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 in the family Psyllidae. It is one of two confirmed vectors of citrus greening disease. [1] [2] 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. [1] 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. [3] [4] In the whole of the United States and its territories, areas where this psyllid are found are under quarantine restrictions. [5]
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. [1]
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. [1]
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. [1]
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. [6] [7] Polyketide synthesis by the Profftella symbiont is increased when the insect is carrying the Huanglongbing pathogen Liberibacter. [8]
Another insect of the same genus, Diaphorina cf. continua (open nomenclature term describing an unnamed species similar to Diaphorina continua ), shares bacteriome symbionts. [7]
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. [6] Wolbachia is able to help Liberibacter survive bacteriophages by inhibiting cell lysis. [9]
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. [10]
The predatory Brachygastra mellifica and parasitoid Tamarixia radiata wasps can both help control D. citri. [11] 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. [3] 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. [3] There is laboratory evidence indicating it can also transmit another serious citrus disease caused by the Tristeza virus. [12]
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. [13] 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. [14] [15] Both adults and nymphs of the psyllid can be controlled by the use of a wide range of insecticides. [16] 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. [17]
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. [18] Attempts to demonstrate attraction of the psyllid to volatile (air-borne) odors have failed to produce an effective attractant. [19] 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. [20] 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. [21] 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. [22]
Hemiptera is an order of insects, commonly called true bugs, comprising over 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, assassin bugs, bed bugs, and shield bugs. They range in size from 1 mm (0.04 in) to around 15 cm (6 in), and share a common arrangement of piercing-sucking mouthparts. The name "true bugs" is often limited to the suborder Heteroptera.
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.
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.
Citrus tristeza virus (CTV) is a viral species of the genus Closterovirus that causes the most economically damaging disease to its namesake plant genus, Citrus. The disease has led to the death of millions of Citrus trees all over the world and has rendered millions of others useless for production. Farmers in Brazil and other South American countries gave it the name "tristeza", meaning sadness in Portuguese and Spanish, referring to the devastation produced by the disease in the 1930s. The virus is transmitted most efficiently by the brown citrus aphid.
Murraya paniculata, commonly known as orange jasmine, orange jessamine, china box or mock orange, is a species of shrub or small tree in the family Rutaceae and is native to South Asia, Southeast Asia and Australia. It has smooth bark, pinnate leaves with up to seven egg-shaped to elliptical leaflets, fragrant white or cream-coloured flowers and oval, orange-red berries containing hairy seeds.
Brachygastra mellifica, commonly known as the Mexican honey wasp, is a neotropical social wasp. It can be found in North America. B. mellifica is one of few wasp species that produces honey. It is also considered a delicacy in some cultures in Mexico. This wasp species is of use to humans because it can be used to control pest species and to pollinate avocados.
Psylla pyri, commonly known as the pear psylla or pear psyllid, is an insect in the family Psyllidae. Originating in Europe and Asia, it has spread to North America. It is a pest of pear trees, sucking the sap, damaging the foliage, flowers and fruit and diminishing the crop.
Aphis gossypii is a tiny insect, an aphid ("greenfly") in the superfamily Aphidoidea in the order Hemiptera. It is a true bug and sucks sap from plants. It is a widely distributed pest of a variety of agricultural crops in the families Cucurbitaceae, Rutaceae and Malvaceae. Common names include cotton aphid, melon aphid and melon and cotton aphid.
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.
Planococcus citri, commonly known as the citrus mealybug, is a species of mealybugs native to Asia. It has been introduced to the rest of the world, including Europe, the Americas, and Oceania, as an agricultural pest. It is associated with citrus, but it attacks a wide range of crop plants, ornamental plants, and wild flora.
Tamarixia radiata, the Asian citrus cyllid parasitoid, is an hymenopteran wasp from the family Eulophidae which was discovered in the 1920s in the area of northwestern India (Punjab), now Pakistan. It is a parasitoid of the Asian citrus psyllid, an economically important pest of citrus crops around the world and a vector for Citrus greening disease.
Anthocoris nemoralis is a true bug in the family Anthocoridae. The species is native to Europe and is introduced in North America. It is a predator of aphids, spider mites and jumping plant lice, and is therefore used as a biological pest control agent.
Olla v-nigrum is a species in the family Coccinellidae, in the suborder Polyphaga. The species is known generally as the ashy gray lady beetle. The distribution range of Olla v-nigrum includes Central America, North America, and Oceania. It is usually gray or pale tan with small black spots on its elytra and thorax. However, a variation can resemble Chilocorus orbus. This form is black with two red spots on the wing covers and has white on the edge of the prothorax.
Psylla buxi, known generally as the boxwood psyllid or box sucker, is a species of plant-parasitic hemipteran in the family Psyllidae. It is native to Europe and introduced to North America.
Deraeocoris brevis is a species of predatory plant bug in the family Miridae. It is native to North America where it feeds on plant pests in apple and pear orchards.
Spanioneura fonscolombii, is a species of plant-parasitic psyllid in the family Psyllidae which feed on box. It was first described by Arnold Förster in 1848 and is found in Europe. It is also found in the United States of America where it was accidentally introduced.
Cacopsylla pyrisuga, or the large pear sucker, is a species of true bug in the family Psyllidae known as a pest of pear trees (Pyrus) in Central and North Europe.