''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.

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 o ...

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, 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'' and ''

Deraeocoris ''Deraeocoris'' is a genus of plant bugs in the family Miridae. There are at least 210 described species in ''Deraeocoris''. See also * List of Deraeocoris species References Further reading * * * * * * External links Bioli ...

'' spp., the green lacewing '' Chrysoperla carnea'' and several ladybirds. 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'' 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,'' 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 separat ...

; 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 bo ...

ta, and encourages the growth of sooty mould. 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 antibiotic ...

in their saliva which can cause disease of the conducting cells in the tree's

phloem Phloem (, ) is the living 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 transport process is ...

. 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'' or '' Pyrus ussuriensis'' rootstocks are more susceptible to this disease than those on '' Pyrus communis''.

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