Psylla pyri
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''Psylla pyri'', commonly known as the pear psylla or pear psyllid, is an insect in the family
Psyllidae 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 ( ...
. 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.


Description

The adult ''Psylla pyri'' is between long. The colour is variable, ranging between orange-red and black, the thorax having whitish longitudinal stripes on its upper surface. The wings are transparent, with dark veins and sometimes a smoky appearance near the base. Later
instar An instar (, from the Latin '' īnstar'', "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (''ecdysis''), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or ass ...
nymphs are purplish-brown or reddish-brown, with white longitudinal stripes and black patches; the developing wing-pads each bear a single knobbed bristle. The younger nymphs are yellowish with red-purple eyes.


Distribution

The species is found in Europe, including Scandinavia, and in Asia. In Britain it used to be very rare, with only one record before 1969, but since then it has become much more common, especially in the southeast of the country. It was introduced accidentally into North America, being observed in Connecticut in 1832 and arriving in Washington State by 1939, soon becoming a serious pest of pears in the
Pacific Northwest The Pacific Northwest (sometimes Cascadia, or simply abbreviated as PNW) is a geographic region in western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Though ...
.


Life cycle

This psylla overwinters as an adult, concealing itself in a crack in the bark. In spring it leaves
diapause In animal dormancy, diapause is the delay in development in response to regular and recurring periods of adverse environmental conditions.Tauber, M.J., Tauber, C.A., Masaki, S. (1986) ''Seasonal Adaptations of Insects''. Oxford University Press It ...
, and the female starts laying eggs round the base of the swelling buds. Later in the summer, the eggs are laid beside the midribs of the leaves, on the petioles and on the flower buds. The nymphs moult five times, and both nymphs and adults insert their mouthparts deep into the phloem tissue to suck the sap, secreting the excess fluid as honeydew.


Ecology

Research in an untreated orchard in Turkey found 32 predator and three parasitoid species of insect associated with this psylla. The predators included the predatory bugs ''
Anthocoris nemoralis ''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 ...
'' and '' Deraeocoris'' spp., the green lacewing '' Chrysoperla carnea'' and several
ladybirds Coccinellidae () is a widespread family of small beetles ranging in size from . They are commonly known as ladybugs in North America and ladybirds in Great Britain. Some entomologists prefer the names ladybird beetles or lady beetles as they ...
. The wasp '' Trechnites psyllae'' was the main parasitoid. In a research study in the United States, a single developing nymph of the predatory bug ''
Deraeocoris brevis ''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. Description ''D. brevis'' is a hemimetabolous insect, undergoing incomple ...
'' took 25 days to mature during which time it consumed about 400 eggs and nymphs of the pear psylla. Another predator, the running crab spider ''
Philodromus cespitum ''Philodromus cespitum'' is a species of running crab spider in the family '' Philodromidae.'' It is found in North America, Europe, North Africa, and parts of the Middle East and Asia. ''P. cespitum'' is a foliage-dweller, and is the most abunda ...
,'' preys on this species in European fruit orchards.Michalko, Radek; Dvoryankina, Viktoriya (1 June 2019). "Intraspecific phenotypic variation in functional traits of a generalist predator in an agricultural landscape". ''Agriculture, Ecosystems & Environment''. 278: 35–42. doi:10.1016/j.agee.2019.03.018.


Damage

''Psylla pyri'' damages pear trees by sucking the
plant sap Sap is a fluid transported in xylem cells (vessel elements or tracheids) or phloem sieve tube elements of a plant. These cells transport water and nutrients throughout the plant. Sap is distinct from latex, resin, or cell sap; it is a sepa ...
; leaves are yellowed and distorted and flower buds and fruitlets are shed. The excess honeydew produced by the insects coats the leaves, covering up the
stoma In botany, a stoma (from Greek ''στόμα'', "mouth", plural "stomata"), also called a stomate (plural "stomates"), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange. The pore is bor ...
ta, and encourages the growth of
sooty mould Sooty mold (also spelled sooty mould) is a collective term for different Ascomycete fungi, which includes many genera, commonly ''Cladosporium'' and ''Alternaria''. It grows on plants and their fruit, but also environmental objects, like fences, ...
. The size of fruit is decreased and tree growth is diminished. Honeydew can cause discolouration of fruit, leading to its being downgraded. Heavy infestations can result in "psylla shock", caused by toxins in the saliva and resulting in defoliation or fruit drop, which may also affect the following year's crop. The psyllia can also carry
mycoplasma ''Mycoplasma'' is a genus of bacteria that, like the other members of the class ''Mollicutes'', lack a cell wall around their cell membranes. Peptidoglycan (murein) is absent. This characteristic makes them naturally resistant to antibiotics ...
in their
saliva Saliva (commonly referred to as spit) is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is around 99% water, plus electrolytes, mucus, white blood cells, epithelial cells (from which DNA can be ...
which can cause disease of the conducting cells in the tree's
phloem Phloem (, ) is the living biological tissue, tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as ''photosynthates'', in particular the sugar sucrose, to the rest of the plant. This tran ...
. Failure of nutrients to be translocated downwards can cause root starvation, with trees either declining slowly or suffering from sudden collapse. Trees grafted onto ''
Pyrus pyrifolia ''Pyrus pyrifolia'' is a species of pear tree native to East Asia. The tree's edible fruit is known by many names, including: Asian pear, Japanese pear, Chinese pear, Korean pear, Taiwanese pear, apple pear, zodiac pear, three-halves pear, pa ...
'' or ''
Pyrus ussuriensis ''Pyrus ussuriensis'', also known as the Ussurian pear, Harbin pear, and Manchurian pear, is a species of flowering plant in the family Rosaceae. It is native to Korea, Japan, and the Ussuri River area of far eastern Russia. It has flowers in ...
'' rootstocks are more susceptible to this disease than those on ''
Pyrus communis ''Pyrus communis'', the common pear, is a species of pear native plant, native to central and eastern Europe, and western Asia. It is one of the most important fruits of temperate regions, being the species from which most orchard pear cultivars ...
''.


References

{{Taxonbar, from=Q15704179 Psyllidae Hemiptera of Asia Hemiptera of Europe Hemiptera of North America Insect vectors of plant pathogens Taxa named by Carl Linnaeus