and the cotton aphid (Aphis gossypii). The aphicidal potency of the metabolites investigated was weaker in aphid dip tests than in oral ingestion bioassays using artificial double membranes. The most active plant metabolite was the imidazoline derivative of imidacloprid. The LC50 values of this metabolite for M. persicae and A. gossypii in oral ingestion bioassays were in the lower ppb-range, i.e. 0·0044 and 0·0068 mg litre-1, respectively. Most of the other reported metabolites showed much weaker activity. Compared to imidacloprid, the imidazoline derivative showed superior affinity to housefly (Musca domestica) head nicotinic acetylcholine receptors, while all other metabolites were less specific than imidacloprid. It seems possible that, after seed treatment or soil application, a few of the biologically active metabolites arising are acting in concert with remaining levels of the parent compound imidacloprid, thus providing good control and long-lasting residual activity against plant-sucking pests in certain crops. © 1998 SCI.
Trunk injections of systemic insecticides were evaluated for the management of avocado thrips. Insecticide residues were quantified in leaves to determine when after treatment, and for how long, toxic concentrations of the insecticides were present. Residues in fruit were quantified to determine whether trunk injection of insecticides might present a greater risk than traditional application methods for contaminating fruit.
Residues of imidacloprid and dinotefuran were at least tenfold higher in leaves when trees were treated via trunk injection compared with soil application. Dinotefuran uptake was more rapid than imidacloprid, and no residues were detected within fruit. Acephate was also mobilized very rapidly and gave good control of thrips in bioassays; however, residues of acephate and its insecticidal metabolite methamidophos were detected in the fruit for up to 4 weeks after injection. Avermectin uptake was very slow, and it was ineffective against avocado thrips.
Trunk injections of acephate and dinotefuran permitted rapid uptake into avocados, and they are strong candidates as control methods for avocado thrips. However, residues of organophosphates in fruit could necessitate increased preharvest intervals. Residues of neonicotinoids were below detection limits in fruit, suggesting that neonicotinoids may be the more suitable control option of the two chemical classes.
Linear Mixed-Effects * Theory and Computational Methods for LME Models * Structure of Grouped Data * Fitting LME Models * Extending the Basic LME Model * Nonlinear Mixed-Effects * Theory and Computational Methods for NLME Models * Fitting NLME Models
The effects due to Candidatus Liberibacter infection, commonly called citrus greening or Huanglongbing (HLB), on volatile and nonvolatile components of orange juices, OJ, were examined using GC-MS and high-performance liquid chromatography (HPLC). HLB symptomatic, asymptomatic, and control "Hamlin" and "Valencia" oranges were harvested from December to May during the 2007 to 2008 harvest season. Brix/acid levels in control and asymptomatic juices were similar but symptomatic juices were as much as 62% lower than control juices. No bitter flavanone neohesperidosides were detected and polymethoxyflavone concentrations were well below bitter taste thresholds. Limonin concentrations were significantly higher (91% to 425%) in symptomatic juice compared to control but still below juice bitterness taste thresholds. Juice terpenes, such as gamma-terpinene and alpha-terpinolene, were as much as 1320% and 62% higher in symptomatic juice than control. Average ethyl butanoate concentrations were 45% lower and average linalool was 356% higher in symptomatic Valencia OJ compared to control. Symptomatic Valencia OJ had on average only 40% the total esters, 48% the total aldehydes, and 33% as much total sesquiterpenes as control juice. Total volatiles between control and symptomatic juices were similar due to elevated levels of alcohols and terpenes in symptomatic juice. There were no consistent differences between asymptomatic and control juices. The chemical composition of juice from HLB/greening symptomatic fruit appears to mimic that of juice from less mature fruit. The reported off-flavor associated with symptomatic juices probably stem from lower concentrations of sugars, higher concentrations of acid as all known citrus bitter compounds were either below taste thresholds or absent.
Titers of two systemic neonicotinoid insecticides in citrus trees were measured in conjunction with conventional evaluations of their impact on glassy-winged sharpshooter (Homalodisca coagulata (Say); GWSS) populations. Xylem fluid samples were collected at regular intervals and from multiple locations within field-grown citrus trees to determine imidacloprid and thiamethoxam concentrations using commercial ELISA kits. Uptake profiles varied considerably with peak mean titers of imidacloprid occurring 6-8 weeks after application compared with 2 weeks for thiamethoxam. The persistence of each compound also varied as near-peak levels of imidacloprid were sustained for another 6-10 weeks before gradually declining. In contrast, thiamethoxam titers declined more rapidly after the initial peak, possibly reflecting an application rate only one-quarter of that used for imidacloprid. Within-tree distributions were more similar for the two compounds, with no significant effect due to height of the sample (upper or lower half) or to the quadrant location within the tree, with the exception of one quadrant in the thiamethoxam-treated trees. Substantial reductions in GWSS nymphs and adults were observed in imidacloprid-treated trees during the 2001 trial and were sustained for 4-5 months after treatment. Treatment effects on nymphs were not as well pronounced in the 2002 trial, when overall GWSS infestations were much reduced from the previous year. However, consistently lower adult infestations were still observed in 2002 for both treatments compared with untreated trees. Information on the spatial and temporal profiles in citrus trees was obtained for both compounds to complement field impact data and improve understanding of their pest management potential.
A competitive ELISA (enzyme-linked immunosorbent assay) technique was evaluated for quantifying titres of imidacloprid in homogenates of leaf discs sampled from avocado plants treated with systemic applications of imidacloprid 240 g litre(-1) SC (Admire). Matrix effects were evident with undiluted leaf tissue homogenates, but these were effectively eliminated by dilution of homogenates in water. In a field trial conducted in a commercial nursery, there was an excellent correlation between imidacloprid residues within leaves and avocado thrips (Scirtothrips perseae Nakahara) mortality. However, with subsequent sampling over a 2-month period, the relationship between mortality and apparent imidacloprid concentration became less robust, suggesting that the material was being degraded within the plant to non-toxic metabolites. Nevertheless, assessments of thrips mortality on leaves that had been recently treated with imidacloprid established a lower threshold of activity for imidacloprid residues of 6 ng cm(-2) leaf. Limitations on the use of ELISA to quantify the impact of systemic insecticides on pest populations are discussed.
Asian citrus psyllid host list
CDFA, 2018. Asian citrus psyllid host list. https://www.cdfa.ca.gov/plant/PDEP/target_
pest_disease_profiles/hostlists/AsianCitrusPsyllid-HostList.pdf, Accessed date: 8
January 2018.
U.S. retailers look to limit pesticides to help honeybees
- C Gillam
Gillam, C., 2014. U.S. retailers look to limit pesticides to help honeybees. https://www.
reuters.com/article/us-usa-agriculture-bees/u-s-retailers-look-to-limit-pesticides-tohelp-honeybees-idUSKBN0F02M120140625, Accessed date: 8 January 2018.
How serious is the threat of Asian citrus psyllid and huanglongbing?
- Grafton-Cardwell
Grafton-Cardwell, E.E., 2010. How serious is the threat of Asian citrus psyllid and
huanglongbing? Citrograph 1 (1), 8-10.
Biology of Horticultural Crops
- P Spiegel-Roy
- E E Goldschmidt
Spiegel-Roy, P., Goldschmidt, E.E., 1996. Biology of Horticultural Crops. Biology of
Citrus. 230pp. Cambridge University Press.
- F J Byrne
F.J. Byrne et al.
Crop Protection 109 (2018) 33-41
Application of competitive Enzyme-Linked Immunosorbent Assay for the quantification of imidacloprid titers in xylem fluid extracted from grapevines
- Byrne
Biology and management of Asian citrus psyllid, vector of the haunglongbing pathogens
- Grafton-Cardell
Incidence of huanglongbing-associated ‘Candidatus Liberibacter asiaticus’ in Diaphorina citri (Hemiptera: Psyllidae) collected from plants for sale in Florida
- Halbert