Plant volatiles and density-dependent conspecific female odors are used by Asian citrus psyllid to evaluate host suitability on a spatial scale

We investigated how chemical cues derived from female Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae) and their host plants affect host acceptance choices by conspecifics. In four-choice cage and two-choice olfactometer assays, female psyllids avoided conspecific female cues in a density-dependent manner. However, odors from citrus plants actively damaged by psyllid feeding were attractive to conspecific females. When odors from feeding-damaged plants were presented simultaneously with odors from female D. citri, attraction of female conspecifics was no longer observed as compared with a clean air control in olfactometer assays. In subsequent experiments, D. citri females were released within arenas that contained actively feeding-damaged or non-damaged (control) citrus plants, each with previously psyllid-infested and uninfested young leaves. D. citri development is linked to the presence of these newly emerging leaves which is the only site of nymphal development. Female D. citri were initially attracted by the actively damaged plants as compared with non-damaged controls. After acceptance of plants that were actively damaged by feeding, D. citri females preferentially chose and settled on uninfested young leaves as compared with previously infested young leaves. A herbivore-induced plant volatile attractant and a female-specific odor repellent appear to be complementary foraging cues providing psyllids with information at two spatial scales: (1) the whole plant level for choosing a plant potentially harboring male conspecifics for mating, and (2) the within plant level to reduce intra-conspecific competition by identifying previously exploited resources.     

Diurnal Patterns of Flight Activity and Effects of Light on Host Finding Behavior of the Asian Citrus Psyllid

The Asian citrus psyllid, Diaphorina citri (Hemiptera: Psyllidae), is an invasive pest of citrus in the United States. The psyllid feeds and reproduces primarily on new flush growth of citrus and other rutaceous plants. Because it vectors the bacterial causal agents of the deadly citrus greening disease, D. citri is potentially a pest of economic importance in all citrus growing areas where it occurs together with the disease. We investigated the diurnal patterns of its flight activity in the field and the effects of light on its host selection and egg laying behaviors. The numbers of adult psyllids caught on yellow sticky traps were 3 to 4-fold higher during daytime than nighttime. Daytime flight activity of D. citri adults also varied with time of the day with peak catches occurring at midday from 1200 to 1500 h. Illumination of the traps at night increased their attractiveness to adult psyllids by 5-fold. Similarly, light significantly increased plant colonization by adults and female egg deposition on potted plants in the laboratory. These results showed that the flight activity and host selection behavior of adult psyllids are regulated by light and circadian rhythms. Thus, adult psyllids utilize light as visual cues in their host-plant selection process.     

Isolation and characterization of an Isaria fumosorosea isolate infecting the Asian citrus psyllid in Florida

A fungal pathogen that killed adult Diaphorina citri Kuwayama (Asian citrus psyllid) (Hemiptera: Psyllidae) in Florida citrus groves during the fall of 2005 was identified and characterized. Investigation of this pathogen is important because D. citri vectors citrus greening disease (Huanglongbing), which was reported in Florida in 2005. The morphological and genetic data generated herein support identification of the fungus as Isaria fumosorosea Wize (Ifr) (=Paecilomyces fumosoroseus) (Hypocreales: Cordycipitaceae) from the Asian citrus psyllid (Ifr AsCP). Koch’s postulates were fulfilled after the fungus was isolated in vitro and transmitted to healthy psyllids, which then exhibited a diseased-phenotype similar to that observed in the field. Both in vitro growth characteristics and two Ifr AsCP-specific molecular markers discriminated the psyllid pathogen from another local Ifr isolate, Ifr 97 Apopka. These molecular markers will be useful to track the dynamics of this disease in D. citri populations. The potential for utilizing Ifr to complement existing psyllid pest management strategies is discussed.     

Morphological and molecular characterization of a Hirsutella species infecting the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), in Florida

The Asian citrus psyllid, Diaphorina citri Kuwayama, is an invasive pest that vectors citrus greening disease, which recently was detected in Florida. Mycosed adult D. citri were collected at four sites in central Florida between September 2005 and February 2006. Observation of the cadavers using scanning electron microscopy revealed that the pathogen had branched synnemata supporting monophiladic conidiogenous cells. A high-fidelity polymerase chain reaction (PCR) assay was used to amplify the 18S rRNA, 28S rRNA and beta-tubulin genes of the pathogen for phylogenetic analysis. The morphological and genetic data indicated that the pathogen was a novel isolate related to Hirsutella citriformis Speare. PCR assays using isolate-specific primers designed from the unique putative intron region of the beta-tubulin sequence distinguished the psyllid pathogen from five related Hirsutella species. The pathogen was maintained in vivo by exposing healthy D. citri to the synnemata borne on field-collected cadavers. Infected psyllids had an abundance of septate hyphal bodies in their hemolymph and exhibited behavioral symptoms of disease. In vitro cultures of the pathogen were slow-growing and produced synnemata similar to those found on mycosed D. citri. In laboratory bioassays, high levels of mortality were observed in D. citri that were exposed to the conidia-bearing synnemata produced in vivo and in vitro.     

Evaluation of Isaria fumosorosea (Hypocreales: Cordycipitaceae) for control of the Asian citrus psyllid,Diaphorina citri (Hemiptera: Psyllidae)

A laboratory bioassay was developed to evaluate strains of Isaria fumosorosea Wize, against Diaphorina citri. Up to 100% of adult psyllids were killed at concentrations between 10⁶ and 10⁷ blastospores/ml after 12 days, with derived LC₅₀ values (at 7 days post treatment) between 1.4 × 10⁵ and 2.0 × 10⁶ blastospores/ml for strains ARSEF 3581, FE 9901 and Apopka-97. A significantly higher value (1.5 × 10⁷) was obtained with a conidial formulation of Apopka-97. Average survival times were dosage dependent, i.e. between 10.2 days at 10³ blastospores/ml and 3.5 days at 10⁸ blastospores/ml. Rates of mycosis were also dosage dependent, with up to 100% sporulation on cadavers at 10⁸ blastospores/ml but declining at lower concentrations. The Apopka-97 strain (commercially available as PFR-97) was tested against established D. citri infestations in potted citrus in greenhouse cages. Treatments at label rates reduced psyllid populations by approximately 50% over 3 weeks. The combination of PFR-97 with emulsifiable oils (0.25% v/v) did not increase psyllid mortality compared with either agent alone. Imidacloprid applied as a drench killed 100% of psyllids within 3 weeks. Subsequent greenhouse tests during humid conditions were hampered by natural dissemination of I. fumosorosea to untreated psyllids, suggesting that this fungus is spread by air movement and may be highly effective under very humid conditions. In later tests, a Cladosporium sp. rapidly colonised psyllid cadavers and leaf surfaces, but was not pathogenic in laboratory tests. Our studies confirm the potential of I. fumosorosea to be used in IPM strategies for D. citri that rely on other tactics, such as insecticidal oils and native or introduced biological control agents.     

Sex‐specific responses of Asian citrus psyllid to volatiles of conspecific and host‐plant origin

Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is the primary vector of Candidatus Liberibacter spp. bacteria that cause citrus greening, a disease of worldwide importance. Olfactometry was employed to test responses of D. citri to odours from intact citrus plants (Mexican lime, Citrus aurantifolia, sour orange, Citrus aurantium, Marsh grapefruit, Citrus paradisi and Valencia orange, Citrus sinensis), citrus plants previously infested with D. citri, and odours of conspecifics including nymphs, adult insects of same and opposite sex, and their products (honeydew), both alone and in combination. In contrast to other studies, psyllids of both sexes were attracted to volatiles of undamaged Mexican lime leaves, whereas undamaged grapefruit attracted only females, and leaves of Valencia and sour orange did not attract either sex. All four plant species attracted female psyllids when previously infested, but only Mexican lime and sour orange‐attracted males. Thus, Citrus species appear to vary in the production of both constituitive and induced volatiles that attract adult psyllids. Volatiles emitted by nymphs did not attract either sex, but psyllid honeydew was attractive to males, likely due to female pheromone residues. Males oriented to the odour of females, whereas the reverse was not true, and neither males nor females oriented to same‐sex volatiles. The addition of conspecific cues (adults, nymphs or honeydew) did not increase female attraction to previously infested leaves, but male response was increased by the presence of adults and honeydew, regardless of plant species. Thus, female psyllids appear to orient more strongly to volatiles of plant origin, whereas males respond more strongly to cues emanating from females and conspecific excretions. These results suggest that female psyllids drive the initial colonization of host plants, whereas males orient to females and infested plants. Identification of the specific volatiles involved may permit their use in monitoring and management of this pest.     

Infection of an Insect Vector with a Bacterial Plant Pathogen Increases Its Propensity for Dispersal

The spread of vector-transmitted pathogens relies on complex interactions between host, vector and pathogen. In sessile plant pathosystems, the spread of a pathogen highly depends on the movement and mobility of the vector. However, questions remain as to whether and how pathogen-induced vector manipulations may affect the spread of a plant pathogen. Here we report for the first time that infection with a bacterial plant pathogen increases the probability of vector dispersal, and that such movement of vectors is likely manipulated by a bacterial plant pathogen. We investigated how Candidatus Liberibacter asiaticus (CLas) affects dispersal behavior, flight capacity, and the sexual attraction of its vector, the Asian citrus psyllid (Diaphorina citri Kuwayama). CLas is the putative causal agent of huanglongbing (HLB), which is a disease that threatens the viability of commercial citrus production worldwide. When D. citri developed on CLas-infected plants, short distance dispersal of male D. citri was greater compared to counterparts reared on uninfected plants. Flight by CLas-infected D. citri was initiated earlier and long flight events were more common than by uninfected psyllids, as measured by a flight mill apparatus. Additionally, CLas titers were higher among psyllids that performed long flights than psyllid that performed short flights. Finally, attractiveness of female D. citri that developed on infected plants to male conspecifics increased proportionally with increasing CLas bacterial titers measured within female psyllids. Our study indicates that the phytopathogen, CLas, may manipulate movement and mate selection behavior of their vectors, which is a possible evolved mechanism to promote their own spread. These results have global implications for both current HLB models of disease spread and control strategies.     

Susceptibility of Asian citrus psyllid, <Emphasis Type="Italic">Diaphorina citri</Emphasis> (Hemiptera: Liviidae), to the insecticide afidopyropen: a new and potent modulator of insect transient receptor potential channels

A relatively new insecticide chemistry for controlling sucking insects, afidopyropen, was investigated for toxicity against Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae). We evaluated the mortality of D. citri eggs, nymphs, and adults treated with afidopyropen using both laboratory-reared and field populations. We also quantified the effects of sublethal doses of afidopyropen on D. citri feeding, host choice selection, and fecundity. For laboratory susceptible adults, the contact LC₅₀, topical application LD₅₀, and leaf dip LC₅₀ were 2.13, 2.00, and 3.08 ng/µL, respectively. For adults collected from a commercially managed citrus grove in Florida, the contact LC₅₀, topical application LD₅₀, and leaf dip LC₅₀ were 1.37, 1.92, and 4.89 ng/µL, respectively. Egg hatch was significantly reduced following exposure to afidopyropen at 100 ng/µL. Furthermore, afidopyropen reduced D. citri nymph survival and adult emergence at concentrations ranging between 0.01 and 100 ng/µL. Diaphorina citri adult feeding decreased on citrus leaves treated with afidopyropen in a concentration-dependent manner as measured indirectly by honeydew excretion, and appeared almost completely inhibited after treatment with 10 and 100 ng/µL solutions of afidopyropen. In choice tests, significantly fewer D. citri adults settled on afidopyropen-treated plants than on control plants at 24, 48, and 72 h after release, with no differences in settling between males and females. Afidopyropen reduced the fecundity of D. citri in a concentration-dependent manner. Collectively, the results suggest that afidopyropen could contribute to the integrated management of D. citri and may therefore be useful in rotational programs to improve resistance management.     

Induced Release of a Plant-Defense Volatile ‘Deceptively’ Attracts Insect Vectors to Plants Infected with a Bacterial Pathogen

Transmission of plant pathogens by insect vectors is a complex biological process involving interactions between the plant, insect, and pathogen. Pathogen-induced plant responses can include changes in volatile and nonvolatile secondary metabolites as well as major plant nutrients. Experiments were conducted to understand how a plant pathogenic bacterium, Candidatus Liberibacter asiaticus (Las), affects host preference behavior of its psyllid (Diaphorina citri Kuwayama) vector. D. citri were attracted to volatiles from pathogen-infected plants more than to those from non-infected counterparts. Las-infected plants were more attractive to D. citri adults than non-infected plants initially; however after feeding, psyllids subsequently dispersed to non-infected rather than infected plants as their preferred settling point. Experiments with Las-infected and non-infected plants under complete darkness yielded similar results to those recorded under light. The behavior of psyllids in response to infected versus non-infected plants was not influenced by whether or not they were carriers of the pathogen. Quantification of volatile release from non-infected and infected plants supported the hypothesis that odorants mediate psyllid preference. Significantly more methyl salicylate, yet less methyl anthranilate and D-limonene, was released by infected than non-infected plants. Methyl salicylate was attractive to psyllids, while methyl anthranilate did not affect their behavior. Feeding on citrus by D. citri adults also induced release of methyl salicylate, suggesting that it may be a cue revealing location of conspecifics on host plants. Infected plants were characterized by lower levels of nitrogen, phosphorus, sulfur, zinc, and iron, as well as, higher levels of potassium and boron than non-infected plants. Collectively, our results suggest that host selection behavior of D. citri may be modified by bacterial infection of plants, which alters release of specific headspace volatiles and plant nutritional contents. Furthermore, we show in a laboratory setting that this apparent pathogen-mediated manipulation of vector behavior may facilitate pathogen spread.     

Trail Chemicals of the Convergens Ladybird Beetle, <Emphasis Type="Italic">Hippodamia convergens</Emphasis>, Reduce Feeding and Oviposition by <Emphasis Type="Italic">Diaphorina citri</Emphasis> (Hemiptera: Psyllidae) on Citrus Plants

We investigated feeding and oviposition behavior of the Asian citrus psyllid, Diaphorina citri, when exposed to the foraging trails of the convergens ladybird beetle, Hippodamia convergens. Diaphorina citri females feeding on citrus leaves directly exposed to the ladybird adults or treated with trail extract excreted significantly less honeydew droplets than controls. The trail chemicals of the ladybird beetle also decreased oviposition by D. citri females on citrus. In a no-choice experiment, D. citri females preferred to oviposit on control flush and plants than those with ladybird trail-extract treatments. In two-choice experiments, 68.0% of D. citri released into cages exhibited strong selection preference for settling and eventual oviposition on control plants than plants treated with ladybird trail extract. Diaphorina citri eggs were found on all new leaf flush of control plants, whereas only 29.5% of flush on treatment plants were selected for oviposition. The trail chemical deposited by the convergens ladybird beetle elicits repellency of D. citri feeding and oviposition. Therefore, the trail chemicals my contain components that could be useful for behavior-based management of D. citri and HLB disease by reducing psyllid feeding and oviposition.     

Curry leaf smells better than citrus to females of <Emphasis Type="Italic">Diaphorina citri</Emphasis> (Hemiptera: Liviidae)

The Asian citrus psyllid (ACP) Diaphorina citri Kuwayama has a host range of about 20 species of the family Rutaceae, including Citrus spp. However, few studies have reported on its host preference. This study evaluated the host-choice behavior of ACP in curry leaf (Murraya koenigii L.), through free-choice test and bioassays with a type ‘Y’ olfactometer, and also characterized the volatiles involved in attracting the ACP. In the free-choice test, the number of adults per plant on curry leaf was higher than the number on citrus plants. When the ACP was tested in the olfactometer, the females showed preference for curry leaf over citrus plants. Sixteen volatile compounds were identified in citrus and curry leaves. Qualitative and quantitative differences in the compounds released by citrus and curry leaves were determined. The volatiles present in these hosts may play an important role in the attraction of D. citri. With this information, further studies should be done to develop new management strategies for the ACP.     

Monitoring methods for Diaphorina citri Kuwayama (Hemiptera: Liviidae) on citrus groves with different insecticide application programmes

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), is a major citrus pest that transmits the bacteria Candidatus Liberibacter asiaticus and Ca. L. americanus associated with huanglongbing (HLB) disease. Diaphorina citri population densities can affect the effectiveness of its monitoring and sampling methods. Thus, we compared different methods for adult D. citri monitoring in groves with and without insecticide application programmes. Four short‐term experiments were carried out, each one lasting four consecutive weeks. In these experiments, sticky cards with different colours (yellow, light green, green and dark green), sweep net, two suction device models, visual inspection and stem tap sampling were assessed. Two long‐term experiments were conducted for 4.5 and 5 years, in which only yellow sticky card and visual inspection for D. citri monitoring were assessed. For the short‐term experiments, psyllids were detected by all monitoring methods during all sampling periods in areas without chemical control. However, in areas with psyllid control via fortnightly and monthly applications of insecticides, only sticky cards, regardless of their colour, were able to detect the presence of D. citri. Similarly, for the long‐term experiments, yellow sticky cards were more effective than visual inspection for detecting and quantifying D. citri in all areas with or without insecticide application. Therefore, in areas where HLB is present and chemical control of psyllid is required, sticky cards are the most reliable option for monitoring D. citri.     

Effects of the fungus Isaria fumosorosea (Hypocreales: Cordycipitaceae) on reduced feeding and mortality of the Asian citrus psyllid,Diaphorina citri (Hemiptera: Psyllidae)

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is an important citrus pest primarily because it transmits bacteria putatively responsible for huanglongbing, a serious disease of citrus. We present a study on the effects of blastospore and conidial formulations of Isaria fumosorosea Wize on feeding rates and mortality of adult psyllids in laboratory bioassays. Information on quantities of honeydew droplets was used to make inferences on feeding rates. Psyllids treated with the blastospore formulation of I. fumosorosea produced fewer honeydew droplets compared to the conidial treatment and control beginning within the first 24 h after treatment. The highest daily mean number of droplets thereafter never exceeded 2.4 drops compared to 4 and 8 for the conidial treatment and control, respectively. The mean number (±SEM) of honeydew droplets produced per psyllid per day over 7 days was significantly higher in the control (5.5±0.5) compared to the blastospore treatment; however, there were no significant differences between the treatments. Psyllids treated with the conidial formulation of the pathogen showed no significant reduction in feeding activity until 4 days after treatment. One and 2 day's post-exposure, mortality of psyllids in the blastospore treatment ranged from 8 to 25% compared to 0% in the conidial and control treatments. By 7 days post-exposure, psyllid mortality reached 100% under both fungal treatments compared to none in the controls. This study documented that adult psyllids infected by I. fumosorosea (PFR 97) produce less honeydew than healthy psyllids and suggests that they may feed less, which could potentially reduce the spread of huanglongbing.     

Factors associated with Diaphorina citri immigration into commercial citrus orchards in São Paulo State,Brazil

Seasonality often influences multiple aspects of vector-borne plant diseases. With respect to the management of plant disease vectors, an understanding of the factors driving seasonal changes in vector flight activity may improve management outcomes by facilitating more proactive application of control measures. One of the most challenging issues for citrus Huanglongbing management is to forecast when disease primary spread by bacteriliferous Diaphorina citri will occur. We monitored the temporal patterns of immigrating psyllids, using upwards of 1,200 traps spread among 9 citrus farms and checked on a weekly basis over 4 years. This dataset was analysed with a set of hierarchical models to estimate the effect of climatic variables on citrus foliage production (i.e. flush), and effects of climatic variables and citrus foliage dynamics on D. citri catches over the season. The results showed substantial seasonal variability in immigrating D. citri abundance, with the critical dispersal/migration period occurring between end of winter and spring. During this period, 65% of the total psyllids were collected on sticky traps. Seasonality of immigrating D. citri coincided with changes in certain climate variables, with negative effects of humidity and daily maximum temperatures, and a positive effect of rainfall amount in prior weeks. Maximum temperature and both daily minimum temperature and rainfall during prior weeks were also associated with new citrus flush production, which itself was positively related to immigrating D. citri abundance. Based on these results, citrus growers should be aware and intensify the frequency of psyllid control tactics (i.e. insecticide and/or kaolin sprays) during this period in order to prevent Ca. L. asiaticus transmission. These results are an important step towards developing the predictive framework needed to refine D. citri and huanglongbing management.     

A field study investigating the insecticidal efficacy against Diaphorina citri Kuwayama on Kinnow mandarin,Citrus reticulata Blanco trees

Asian citrus psyllid is a most damaging insect pest of citrus. In this field study, the efficacy of seven insecticides (emamectin benzoate, bifenthrin, chlorfenapyr, fipronil, imidacloprid, pyriproxyfen and thiamethoxam) was evaluated against Diaphorina citri Kuwayama in the citrus orchard of Kinnow mandarin, Citrus reticulata Blanco. The insecticides revealed a differential and substantial relative efficacy against D. citri compared to the untreated plants. The insecticidal effect attributed as percent reduction in insect population was more prominent after three days of spray: highest reduction values were recorded with thiamethoxam (50.89%), imidacloprid (44.27%) and bifenthrin (42.94%) after first spray, and thiamethoxam (83.36%), imidacloprid (73.20%) and bifenthrin (72.66%) after second spray. Thus, neonicotinoids (thiamethoxam and imidacloprid) and pyrethroid (bifenthrin) resulted as highly effective against D. citri at three days after both sprays. At seven days, imidacloprid (63.53%) and fipronil (62.47%) presented relatively higher population reduction after first spray, and thiamethoxam (92.66%) and chlorfenapyr (89.59%) after second spray. At 12 days, the insecticidal effect on insect population became significantly at par after each spray except chlorfenapyr that reflected high population reduction (93.17%) only after second spray. It is also obvious from the data that there is need of regular monitoring to suppress the psyllids population below threshold level by timely application of the second insecticidal spray.     

Behavioral Plasticity in Probing by <Emphasis Type="Italic">Diaphorina citri</Emphasis> (Hemiptera,Liviidae): Ingestion from Phloem Versus Xylem is Influenced by Leaf Age and Surface

Diaphorina citri is a major pest of citrus because it transmits Candidatus Liberibacter asiaticus, a phloem-limited bacterium that putatively causes Huanglongbing (HLB). The disease moves slowly through a tree, and the vector facilitates further within-tree movement via transmission of the pathogen. However, this only happens when D. citri stylets contact the phloem, to inoculate bacteria during phloem salivation and acquire bacteria during phloem sap ingestion. Behavioral changes in D. citri associated with different plant parts would affect how long it takes to reach phloem and how long the psyllids stays in phloem to ingest, thereby influencing the risk of disease spread. D. citri feeding was recorded on the abaxial and adaxial surfaces of mature and immature citrus leaves. Adults in the field can be found on these surfaces at all times of year. On abaxial surface of immature leaves, phloem salivation would occur after 11 h on average, but rarely as soon as 0.56 h. The corresponding values on mature leaves were 16 and 2.7. In general, psyllids spent more time ingesting phloem sap on immature leaves than on mature leaves. Psyllids on abaxial surfaces spent more time ingesting from phloem, though the strength of this effect was less than for immature versus mature leaves. In contrast, xylem ingestion increased on mature leaves compared with young. The biological differences that could produce this outcome are discussed. The results discussed herein are of relevance to further studies on the efficacy of an insecticide to act quickly enough to prevent pathogen transmission.     

Suitability of native North American Rutaceae to serve as host plants for the Asian citrus psyllid (Hemiptera: Liviidae)

The Asian citrus psyllid, Diaphorina citri Kuwayama, a vector of citrus huanglongbing, is now present in all citrus‐producing states in the USA and Mexico. In addition to citrus, the insect can reproduce on several other plant species in the Rutaceae family; orange jasmine (Murraya spp.) and curry leaf (Bergera koenigii) are among its preferred hosts. There are several indigenous Rutaceae species in North America, and some are popular ornamentals. A study was therefore initiated to determine the suitability of some of these plants for feeding and development of the psyllid in choice and no‐choice experiments. D. citri was found to reproduce successfully on Choisya ternata, C. arizonica and Helietta parvifolia in no‐choice tests, but preferentially selected orange jasmine and curry leaf for feeding and reproduction, in choice tests. On Amyris madrensis, A. texana and Zanthoxylum fagara, adult psyllids laid eggs which hatched, but no successful nymphal development was recorded beyond the first instars. No oviposition was recorded on Esenbeckia berlandieri, Ptelea trifoliata and Casimiroa tetrameria, although adult psyllids were able to survive on these species for several days. Results showed that C. ternata, C. arizonica and H. parvifolia can serve host plants of D. citri and this constitutes the first report of these plants serving as host for D. citri. The findings of the present study suggest that native rutaceous host plants can serve as host plants and thus affect D. citri population dynamics and the epidemiology of Huanglongbing, the deadly citrus greening disease whose pathogen is vectored by D. citri. Thus, area‐wide management of this pest also should target these riparian habitats where these host plants are present with D. citri biological control agents for sustainable management of this pest.     

Effects of different temperature regimes on survival of Diaphorina citri and its endosymbiotic bacterial communities

The Asian citrus psyllid, Diaphorina citri, is a major pest of citrus and vector of citrus greening (huanglongbing) in Asian. In our field‐collected psyllid samples, we discovered that Fuzhou (China) and Faisalabad (Pakistan), populations harbored an obligate primary endosymbiont Candidatus Carsonella (gen. nov.) with a single species, Candidatus Carsonella ruddii (sp. nov.) and a secondary endosymbiont, Wolbachia surface proteins (WSP) which are intracellular endosymbionts residing in the bacteriomes. Responses of these symbionts to different temperatures were examined and their host survival assessed. Diagnostic PCR assays showed that the endosymbionts infection rates were not significantly reduced in both D. citri populations after 24 h exposure to cold or heat treatments. Although quantitative PCR assays showed significant reduction of WSP relative densities at 40°C for 24 h, a substantial decrease occurred as the exposure duration increased beyond 3 days. Under the same temperature regimes, Ca. C. ruddii density was initially less affected during the first exposure day, but rapidly reduced at 3–5 days compared to WSP. However, the mortality of the psyllids increased rapidly as exposure time to heat treatment increased. The responses of the two symbionts to unfavorable temperature regimes highlight the complex host‐symbionts interactions between D. citri and its associated endosymbionts.     

Temporal response and attraction of Diaphorina citri to visual stimuli

As the vector of the global disease of citrus greening or huanglongbing, Asian citrus pysllids, Diaphorina citri Kuwayama (Hemiptera: Liviidae), are the greatest threat to the worldwide citrus industry. Critical to management of D. citri and huanglongbing is optimization of surveillance methodologies. Although phytophagous insects may find host plants by multimodal cues, some appear to primarily use visual cues. In this study, we examined the behavior of Asian citrus psyllids toward light from light‐emitting diodes (LEDs) in the insect visible spectrum. The periodicity of attraction of psyllids to visual cues was evaluated in the field (yellow sticky traps) and laboratory (multi‐colored LEDs) with a strong peak of activity during the afternoon in both the field and the laboratory (both 14:00 to 18:00 hours). In laboratory evaluations of psyllids to differently colored LEDs, strongest attraction was to LEDs emitting ultraviolet (390 nm), green (525 nm), and yellow (590 nm) light. Male and female psyllids did not differ significantly in their responses to visual cues. These findings provide the basis for formulating better traps that reflect UV and yellow light and potentially incorporate UV LEDs for monitoring psyllids and a better understanding of Asian citrus psyllid visual behavior.     

Isolation and characterization of two entomopathogenic fungi attackingDiaphorina citri (Homoptera, Psylloidea) in Indonesia

In an attempt to suppress the propagation of citrus greening disease in Indonesia, we explored pathogens ofDiaphorina citri which vectors the disease. At two orange orchards, manyD. citri adults were found to be dead and covered with fungal mycelia. Two fungi,Paecilomyces fumosoroseus andHirsutella citriformis, were consistently isolated from the infected insects. Molecular phylogeny of their 18S rDNA sequences showed that they belong to the ascomycetous clade of the Clavicipitales/Hypocreales, which embraces many entomopathogenic fungi. When healthy adults ofD. citri were inoculated with conidia of theP. fumosoroseus, the insects died within 6 d.