# Psyllid

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.
Several genera of psyllids, especially among the Australian fauna, secrete coverings called "lerps" over their bodies, presumably to conceal them from predators and parasites.

## Subfamilies and genera

A recent (2021) review identified 10 subfamilies (with one from Madagascar, yet to be described), including:

### Acizziinae White & Hodkinson, 1985

* Acizzia Heslop-Harrison, 1961

### Amorphicolinae Burckhardt, Ouvrard & Percy, 2021

* Amorphicola Heslop-Harrison, 1961

### Aphalaroidinae Vondráček, 1963

* Aphalaroida Crawford, 1914
* Baccharopelma Burckhardt et al., 2004
* Burckhardtia Straube & Meritzki
* Connectopelma Šulc, 1914 (replacement name for Delina Blanchard nec Robineau-Desvoidy)
* Ehrendorferiana Burckhardt, 2005
* Freysuila Aleman, 1887 (syn. Indana)
* Pachyparia Loginova, 1967
* Panisopelma Enderlein, 1910
* †Primascena Klimaszewski, 1998
* Prosopidopsylla Burckhardt, 1987
* Russelliana Tuthill, 1959 (syn. Arepuna)
* Sphinia Blanchard, 1852
* Yangus Fang, 1990 (syn. Pallipsylla)
* Zonopelma Burckhardt, 1987

### Ciriacreminae

Authority: Enderlein, 1910
* Auchmerina Enderlein, 1918
* Auchmeriniella Brown & Hodkinson, 1988
* Caradocia Laing, 1923
* Ciriacremum Enderlein, 1910
* Euceropsylla Boselli, 1929
* Geijerolyma Froggatt, 1903
* Heteropsylla Crawford, 1914
* Hollisiana Burckhardt, Ouvrard & Percy, 2021
* Insnesia Tuthill, 1964
* Isogonoceraia Tuthill, 1964
* Jataiba Burckhardt & Queiroz, 2020
* Kleiniella Aulmann, 1912 (syn. Desmiostigma, Syndesmophlebia)
* Manapa Brown & Hodkinson, 1988
* Mitrapsylla Crawford, 1914
* Queiroziella Burckhardt, 2021
* Palmapenna Hollis, 1976
* Telmapsylla Hodkinson, 1992
* Trigonon (bug) Crawford, 1920

### Diaphorininae

Authority: Vondráček, 1951
* Diaphorina Löw, 1880 (syn. Brachypsylla, Diaphora. Gonanoplicus, Pennavena, Eudiaphorina)
* Parapsylla Heslop-Harrison, 1961 (syn. Agmapsylla)

### Katacephalinae

Authority: Burckhardt, Ouvrard & Percy, 2021
* Katacephala Crawford, 1914 (syn. Jenseniella)
* Lautereropsis Burckhardt & Malenovský, 2003
* Notophorina Burckhardt, 1987
* Tuthillia Hodkinson, Brown & Burckhardt, 1986

### Macrocorsinae

Authority: Vondráček, 1963
* Apsyllopsis Burckhardt & Queiroz, 2020
* Brinckitia Heslop-Harrison, 1961
* Colophorina Capener, 1973 (syn. †Otroacizzia)
* Epiacizzia Li, 2002
* Euphaleropsis Li, 2004 (syn. Peregrinivena)
* Euphalerus Schwarz, 1904
* Euryconus Aulmann, 1912
* Macrocorsa Vondráček, 1963
* Paraphyllura Yang, 1984
* Pugionipsylla Li in Li et al., 2006
* Retroacizzia Heslop-Harrison, 1961
* Tridencopsylla Li, 2002
* Trisetipsylla Yang & Li, 1984

### Platycoryphinae

Authority: Burckhardt, Ouvrard & Percy, 2021
* Allophorina Hodkinson, 1991
* Limbopsylla Brown & Hodkinson, 1988
* Padaukia Hollis & Martin, 1993 (syn. Peltapaurocephala)
* Platycorypha Tuthill, 1945 (syn. Neopsyllia)

### Psyllinae

Authority: Latreille, 1807; selected genera:
* Cacopsylla Ossiannilsson, 1970 (syn. Edentatipsylla, Hepatopsylla, Osmopsylla, Thamnopsylla, Psyllia)
* Psylla Geoffroy, 1762 (syn. Baeopelma syn. nov., Chamaepsylla syn. nov., Psylla (Labyrinthopsylla) syn. nov., Asphagis Enderlein, 1921)
Note: the genus Pachypsylla is now placed in the family Carsidaridae.

## Coevolution

Insect-plant interactions have been important in defining models of coevolution and cospeciation, referring to whether plant speciation drives insect speciation and vice versa, though most herbivorous insects probably evolved long after the plants on which they feed.

## Status as pests

With taxonomic revisions at genus level and above, species including agricultural pests, that have been classed as "Psyllids" may now placed in other families including the Carsidaridae, Liviidae and Triozidae.
Citrus greening, also known as huanglongbing, associated with the presence of a bacterium Liberibacter asiaticum, is an example of a plant pathogen that has coevolved with its insect vector, the "Asian citrus psyllid", ACP, Diaphorina citri, such that the pathogen causes little or no harm to the insect, but causes a major disease which can reduce citrus quality, flavor, and production, as well as causing citrus trees to die. ACP was found in Florida in 1998, and has since spread across the southern US into Texas. This disease was found in Florida citrus groves in 2005. Management methods to reduce the spread of this disease and psyllid populations depend on an integrated pest management approach using insecticides, parasitoids, predators, and pathogens specific to ACP. Due to the spread of citrus greening worldwide and the growing importance of psyllid-spread diseases, an International Psyllid Genome Consortium was established. Insect genomics provides important information on the genetic basis of the pest's biology which may be altered to suppress psyllid populations in an environmentally friendly manner. The emerging psyllid genome continues to elucidate psyllid biology, expanding what is known about gene families, genetic variation, and gene expression in insects. Thus far, two new psyllid viruses have been discovered, and are being examined as potential biological control agents to reduce psyllid populations. Psyllid cell cultures have also been established by several researchers working with virus propagation, and as a system to propagate C. liberibacter for molecular studies on infection and replication. Studies on the microbiota have also identified four new species of bacteria. Thus far, 10 microbial organisms have been identified within these psyllids, among them the primary endosymbiont, whose genome has been sequenced and posted at the NCBI database, as well as a Wolbachia species.