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Huanglongbing (HLB) is a bacterial infection of citrus trees transmitted by the Asian citrus psyllid Diaphorina citri . Mitigation of HLB has focused on spraying of insecticides to reduce the psyllid population and removal of trees when they first show symptoms of the disease. These interventions have been only marginally effective, because symptoms of HLB do not appear on leaves for months to years after initial infection. Limited knowledge about disease spread during the asymptomatic phase is exemplified by the heretofore unknown length of time from initial infection of newly developing cluster of young leaves, called flush, by adult psyllids until the flush become infectious. We present experimental evidence showing that young flush become infectious within 15 d after receiving an inoculum of Candidatus Liberibacter asiaticus (bacteria). Using this critical fact, we specify a microsimulation model of asymptomatic disease spread and intensity in a grove of citrus trees. We apply a range of psyllid introduction scenarios to show that entire groves can become infected with up to 12,000 psyllids per tree in less than 1 y, before most of the trees show any symptoms. We also show that intervention strategies that reduce the psyllid population by 75% during the flushing periods can delay infection of a full grove, and thereby reduce the amount of insecticide used throughout a year. This result implies that psyllid surveillance and control, using a variety of recently available technologies, should be used from the initial detection of invasion and throughout the asymptomatic period. Significance Huanglongbing (HLB) is a vector-transmitted bacterial infection of citrus trees that poses a major threat to the citrus industry in Florida, Texas, and California. Current control strategies that focus on the vector, the Asian citrus psyllid Diaphorina citri , are usually initiated when the trees become symptomatic, anywhere from 10 mo to several years after initial infection. We show, experimentally, that newly infected young leaves can become infectious within 10–15 d after receiving an inoculum of bacteria from an adult psyllid. We then show by microsimulation of the asymptomatic spread of HLB through a grove under different invasion scenarios and control strategies that reduction of up to 75% of adult psyllids and nymphs can enhance citrus production.

The citrus disease huanglongbing (HLB), associated with an uncultured bacterial pathogen, is threatening the citrus industry worldwide. A mathematical model of the transmission of HLB between its psyllid vector and citrus host has been developed to characterize the dynamics of the vector and disease development, focusing on the spread of the pathogen from flush to flush (a newly developing cluster of very young leaves on the expanding terminal end of a shoot) within a tree. This approach differs from that of prior models for vector-transmitted plant diseases where the entire plant is the unit of analysis. Dynamics of vector and host populations are simulated realistically as the flush population approaches complete infection. Model analysis indicates that vector activity is essential for initial infection but is not necessary for continued infection because infection can occur from flush to flush through internal movement in the tree. Flush production, within-tree spread, and latent period are the most important parameters influencing HLB development. The model shows that the effect of spraying of psyllids depends on time of initial spraying, frequency, and efficacy of the insecticides. Similarly, effects of removal of symptomatic flush depend on the frequency of removal and the time of initiation of this practice since the start of the epidemic. Within-tree resistance to spread, possibly affected by inherent or induced resistance, is a major factor affecting epidemic development, supporting the notion that alternate routes of transmission besides that by the vector can be important for epidemic development.

An effective surveillance method for invasive insect pests is critical for timely detection and management. This study explores the effectiveness of eight active sampling methods for detecting the presence of the two-spot cotton leafhopper ( (Ishida) (Hemiptera: Cicadellidae)), a newly emerging adventive pest in the U.S.A. that is causing economic losses in cotton and okra. We conducted field studies to compare aspirating, bagging, beat sheet, sweep netting, and four tray-based methods: a dry tray, or a tray with 70% isopropyl alcohol, tap water, or soapy water. While aspirating and bagging served as adequate sampling methods, we found that sampling with a tray containing 70% isopropyl alcohol proved to be the most effective and time-efficient approach. This method consistently enabled rapid detection of adult male specimens across both low- and high-population field sites, facilitating reliable morphological identification.

Citrus huanglongbing (HLB) is a severe problem for citrus cultivation. The disease management programs benefit from improved field tools suitable for surveying the ACP vector (Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae)) and the associated pathogen. In the present study, we utilize three-dimensional (3D) printers and design tools to develop traps that can capture and preserve ACPs. Three novel, 3D-printed traps were designed and evaluated: stem trap, and cylinder traps 1 and 2. The traps and yellow sticky cards were deployed weekly for 8 months in 2 non-commercial citrus groves in Florida; in California, the traps were evaluated for 12 months in field cages and 4 citrus groves. The stem traps captured lower numbers of ACPs at all experimental sites compared to the cylinder traps. Capture rates in the cylinder traps were comparable to the sticky trap, making the device a viable tool for monitoring field ACPs. The two main advantages of using the reusable 3D traps over standard methods of ACP and HLB surveys include dynamic sampling that can be conducted year-round and the capture of ACPs that can be preserved and tested. Improved trapping may facilitate quick management decisions and mitigate HLB.

Melaleuca quinquenervia (Cav.) S.T. Blake (Myrtales: Myrtaceae) is an invasive tree in Florida, USA, for which a psyllid, Boreioglycaspis melaleucae (Moore) (Hemiptera: Aphalaridae), was successfully established in April, 2002 to control its spread. A parasitoid wasp, Psyllaephagus migrator McClelland, sp. nov. was found to parasitize this psyllid in Australia, which we consider to be its native range, and in Florida, where we consider it to be adventive. We provide a description, high resolution images and morphological diagnosis for P. migrator and a molecular data set of five gene regions to facilitate its identification and use in phylogenetic studies. The biology of the parasitoid is presented with documentation of its immature stages. Trapping data suggest that P. migrator has reduced populations of the biocontrol agent B. melaleucae in Florida.

Invasive insects threaten ecosystem stability, public health, and food security. Documenting newly invasive species and understanding how they reach into new territories, establish populations, and interact with other species remain vitally important. Here, we report on the invasion of the South American leafhopper, Curtara insularis into Africa, where it has established populations in Ghana, encroaching inland at least 350 km off the coast. Importantly, 80% of the specimens collected were intercepted between 160 and 190 m above ground. Further, the fraction of this species among all insects collected was also higher at altitude, demonstrating its propensity to engage in high-altitude windborne dispersal. Its aerial densities at altitude translate into millions of migrants/km over a year, representing massive propagule pressure. Given the predominant south-westerly winds, these sightings suggest an introduction of C. insularis into at least one of the Gulf of Guinea ports. To assess the contribution of windborne dispersal to its spread in a new territory, we examine records of C. insularis range-expansion in the USA. Reported first in 2004 from central Florida, it reached north Florida (Panhandle) by 2008–2011 and subsequently spread across the southeastern and south-central US. Its expansion fits a “diffusion-like” process with 200—300 km long “annual displacement steps”—a pattern consistent with autonomous dispersal rather than vehicular transport. Most “steps” are consistent with common wind trajectories from the nearest documented population, assuming 2—8 hours of wind-assisted flight at altitude. Curtara insularis has been intercepted at US ports and on trucks. Thus, it uses multiple dispersal modalities, yet its rapid overland spread is better explained by its massive propagule pressure linked with its high-altitude windborne dispersal. We propose that high-altitude windborne dispersal is common yet under-appreciated in invasive insect species.

Two approaches to correlative species distribution models (MaxEnt and Multi-Model Framework) were used to predict global and local potential distribution of huanglongbing (HLB) caused by Candidatus Liberibacter asiaticus ( C Las) and its vector the Asian citrus psyllid (ACP, Diaphorina citri Kuwayama). Long-term climate data were sourced from the Worldclim website. The global distribution of C Las and ACP was gathered from online databases, literature review and communication with specialists. Data on C las and ACP distribution in the USA were not used in model calibration to allow model validation for independent locations. Both models successfully predicted Florida and coastal areas in the Gulf Coast states as highly suitable for C las and ACP. The models also predicted that coastal areas in California were climatologically favorable for ACP and C las, but less so than in Florida. When current USA presence data were included in the models, the suitable areas for ACP establishment expanded to the Central Valley, CA, while this area remained less conducive for C Las. Climate suitability was primarily related to rainfall and secondarily to temperature. Globally, both models predicted that climates in large areas of Africa, Latin America and North Australia were highly suitable for ACP and C Las, while the climate in the Mediterranean area was moderately suitable for ACP but less suitable for C Las, except for that in southern Portugal and Spain. C las predictions from our models could be informative for countries like Australia, New Zealand, citrus-producing European countries and much of Africa, where C Las and D. citri have not been reported.

Cacopsylla pyricola (Förster) (Hemiptera: Psyllidae) is the most expensive and challenging insect pest of commercial pear trees in the Pacific Northwest. Integrated pest management (IPM) programs are working toward relying more heavily on natural enemies to reduce insecticide use. Trechnites insidiosus (Crawford) (Hymenoptera: Encyrtidae) is the main parasitoid of C. pyricola, but little is known about its biology in the region. Developing sampling tools is important for the deployment of IPM programs, including monitoring of natural enemies. In this study, we examined 2 conventional monitoring methods: beat trays and yellow sticky cards, in addition to screened sticky cards and 3D-printed cylinder traps. Additionally, we tested an overwintering trap for the collection of parasitized C. pyricola.The trapping methods were tested in orchards in Oregon and Washington. Unscreened cards caught the most T. insidiosus and C. pyricola, followed by screened cards, cylinder traps, and then beat trays. Beat trays sometimes failed to catch any T. insidiosus, even when it was found in abundance via other methods. Screened cards and cylinder traps reduced bycatch and increased ease of identifying T. insidiosus. Specimens from the cylinder traps were also more suitable for use in molecular analysis. The overwintering traps were effective at capturing parasitized C. pyricola, but were highly variable year to year. The ideal trapping method will vary based on research needs (e.g., DNA preservation, reducing bycatch, catching higher numbers), but both screened sticky cards and cylinder traps were viable methods for monitoring T. insidiosus and its host.

Citrus surveys were conducted at high (>700 m), medium (300-600 m) and low (<200 m) altitudes in Tanzania in 2014/15. Adults and nymphs of Trioza erytreae (del Guercio) were abundant in the highlands and less abundant at medium altitudes. Unexpectedly, adults and nymphs of Diaphorina citri Kuwayama, the Asian citrus psyllid, were found and collected at medium altitudes, around Morogoro. No psyllids were observed at low altitudes. Severe huanglongbing symptoms and tree decline were evident at high altitudes, while mild and few symptoms were observed at intermediate and low altitudes, respectively. DNA was extracted from leaf and psyllid samples and subjected to conventional PCR (cPCR) with seven different primer sets and RT qPCR with two primer sets. cPCR bands were sequenced and subjected to phylogenetic analysis. Candidatus Liberibacter africanus (Laf) was detected in highland leaf and T. erytreae samples from high and medium altitudes by all methods. Sequences from leaves and psyllids were similar to those from South Africa. Candidatus Liberibacter asiaticus (Las) was detected by qPCR in medium altitude leaf samples, but cross-reaction with Laf was likely because presence of Las was not confirmed by cPCR and sequencing. Neither Laf nor Las were detected in D. citri samples. This is the first reported occurrence of D. citri in Africa. Predictions were made of the potential distribution of D. citri and Las in Africa and along the Mediterranean coast using the correlative models MAXENT and Multi-Model Framework. Additional surveys at medium and low altitudes and quarantine measures are recommended.

Melaleuca quinquenervia (Cav.) S.T. Blake (Myrtales: Myrtaceae) is an invasive tree in Florida, USA, for which a psyllid, Boreioglycaspis melaleucae (Moore) (Hemiptera: Aphalaridae), was successfully established in April, 2002 to control its spread. A parasitoid wasp, Psyllaephagus migrator McClelland, sp. nov. was found to parasitize this psyllid in Australia, which we consider to be its native range, and in Florida, where we consider it to be adventive. We provide a description, high resolution images and morphological diagnosis for P. migrator and a molecular data set of five gene regions to facilitate its identification and use in phylogenetic studies. The biology of the parasitoid is presented with documentation of its immature stages. Trapping data suggest that P. migrator has reduced populations of the biocontrol agent B. melaleucae in Florida.