''Cacopsylla pyri'', commonly known as the pear psylla, pear psyllid, or by its synonym ''Psylla pyri'', is an insect in the subfamily
Psyllinae
Psyllinae is a subfamily of plant-parasitic hemipterans in the family Psyllidae. It includes minor pest species such as: the apple psylla, '' Cacopsylla mali'' and '' Cacopsylla pyri'' (a.k.a. '' Psylla pyri''), commonly known as the pear psyll ...
. 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
Adult ''C. pyri'' are 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, which occurs between each moult (''ecdysis'') until sexual maturity is reached. Arthropods must shed the exoskeleton in order to ...
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 (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 no official boundary exists, the most common ...
.
Life cycle
This psyllid 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'' and '' Deraeocoris'' spp., the green lacewing '' Chrysoperla carnea'' and several ladybirds. The wasp ''Trechnites psyllae'' ( Encyrtinae) 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
''Cacopsylla pyri'' damages pear trees by sucking the plant sap
Sap is a fluid transported in the 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 sep ...
; 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 (: stomata, from Greek language, Greek ''στόμα'', "mouth"), also called a stomate (: stomates), is a pore found in the Epidermis (botany), epidermis of leaves, stems, and other organs, that controls the rate of gas exc ...
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, and its peptidoglycan, around their cell membrane. The absence of peptidoglycan makes them naturally resistant to antibiotics ...
in their saliva
Saliva (commonly referred as spit or drool) 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 ...
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
''Pyrus pyrifolia'' is a species of pear tree native to southern China and northern Indochina that has been introduced to Korea, Japan and other parts of the world. The tree's edible fruit is known by many names, including Asian pear, Persian pea ...
'' 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, China, and the Ussuri River area of far eastern Russia. It has flo ...
'' 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, from2=Q15704179, from1=Q2297547
Psyllidae
Hemiptera of Asia
Hemiptera of Europe
Hemiptera of North America
Insect vectors of plant pathogens
Taxa named by Carl Linnaeus
Insects described in 1758