The impact of invasive species on biodiversity, food security and economy is increasingly noticeable in various regions of the globe as a consequence of climate change. Yet, there is limited research on how climate change affects the distribution of the invasive Asian citrus psyllid Diaphorina citri Kuwayama (Hemiptera:Liviidae) in Ghana. Using maxnet package to fit the Maxent model in R software, we answered the following questions; (i) what are the main drivers for D. citri distribution, (ii) what are the D. citri-specific habitat requirements and (iii) how well do the risk maps fit with what we know to be correctly based on the available evidence?. We found that temperature seasonality (Bio04), mean temperature of warmest quarter (Bio10), precipitation of driest quarter (Bio17), moderate resolution imaging spectroradiometer land cover and precipitation seasonality (Bio15), were the most important drivers of D. citri distribution. The results follow the known distribution records of the pest with potential expansion of habitat suitability in the future. Because many invasive species, including D. citri, can adapt to the changing climates, our findings can serve as a guide for surveillance, tracking and prevention of D. citri spread in Ghana.

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is the key vector insect transmitting the Candidatus Liberibacter asiaticus (CLas) bacterium that causes the devastating citrus greening disease (Huanglongbing, HLB) worldwide. The D. citri salivary glands (SG) exhibit an important barrier against the transmission of HLB pathogen. However, knowledge on the molecular mechanism of SG defence against CLas infection is still limited. In the present study, we compared the SG transcriptomic response of CLas-free and CLas-infected D. citri using an illumine paired-end RNA sequencing. In total of 861 differentially expressed genes (DEGs) in the SG upon CLas infection, including 202 upregulated DEGs and 659 downregulated DEGs were identified. Functional annotation analysis showed that most of the DEGs were associated with cellular processes, metabolic processes, and the immune response. Gene ontology and Kyoto Encyclopaedia of Genes and Genomes enrichment analyses revealed that these DEGs were enriched in pathways involving carbohydrate metabolism, amino acid metabolism, the immune system, the digestive system, the lysosome, and endocytosis. A total of 16 DEGs were randomly selected to further validate the accuracy of RNA-Seq dataset by reverse-transcription quantitative polymerase chain reaction. This study provides substantial transcriptomic information regarding the SG of D. citri in response to CLas infection, which may shed light on the molecular interaction between D. citri and CLas, and provides new ideas for the prevention and control of citrus psyllid.

Diaphorina is a species-rich genus, native to the tropics and subtropics of the Old World, particularly of more arid regions. One of the species, Diaphorina citri, is the economically most important pest of citrus. Diaphorina species are morphologically similar which makes their identification difficult. In this study, the accuracy of DNA barcoding, using mitochondrial cytochrome c oxidase subunit 1 (COI), geometric morphometrics of the forewing and digital image processing methods were tested for identification of the three Diaphorina species: D. chobauti, D. citri and D. zygophylli. Moreover, the published COI sequences of D. citri, D. communis and D. lycii obtained from Genbank were used for cluster analyses. DNA barcodes for D. chobauti and D. zygophylli are deposited in Genbank for the first time. The results of the molecular and geometric morphometric analyses are congruent and place D. chobauti as the sister taxon of the other Diaphorina species. The geometric morphometric analysis shows that in D. zygophylli the fore margin is slightly curved proximally and sharply bent distally, while in D. chobauti and D. citri it is straight proximally and weakly bent distally. The results of digital image processing show that the distribution of the dark pattern differs consistently in the three studied species.

Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), is an invasive citrus pest in southern California, which secretes honeydew and has the potential to spread a lethal bacterial disease, huanglongbing, of citrus. In urban citrus, Argentine ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae), also an invasive pest, tends honeydew-producing hemipterans. We used field data to determine whether the mutualistic relationship between L. humile and six established species of honeydew producers may hinder or favor the establishment of D. citri and its biological control with Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae) in citrus via competition or mutualism for ants, respectively. In the field, L. humile and D. citri are engaged in a mutualistic relationship. Ants harvest solid honeydew secreted by psyllid nymphs and tended more than 55% of observed D. citri colonies. Linepithema humile displayed a preference hierarchy when tending honeydew producers infesting citrus. It responded equally or less intensively to D. citri than to other honeydew-producing species. Consequently, the mutualism between L. humile and D. citri was affected by the presence of other honeydew-producing species, and the percentage of D. citri colonies tended by L. humile. The number of ants per D. citri colony also decreased as the number of other honeydew producers increased. Diaphorina citri density was also affected by the presence of other honeydew producers. Both colony size and the number of D. citri nymphs counted per tree decreased as the number of other honeydew producers increased. Our results indicate that competition between honeydew producers for the mutualist ant L. humile may hinder the establishment of D. citri by possibly facilitating increased biological control.

The Asian citrus psyllid Diaphorina citri Kuwayama is a destructive insect pest in citriculture, because it is an efficient vector of the proteobacteria ‘Candidatus Liberibacter asiaticus’ (Las), ‘Ca. L. africanus’ (Laf) and ‘Ca. L. americanus’ (Lam). These bacteria cause the ‘huanglongbing’ disease or ‘greening’ or ‘yellow dragon’ disease. The disease kills the plant and reduces fruit production. This insect pest is susceptible to entomopathogenic fungi, and we report the use of different strains of Metarhizium anisopliae, Cordyceps bassiana and Isaria fumosorosea against the nymphs and adults of D. citri under field conditions. The fungi were applied four times using a concentration of 2 × 1013 conidia/ha with a time interval of 15 days between applications. The percentage of control of Cb 108, Ma 65, Ma 14 and Ifr 4 was 60, 50, 40 and 35% in nymphs, and 50, 50, 42 and 22% in adults, respectively. Metarhizium anisopliae, C. bassiana and I. fumosorosea applied on Persian lime groves are more effective in reducing higher density of nymphs than adults of D. citri.

The Asian citrus psyllid, Diaphorina citri Kuwayama, vectors Candidatus Liberibacter asiaticus (Las) and Candidatus Liberibacter americanus (Lam), the presumed causal agents of huanglongbing. D. citri generally rely on olfaction and vision for detection of host cues. Plant volatiles from Allium spp. (Alliaceae) are known to repel several arthropod species. We examined the effect of garlic chive (A. tuberosum Rottl.) and wild onion (A. canadense L.) volatiles on D. citri behaviour in a two-port divided T-olfactometer. Citrus leaf volatiles attracted significantly more D. citri adults than clean air. Volatiles from crushed garlic chive leaves, garlic chive essential oil, garlic chive plants, wild onion plants and crushed wild onion leaves all repelled D. citri adults when compared with clean air, with the first two being significantly more repellent than the others. However, when tested with citrus volatiles, only crushed garlic chive leaves and garlic chive essential oil were repellent, and crushed wild onions leaves were not.

Analysis of the headspace components of crushed garlic chive leaves and garlic chive essential oil by gas chromatography-mass spectrometry revealed that monosulfides, disulfides and trisulfides were the primary sulfur volatiles present. In general, trisulfides (dimethyl trisulfide) inhibited the response of D. citri to citrus volatiles more than disulfides (dimethyl disulfide, allyl methyl disulfide, allyl disulfide). Monosulfides did not affect the behaviour of D. citri adults. A blend of dimethyl trisulfide and dimethyl disulfide in 1:1 ratio showed an additive effect on inhibition of D. citri response to citrus volatiles. The plant volatiles from Allium spp. did not affect the behaviour of the D. citri ecto-parasitoid Tamarixia radiata (Waterston). Thus, Allium spp. or the tri- and di-sulphides could be integrated into management programmes for D. citri without affecting natural enemies.

Introduction. The effects of imidacloprid and fenobucarb insecticides on thedynamics of the psyllid Diaphorina citri and on the incidence ofCandidatus Liberibacter asiaticus (Ca. L. a.), theputative causal agent of Huanglongbing disease (HLB), were studied in a field experiment.Materials and methods. The experimental design consisted ofthree independent 0.5-ha Citrus orchards planted with disease-freeHLB-susceptible orange trees, located in a Citrus producing areaseriously affected by HLB. Imidacloprid was applied monthly to the trunks in one orchardat a rate of 0.15 g a.i.·tree–1; fenobucarb was sprayed fortnightly in a secondorchard at a rate of 250 g a.i.·ha–1. The 3rd orchard was managed as a controlwithout insecticide applications. The total number of adult D. citrispecimens and the percentages of trees harbouring psyllid eggs and 5th instar nymphs weremonitored at fortnightly intervals in each orchard. Ca. L. a. incidencewas assessed in each orchard by PCR at 5 months, 12 months and 24 months after planting.Results. Compared with the control, both the fenobucarb and imidaclopridtreatments reduced adult psyllid populations by over 90% and reduced the frequency oftrees harbouring eggs and 5th instar nymphs. Only imidacloprid treatments totallyprevented development of a new generation of adults from eggs. Two years after planting,the prevalence of Ca. L. a. was 0.939, 0.745 and 0.239 in the control andin the orchards treated with fenobucarb and imidacloprid, respectively. Discussionand conclusion. The results indicated that, although both the insecticides usedeffectively reduced D. citri populations by killing adults and nymphs andby affecting or preventing psyllid reproduction in orchards, neither of the twoinsecticide treatments totally prevented transmission of Ca. L.asiaticus. However, due to its long-lasting effect and systemic activity, the imidaclopridtreatment provided the best protection against infections, and delayed and slowed down thespread of the pathogen. Furthermore, it reduced the number of pesticide applicationsneeded and left the way open for biological integrated pest management programmes.

Introduction. The Asian citrus psyllid, Diaphorina citri Kuwayama, is particularly harmful tocitrus plantations as it is one of the two psyllid vectors of the citrus greening disease or Huanglongbing. Thisdisease, which limits the longevity of trees, is due to an intracellular bacterium which mainly affects the phloem.Past experience of biological control of D. citri in Reunion Island. In Reunion Island, this disease,detected in 1967, was the main obstacle to the development of the cultivation of citrus fruit. Control of the vectorD. citri, by introducing from India and multiplying on site the specific parasitoid Tamarixia radiata(Waterston), was carried out during 1978 when nearly 4600 adult parasitoids were released. The success of T.radiata combined with the distribution of healthy plant material was at the origin of the revival of the cultivation ofcitrus fruit in Reunion Island. Programme for a biological control of D. citri in Guadeloupe. In Guadeloupe,D. citri was reported in January 1998. No trace of insect parasitism was found and only one fungus, Hirsutella citriformis Speare, proved, under certain conditions, capable of regulating the populations of thispsyllid. Taking into account the experience in Reunion Island and that the greening disease has not shown up inGuadeloupe, the introduction of T. radiata from Reunion Island was made in January 1999. About 1000 T.radiata were released all over the Guadeloupe islands. At present, just a little more than 1 year after the lastreleases, the parasitoid is established and present in almost all the citrus orchards where psyllid populations havedecreased considerably. Quite favorable biological characteristics play a great part in explaining the excellenteffectiveness of T. radiata in biological control programmes against D. citri.