Pear psylla

Pear psylla, Cacopsylla pyri, is a sap-feeding jumping plant louse associated primarily with European pear, Pyrus communis. Nymphs and adults cluster on tender shoots, leaves, flower structures, and fruitlets, producing sticky honeydew that can support sooty mold. In the United States, it must be distinguished carefully from the much more commonly documented Cacopsylla pyricola; reliable identification may require an expert or molecular confirmation.

Pear psylla is a tiny jumping plant louse in the family Psyllidae. Adults are generally about 2–3 mm long, with transparent wings held rooflike over the body. Nymphs are flattened, soft-bodied, and often partly concealed by waxy secretions and honeydew.

Both nymphs and adults insert piercing-sucking mouthparts into pear tissues. Heavy infestations may reduce shoot vigor, distort young leaves, interfere with fruit development, and leave sticky deposits that become dark with sooty mold. The exact species matters because several pear-feeding Cacopsylla are superficially similar, including C. pyricola, the principal pear psylla reported from much of the United States.

• Sticky, shiny honeydew on young shoots, leaves, flower clusters, and fruit.
• Black sooty mold developing on honeydew-coated leaves or fruit surfaces.
• Yellowing, curling, distortion, or premature drying of young pear leaves.
• Reduced shoot growth, weakened terminals, and possible flower or fruitlet drop when feeding is severe.
• Flattened yellow, greenish, brown, or dark nymphs clustered along leaf midribs, petioles, tender stems, or the calyx end of fruit.
• Tiny yellowish eggs near buds, on petioles, or along leaf midribs.

These symptoms are not species-specific. Confirmation of C. pyri may require an experienced entomologist, genital examination, or molecular testing because C. pyricola and other pear-feeding psyllids can look and behave similarly.

Infestation begins when overwintered adults colonize pear trees and lay eggs around swelling buds and newly developing shoots. Nymphs feed on phloem and other succulent tissues, while adults disperse locally by short flights and wind-assisted movement. Long-distance spread is most likely through infested nursery stock, scionwood, or other living pear material.

Excessive nitrogen, vigorous water-sprout growth, dense canopies, and broad-spectrum insecticide use that removes natural enemies can increase pest abundance or prolong outbreaks. Honeydew contamination is a direct result of sap feeding, not a fungal disease by itself.

Pear psylla overwinters as an adult, usually in bark crevices, sheltered tree sites, or nearby protected vegetation. Adults become active during mild late-winter or early-spring weather and lay elongated yellowish eggs near buds and on tender tissues.

Nymphs pass through five instars. Early instars are small and pale; later instars become darker and develop visible wing pads. Nymphs feed in protected positions along midribs, petioles, shoots, and fruit calyxes, producing honeydew and wax. New adults emerge after nymphal development and may produce additional generations during the growing season. Generation number varies with climate, host growth, and local population biology.

Use an integrated approach based on confirmed identification, tree growth stage, pest density, and the value of the crop. Remove heavily infested water sprouts when practical, improve canopy access and airflow, and rinse small trees with a firm spray of water to dislodge exposed nymphs and wash away honeydew. Repeat monitoring after treatment because protected nymphs may survive.

For commercial or high-value trees, coordinate decisions with the local Cooperative Extension service and use regional pear IPM thresholds where available. Avoid routine broad-spectrum sprays that can flare psyllids by killing predators and may select for insecticide resistance. If pear decline is suspected—particularly with rapid wilting, leaf curl, rootstock-specific decline, or tree collapse—submit plant and insect samples for diagnostic testing rather than attributing all symptoms to feeding injury.

Conserve naturally occurring predators such as flower bugs, predatory plant bugs, lacewings, lady beetles, spiders, and earwigs by reducing unnecessary broad-spectrum insecticide use. In protected orchard systems, commercially available natural enemies may contribute to suppression, but performance depends on release timing, temperature, orchard structure, and compatibility with other treatments.

For small trees, a strong water spray can reduce exposed colonies. Horticultural oils or insecticidal soaps may suppress accessible stages when permitted for the crop and applied with thorough coverage, but they generally require precise timing and repeat monitoring. Test any product on a small area first, avoid applications during heat or drought stress, and protect pollinators and beneficial arthropods.

• Buy pear trees and scionwood from reputable, inspected sources; do not move suspect material between states or regions.
• Inspect dormant trees and early spring growth with a hand lens for adults, eggs, and young nymphs.
• Avoid excessive nitrogen and unnecessary irrigation that promote highly succulent water sprouts.
• Prune water sprouts and overly dense growth during appropriate dormant or summer pruning windows, while avoiding excessive pruning that stimulates regrowth.
• Maintain flowering groundcover and diverse non-crop vegetation where practical to support predatory bugs, lacewings, lady beetles, and spiders.
• Use a beat sheet or white-card tapping method to monitor adults and nymphs rather than treating solely on calendar dates.
• Have questionable specimens identified before making a species-specific regulatory or control decision, especially because C. pyricola is more commonly encountered in the United States.

• Cacopsylla pyri is also known by the common name European pear sucker.
• It is frequently confused with Cacopsylla pyricola, which is the pear psylla most commonly documented in U.S. production areas.
• Honeydew from feeding nymphs can support sooty mold, making fruit and foliage look black even when the primary injury is insect feeding.
• Pear-feeding psyllids can be associated with transmission of pear decline phytoplasma, but the presence of a psyllid does not by itself prove that the tree has pear decline.
• The recognized host relationship for C. pyri is strongly centered on the genus Pyrus, with Pyrus communis documented as a major host.