Diaphorina citri | |
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Asian citrus psyllid, Diaphorina citri | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Class: | Insecta |
Order: | Hemiptera |
Suborder: | Sternorrhyncha |
Family: | Liviidae |
Genus: | Diaphorina |
Species: | D. citri |
Binomial name | |
Diaphorina citri Kuwayama, 1908 | |
Diaphorina citri, the Asian citrus psyllid, is a sap-sucking, hemipteran bug now in the taxonomic family Psyllidae [1] . It is one of two confirmed vectors of citrus greening disease. [2] [3] It has a wide distribution in southern Asia and has spread to other citrus growing regions.
The Asian citrus psyllid originated in Asia but it is now also found in parts of the Middle East, South and Central America, Mexico, and the Caribbean. In the United States, the psyllid was first detected in Florida in 1998 and is now also found in Louisiana, Georgia, Arizona, South Carolina, Texas, and since 2003 in California. [2] In Southern California, the San Joaquin Valley, and Central Coast counties, such as San Luis Obispo, an eradication program has been instituted in an attempt to prevent it from becoming established. [4] [5] In the whole of the United States and its territories, areas where this psyllid are found are under quarantine restrictions. [6]
The adult psyllid is about four millimetres long with a fawn and brown mottled body and a light brown head. It is covered with a whitish, waxy secretion which makes it look dusty. The forewings are broadest at the back and have a dark edging around the periphery with a pale gap near the apex. The antennae are pale brown with black tips. These features distinguish it from the superficially similar African citrus psyllid. It typically adopts a head down, tail up posture as it sucks sap. Aphids are often also present on citrus and psyllids can be distinguished from them by being more active, jumping insects, whereas aphids are sedentary. In addition, the antennae of a psyllid has ten segments whereas those of aphids usually have four or six segments. Most aphids have cornicles on the abdomen and psyllids lack these. [2]
The psyllid nymph moults five times. It is a yellowish-orange color and has no abdominal spots. The wing pads are prominent, especially in the later instars. [2]
The eggs are approximately 0.3 millimeters long, almond-shaped, thicker at the base and tapering toward the top. They are at first a pale color but turn yellow and later orange before they hatch. The long axis is placed vertical to the surface of the leaf. [2]
The psyllid has a bacteriome organ specialized for carrying two of its bacterial symbionts. Candidatus Carsonella ruddii, which provides nutrition, lives inside uninuclear bacteriocytes around the organ. Ca.Profftella armatura, which provides nutrition, defense toxins, and carotenoids, lives inside the syncytial cytoplasm of the organ. [7] [8] Polyketide synthesis by the Profftella symbiont is increased when the insect is carrying the Huanglongbing pathogen Liberibacter. [9]
Another insect of the same genus, Diaphorina cf. continua (open nomenclature term describing an unnamed species similar to Diaphorina continua ), shares bacteriome symbionts. [8]
The insect can be infected by Wolbachia , which is then transmitted vertically via the egg. Wolbachia and Liberibacter can reside either within the U-shaped bacteriome, or mingle with gut cells as part of the gut microbiome. [7] Wolbachia is able to help Liberibacter survive bacteriophages by inhibiting cell lysis. [10] [11]
Eggs are laid on the tips of growing shoots, between and near the unfolding leaves. A female may lay up to 800 eggs during her lifetime which may be several months. The whole development cycle takes from two to seven weeks depending on the temperature and the time of year. [12]
The USDA-ARS, U.S. Horticultural Research Laboratory (USHRL), in Fort Pierce, FL, established the international Genome Consortium to complete the Asian Citrus Psyllid Genome (D. citri) in 2008. The USDA, ARS researchers produced the first gene sequences starting in 2005 and produced the first draft transcriptomes in 2009-2011, [13] draft genomes 2013-2017, [14] [15] the improved Official Gene Set, OGSv2.0 and diaci_2.0 genome by 2019-2022 [16] (Saha et al. 2017a; 2019; ). The release of the Diaci_genome version 3.0 [17] occurred in 2023-2024 [ https://doi.org/10.1101/869685;]. The genome, transcriptome and Official Gene Set, have enabled the identification of thousands of genes and proteins. [18] [19] [20] [21] [22] [23] [24] All these resources have enabled the development of broad strategic approaches to manage psyllid populations, like RNAi biopesticides. These datasets of interactions and tissues also provided new insights into the interactions of the bacterial pathogen Candidatus Liberibacter asiaticus, CLas, with psyllids, and the citrus host plants.
The major breakthroughs on psyllid management that were developed include three types of antisense oligonucleotides (double-stranded RNA, single stranded antisense oligos (like FANA [25] [26] and Morpholio's) [27] [28] [29] that can target the Asian citrus psyllid, and the bacterial pathogen [30] , without harming other beneficial insects, like pollinators and predators. Using the genomic data researchers developed the first RNA interference, RNAi, biopesticide to reduce psyllids [31] [32]
The predatory Brachygastra mellifica and parasitoid Tamarixia radiata wasps can both help control D. citri. [33] Lady beetles are also important predators.
Psyllid nymphs are found on new shoots of citrus trees. As they feed, they produce a toxin that causes the plant tips to die back or become contorted, preventing the leaves from expanding normally. [4] However, direct damage from feeding by the psyllid is considered minor compared with the role the psyllid plays as the only known nonhuman vector of citrus greening disease.
Feeding can vector bacteria that causes one of the most devastating of citrus diseases, citrus greening disease. Affected trees bear small, asymmetrical fruit which are partially green and which are unsellable because of their poor size and quality. [4] There is laboratory evidence indicating it can also transmit another serious citrus disease caused by the Tristeza virus. [34]
The Asian citrus psyllid has a number of natural enemies including hoverflies, lacewings, several species of ladybird and a number of species of parasitic wasp. [35] One of these wasps, Tamarixia radiata , has proved very effective at controlling the pest and has been successfully released and become established in a number of citrus growing areas including Florida. [36] [37] Both adults and nymphs of the psyllid can be controlled by the use of a wide range of insecticides. [38] Citrus greening disease is best controlled through an integrated strategy involving the use of healthy planting material, the control of vectors, and the prompt removal of infected trees and branches. [39]
Recent efforts have focussed on understanding the various sensory cues that the psyllid uses to locate its host plant. Insight into the insect's behavior may lead to better methods for its control. One study demonstrated that perception of reflected ultraviolet wavelengths enhanced attraction to a yellow trap. [40] Attempts to demonstrate attraction of the psyllid to volatile (air-borne) odors have failed to produce an effective attractant. [41] It appears that this tiny insect is attracted by color (yellow and UV wavelengths) and decides to stay and feed on a particular plant only after alighting on a leaf and tasting it by probing with its mouthparts (stylets). Small molecules such as formic acid and acetic acid stimulate probing activity. [42] These may be used in new, innovative traps or other devices.
Recent effort has illustrated that the spatial distribution of eggs and nymphs is a result of the movement patterns of gravid females in response to the oviposition sites. The dispersion indices were used to confirm the aggregated or contagious distribution pattern of D. citri population on the flushes within the tree and could be expressed by the negative binomial distribution. Measurable tests showed that distributions of eggs and nymphs in naturally occurring psyllid populations were highly aggregated, following initially aggregated migrations of adults and a contagious dispersion of adults on the flushes within trees as population densities increased. [43] Increased population density in the field resulted in greater dispersion of population was the consequence of females' dispersal and their selection of oviposition sites. Because the exponential increase in dispersion can be predicted by means of the population density of immature stages, a sampling plan was developed from the relationship between the dispersion behaviour and population density rather than the relationship between economic damage and population density. [44]
Citrus is a genus of flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including crops such as oranges, mandarins, lemons, grapefruits, pomelos, and limes. The genus Citrus is native to South Asia, East Asia, Southeast Asia, Melanesia, and Australia. Various citrus species have been used and domesticated by indigenous cultures in these areas since ancient times. From there its cultivation spread into Micronesia and Polynesia by the Austronesian expansion ; and to the Middle East and the Mediterranean via the incense trade route, and onwards to Europe and the Americas.
Chambourcin is a variety of grapevine belonging to the Vitis genus in the flowering plant family Vitaceae. It is a French-American interspecific hybrid grape variety used for making wine. Its parentage is uncertain, but genetic studies show it likely includes several North American Vitis species in its background including: V. berlandieri Planch., V. labrusca L., V. lincecumii Buckley, V. riparia Michx., V. rupestris Scheele, and V. vinifera. The hybrid was produced by Joannes Seyve who often used Seibel hybrids produced in the 1860s. The grape has only been available since 1963; it has a good resistance to fungal disease, and is one of the parents of the new disease resistant variety, Regent, which is increasing in popularity among German grape growers.
Citrus production encompasses the production of citrus fruit, which are the highest-value fruit crop in terms of international trade. There are two main markets for citrus fruit:
Psyllidae, the jumping plant lice or psyllids, are a family of small plant-feeding insects that tend to be very host-specific, i.e. each plant-louse species only feeds on one plant species (monophagous) or feeds on a few closely related plants (oligophagous). Together with aphids, phylloxerans, scale insects and whiteflies, they form the group called Sternorrhyncha, which is considered to be the most "primitive" group within the true bugs (Hemiptera). They have traditionally been considered a single family, Psyllidae, but recent classifications divide the group into a total of seven families; the present restricted definition still includes more than 70 genera in the Psyllidae. Psyllid fossils have been found from the Early Permian before the flowering plants evolved. The explosive diversification of the flowering plants in the Cretaceous was paralleled by a massive diversification of associated insects, and many of the morphological and metabolic characters that the flowering plants exhibit may have evolved as defenses against herbivorous insects.
Cordyceps is a genus of ascomycete fungi that includes about 600 worldwide species. Diverse variants of cordyceps have had more than 1,500 years of use in Chinese medicine. Most Cordyceps species are endoparasitoids, parasitic mainly on insects and other arthropods ; a few are parasitic on other fungi.
Wolbachia is a genus of gram-negative bacteria that can either infect many species of arthropod as an intracellular parasite, or act as a mutualistic microbe in filarial nematodes. It is one of the most common parasitic microbes of arthropods, and is possibly the most common reproductive parasite in the biosphere. Its interactions with its hosts are often complex. Some host species cannot reproduce, or even survive, without Wolbachia colonisation. One study concluded that more than 16% of neotropical insect species carry bacteria of this genus, and as many as 25 to 70% of all insect species are estimated to be potential hosts.
Citrus greening disease or yellow dragon disease is a disease of citrus caused by a vector-transmitted pathogen. The causative agents are motile bacteria, Liberibacter spp. The disease is transmitted by the Asian citrus psyllid, Diaphorina citri, and the African citrus psyllid, Trioza erytreae, also known as the two-spotted citrus psyllid. It has no known cure. It has also been shown to be graft-transmissible.
Spiroplasma is a genus of Mollicutes, a group of small bacteria without cell walls. Spiroplasma shares the simple metabolism, parasitic lifestyle, fried-egg colony morphology and small genome of other Mollicutes, but has a distinctive helical morphology, unlike Mycoplasma. It has a spiral shape and moves in a corkscrew motion. Many Spiroplasma are found either in the gut or haemolymph of insects where they can act to manipulate host reproduction, or defend the host as endosymbionts. Spiroplasma are also disease-causing agents in the phloem of plants. Spiroplasmas are fastidious organisms, which require a rich culture medium. Typically they grow well at 30 °C, but not at 37 °C. A few species, notably Spiroplasma mirum, grow well at 37 °C, and cause cataracts and neurological damage in suckling mice. The best studied species of spiroplasmas are Spiroplasma poulsonii, a reproductive manipulator and defensive insect symbiont, Spiroplasma citri, the causative agent of citrus stubborn disease, and Spiroplasma kunkelii, the causative agent of corn stunt disease.
An orange, also called sweet orange to distinguish it from the bitter orange, is the fruit of a tree in the family Rutaceae. Botanically, this is the hybrid Citrus × sinensis, between the pomelo and the mandarin orange. The chloroplast genome, and therefore the maternal line, is that of pomelo. The sweet orange has had its full genome sequenced.
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Coccinella transversalis, commonly known as the transverse ladybird or transverse lady beetle, is a species of ladybird beetle found from India across southern and southeastern Asia to Malesia and Australia. It is not to be confused with Coccinella transversoguttata, a widespread species in Europe and North America also known as the transverse ladybird. The alternative vernacular of small transverse ladybird may be used for C. transversalis in instances where these two species are discussed together.
Trioza erytreae, the African citrus psyllid, is a sap-sucking insect, a hemipteran bug in the family Triozidae. It is an important pest of citrus, being one of only two known vectors of the serious citrus disease, huanglongbing or citrus greening disease. It is widely distributed in Africa. The other vector is the Asian citrus psyllid, Diaphorina citri.
Liberibacter is a genus of Gram-negative bacteria in the Rhizobiaceae family. Detection of the liberibacteria is based on PCR amplification of their 16S rRNA gene with specific primers. Members of the genus are plant pathogens mostly transmitted by psyllids. The genus was originally spelled Liberobacter.
Diaphorina is an Old World genus of sap-sucking hemipteran bugs in the family, Liviidae. It includes an important pest of citrus: the Asian citrus psyllid, D. citri.
Spiroplasma citri is a bacterium species and the causative agent of Citrus stubborn disease.
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Spiroplasma phage 1-R8A2B is a filamentous bacteriophage in the genus Vespertiliovirus of the family Plectroviridae, part of the group of single-stranded DNA viruses. The virus has many synonyms, such as SpV1-R8A2 B, Spiroplasma phage 1, and Spiroplasma virus 1, SpV1. SpV1-R8A2 B infects Spiroplasma citri. Its host itself is a prokaryotic pathogen for citrus plants, causing Citrus stubborn disease.
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